technologies affecting water-use efficiency of plants and

TechnologiesAffecting Water-Use Efficiency of

Plants and Animals

Page

The Water Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243Plant Water-Use Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244Animal Water Use . . . . . . . . . .......0, . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245

The Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . + . . . . . . . . . . . . . 246Methods of Improving Plants and Animals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246Innovative Applications of the Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ..9...-.. 267

Chapter IX References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ...9 .. s....... . . . 267

Appendix 9-l.–Scientific Names of Potential ’’New’’ Agricultural Plants . . . . . . . . 269

List of Tables

Table No. Page57. Comparison of the Total Amount of Biomass Produced per Total Amount

of Water Used in Transpiration for Crop Plants. . . . . 0 . . . . . . . . . . . . . . . . . . . . . 24458. Comparative Water Use of Animals . . . . . . . . . ....+.... . . . . . . . 4 . . . . . . . . . . . 24659. Percent of the United States With Soils

Subject to Environmental Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25360. Proportion of Crop Dry Matter Produced That is a Harvestable Product. . . . . . 25361. Information on Potential New Crops for Arid and Semiarid Lands . . . . . . . . . . 25862. Results of ’’New” Crop Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25963. The Protein Content and Quality of Various Grains. . . . . . . . . . . . . . . . . . . . . . . . 26164. Starch and Moisture Content of Several Sources of Starch. . . . . . . . . . . . . . . . . . 26265. Buffalo Sales in 1981 .1...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26366. A Comparison of Cattle, Sheep and Rabbit Production

on Western Rangelands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....6.... 26467. Salt Tolerance of Crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26568. Halophytes With Potential for Agricultural Use . . . . . . . . . . . . . . . . + . . . . . . . . . . 266

List of Figures

Figure No. Page57. Working With Protoplasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24758. The Technique of Recombinant DNA Technology . . . . . . . . . . . . . . . . . . . . . . . . . 24859. A Generalized Method for Developing Drought-Resistant

and Drought-Susceptible Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . ~ . . . . . . . . . . . . . 25260. The Complex Production, Marketing, and Consumption Scheme For

a New Crop Entering the Commercial Market. This Diagram Illustratesa Potential Strategy for Jojoba Producers and Processors . . . . . . . . . . . . . . . . . . . 260

61. Two Methods for Producing Salt-Tolerant Organisms . . . . . . . . . . . . . . . . . . . . . . 265

Chapter IX

Technologies Affecting Water-UseEfficiency of Plants and Animals

In the past, agricultural scientists and pro-ducers in the United States often chose agri-cultural technologies for their contribution tohigh productivity. Essentially, these practicesmade the natural environment less hostile forplants and animals, a change from dependingon native organisms that were closely adaptedto sometimes harsh conditions. Today, as nat-ural resources become more limited and eco-nomic costs increase, biological technologiesthat use existing natural resources more effi-ciently are needed. In the arid and semiaridareas of the West, these practices would bewater-sparing and would use the special fea-tures of the region.

This chapter focuses on technologies that“stretch” the amount of plant or animal pro-duced per unit of water used. As such, thesetechnologies are well-suited to the arid/semi-

arid region. The emphasis here is on workingwithin the natural limits of arid and semiaridlands with sophisticated technologies to pro-vide an array of opportunities for sustainableagriculture.

Regardless of the quantity of water availablefor irrigation agriculture, it is likely that thesetechnologies will figure more prominently inthe region’s future. If the amount of wateravailable for Western irrigation is maintained,these technologies can add diversity to agricul-tural production in the region. If, however, ex-pectations of less irrigation water are realized,these technologies may be vital in easing thetransition to more suitable production systems.In dryland and rangeland agriculture, whereproduction is usually limited by water, thesepractices can help sustain some current stylesof production.

Water—the principal ingredient in living tis-sue—plays a vital role in biochemical reactions,maintains cell rigidity, moves materials withinplants and animals, and helps to heat and coolthem. Water continuously flows through mostorganisms and a certain quantity is an absolutenecessity. When plants open pores (stomata)in their leaves to take in carbon dioxide forphotosynthesis, water is lost by transpiration,a process significant because it is both essen-tial and considerable. Desert plants may con-sume 100 times their weight in water each dayeven though they physiologically require onlyabout 10 percent of that amount. While someplants are able to slow transpiration, it cannotbe stopped completely without also stoppingall plant growth.

Because of the large amounts of water theyuse, plants are a major component of the hy-drologic cycle, and technologies have beendeveloped to make hydrologic changes by mod-ifying vegetation (see chs. VI, VII, and XI).Because animals use much smaller amounts ofwater they are not usual l}’ considered to be partof the hydrologic cycle. Both animals andplants, however, are vital to agriculture, In aridand semiarid lands, where water often deter-mines survival and production, the efficiencywith which organisms use water has importantimplications for sustaining all types of agricul-ture.

plants have evolved a number of differentways of coping with water shortages. They may

243

244 ● Water Related Technologies for Sustainable Agriculture in U.S. Arid and Semiarid Lands

almost totally escape drought by germinating,growing, and reproducing before water be-comes limited or only after a heavy rainfall.They may “resist” drought with special ana-tomical and physiological mechanisms to takeup, store, and retain water. Or they may “tol-erate” drought with mechanisms to limit thedestructiveness of internal water deficits.

The relationship between plant growth andwater stress is complex. A number of differentdrought-resisting mechanisms may come intoplay during a plant’s life, and its sensitivity towater stress may vary with each. The differentmechanisms may involve disadvantages as wellas advantages. For example, a crop variety witha short growing season may mature beforedrought occurs, but in rainy years its yields arelikely to be less than that of a long-season varie-ty. This complexity has slowed the develop-ment of drought-resistant agricultural plants.

Animals exhibit a similar range of adapta-tions to limited water supplies. Some, such askangaroo rats, may never drink water, obtain-ing moisture instead from their diet or evenfrom dew, and excreting little water.

In order to be meaningful, comparisons ofthese and other differences in water use mustinclude both the amount of crop, forage, oranimal produced and the amount of waterused. The concept of water-use efficiency(WUE) allows this comparison. As a generalmeasure of efficiency, this term applies equallywell to plants and animals, but it is seldom ap-plied to animals because their relative wateruse is small.

Plant Water-Use Efficiency

For plants, biological WUE is defined as thetotal dry weight of plant material produced pertotal water lost by transpiration. Agronomistsoften use a different definition of WUE knownas “agronomic WUE, ” which is the amount ofharvestable or economic biomass produced perwater lost by transpiration and evaporation.These two definitions allow distinctions to bemade between inherent biological processesand the processes and conditions that apply toplants grown as crops (19).

Instantaneous measures of WUE are notmeaningful, since plants constantly adjustwater use to changing environmental condi-tions, Over the entire season, however, biologi-cal WUE is relatively constant for a givenspecies. Variations are common among species(table 57); these differences relate to time ofyear that plants grow, evolutionary history, andplant physiology. For example, grasses as agroup tend to use water more efficiently thanshrubs (27). But individual species of drought-adapted shrubs may use water more efficient-ly than some grass species.

Attempts to increase WUE by altering eitherphotosynthesis or transpiration have usuallyfailed, For instance, antitranspirants, chem-icals that reduce transpiration, have been in-vestigated extensively but have not been widelyused (14). While they can decrease transpira-tion effectively, they do not increase WUEbecause they also reduce photosynthesis andthus plant growth. There may be site-specificcircumstances in which this is not a disadvan-tage, such as in the control of plants alongstreams.

Table 57.—Comparison of the Total Amount ofBiomass Produced per Total Amount of Water Used

in Transpiration for Crop Plants

Biological water-use efficiency has been divided by potentialevapotranspiration in order to correct for climatic differences.

Biological water-use eff ic iencywith climatic correction Photosynthetic

Crop (kg/ha/da) a type

Alfalfa . . . 63, 90 C3

Oats . 90 C 3

Soybean . 102 C3

Potato . . . 106 C 3

Barley . . 106 C 3

Wheat . 112 C3

Corn . . . . 151,213 C4

Sorghum 200,240 C4

Millet. . . . 198,260 C4—aKllograms/hectare/day

SOURCE Wayne R Jordan, Ronald J Newton, and D W Rains, “Biological WaterUse Efficiency in Dryiand Agriculture,” OTA commissioned Paper,1982), table 1A, Original sources” L. J Briggs and H. L Shantz, “TheWater Requirement of Plants II A Review of the Literature, ” U S.Department of Agriculture, Bureau of Plant Industry Bulletin 285, 1913,C B Tanner, and T. R Sinclair, “Efficient Water Use in Crop Produc-tion, H M Taylor, W R. Jordan, and T R Sinclair (eds ) (Madison, Wis.’American Society of Agronomy, 1983), H L. Shantz and L. N. Piemeisel,“The Water Requirement of Plants at Akron, Colorado,” Journal of Agri-cultural Research 34:1093-1190, 1927, R. J Hanks, “Yield and WaterUse Relationships An Overview, ” Limitations to Efficient Water Usein Crop Production, H M. Taylor, W R. Jordan, and T R Sinclair (eds. )(Madison, Wis. American Society of Agronomy, 1983)

.-

Ch. /X—Technologies Affecting Water-Use Efficiency of Plants and Animals 245—

water-use improvements in the past haveoften resulted from increases in agronomicWUE because of the flexibility plants show inallocating resources into different plant parts.For example, tepary beans respond to overirri-gation by producing leaves instead of seeds.While biological WUE remains unaffected,agronomic WUE is decreased. Since beans arethe desired product, a knowledge of agronomicWUE is more important to crop managementand breeding. Also, crops can be managed tominimize soil evaporation or to change cropmaturity to shift yields to before or afterdrought occurs. Both changes can increaseagronomic WUE.

Animal Water Use

Significant differences exist in the amountof water required by different livestock andwildlife species (table 58). Some animals re-quire large amounts of freshwater for drink-ing. Others require little drinking water, sincethey can reduce water requirements when it

is limited, conserve available water, or acquiremost of their needs from food. A list of animals,in order of increasing adaptation to droughtwould be water buffalo, European cattle, Afri-can (zebu) cattle, wool sheep, hair sheep, goats,and camels (28). Water use also will vary de-pending on the nature of the forage and weath-er conditions.

Because animals use comparatively little wa-ter, there has been little effort to use or breedanimals that use less water. Instead, effortshave concentrated on ways to increase the ef-ficiency with which animals convert plant bio-mass into their own. As long as water use re-mains unaffected, this process improvesanimal WUE,

Biological v. economic (agronomic) yield alsoapplies to herds and single animals. Mainte-nance costs, in terms of water and food, aresubstantial for many single animals. In somecases breeding populations are maintainedfrom year to year and their requirements mustbe counted in total water- and forage-use effi-

Box T.—Three Carbons, Four Carbons, and Cam: Plant Physiology and Water Use

Plant biological WUE falls into three broad categories corresponding to differences in photosyn-thesis: CAM, CA, and CS types. These processes, by which sunlight is converted into organic mat-ter, are different enough to affect many features. CAM, or crassulacean acid metabolism, plantsuse water most frugally. Stomata open at night when evaporative demand of the air is low but,if water is plentiful, many CAM plants also take up carbon dioxide during the day, and water useincreases dramatically. Maximum growth rates of CAM plants such as cacti are low because ofvery low photosynthetic rates. Pineapple, the only agricultural CAM plant, is more productive thanmost. A large number of food and forage plants use four-carbon, or C4, physiology and have inter-mediate biological WUE—e.g., corn, sorghum, grain amaranth, and many warm-season rangegrasses. They have high photosynthetic rates and accumulate dry matter quickly. Most of the cerealgrains, almost all woody trees, many vegetables, and cool-season range grasses belong to the thethree-carbon, or C3, group. This group has the lowest biological water-use efficiency and also isleast effective in retaining the carbon absorbed.

These fundamental physiological differences have not been exploited agronomically yet. FewCAM species are of economic value now, but they may have potential for specific, high-value prod-ucts. While four-carbon species are efficient water users, they also grow best during hot summersand therefore consume large amounts of water over the total season. These species are generallysensitive to low temperatures, so they cannot be planted earlier or later to reduce summertimewater demands. Attempts to breed hybrids with the best features of each type have so far failed.

SOURCES: James R. Ehleringer, “Photosynthesis and Photorespiration Biochemistry, Physiology and Ecological Implications, “ Hortscience 14(3] .217222. 1979;James R Gilley and Elias Fereres-Casteil, “ Efficient Use of Water on the Farm, ” OTA commissioned paper, 1982, Wayne R Jordan, Ronald J Newtonand D W. Rains, “Biological Water Use Efficiency in Dryland Agriculture, ” OTA commissioned paper, 1982


Table 58.—Comparative Water Use Of Animals

Low daily water turnovers reflect a high water-use efficiency. Thus, the animals listed first use the leastwater

Body weight Daily water turnoverAnimal (kg) (ml /kg082) Environment

Antelope:oryx . . . . . . . . . . . . . . . ~ ~ . . ~ . . ~ 136 70 African grasslandWildebeest. . . . . . . . . . . . . . . . . . . 175 137 African grasslandKongoni . . . . . . . . . . . . . . . . . . . . . 88 116 African grasslandEland . . . . . . . . . . . . . . . . . . . . . . . 247 213 African grassland

Goat:Somali . . . . . . . . . . . . . . . . . . . . . . 40 185 African desert

Camel:Somali . . . . . . . . . . . . . . . . . . . . . . 520 188 African desert

Sheep:Dorper . . . . . . . . . . . . . . . . . . . . . . 42 170 African grasslandMerino . . . . . . . . . . . . . . . . . . . . . . 38 180 African grasslandOgaden. . . . . . . . . . . . . . . . . . . . . 31 197 African desertKarakul . . . . . . . . . . . . . . . . . . . . . . 31 205 African grassland

Cattle:Boran . . . . . . . . . . . . . . . . . . . . . . . 417 224 African grasslandBoran . . . . . . . . . . . . . . . . . . . . . . . 197 347 African desert

SOURCE L. A Stoddart, A. D Smith, and T W Box, Range Management (New York: McGraw-Hill Book Co, 1975), p 318. (Originalsource Mac Farlane. “Prospects for New Animal Industries: Functions of Mammals in the And Zone, ” Proceedingsof the South Australian Water Research Foundation (Adelaide, S Australia, 1972).)

ciency of the herd. Of the animals slaughtered, selected for “agronomic” efficiency: faster andonly a portion is economic yield. About 50 per- greater weight gains in marketable productscent of an animal is used for meat, while by- per total nutrients spent for animal mainte-products of various kinds account for another nance.15 to 20 percent. Like plants, animals have been

THE TECHNOLOGIES

Methods of Improvingand AnimaIs

Biotechnologies

INTRODUCTIONThe term “biotechnology” has come to repre-

sent a cluster of methods for introducing andreproducing new genetic variation in bacteria,plants, and animals as well as a number of in-dustrial applications of biological processes. Inthis section, only those technologies are con-sidered that may increase the WUE of agricul-tural plants. The application of similar tech-nologies to animals is discussed under “AnimalBreeding. ”

The promising technologies include tissueculture and other techniques for propagatingorganisms; fusion of plant cells (protoplasts)

either within or betweenrecombination of DNA,

species; and precisethe genetic material

(figs. 57 and 58). These methods usually involveintensive laboratory treatment and may be usedalone, in conjunction with one another, or withmore conventional breeding methods.

ASSESSMENT

The application of various kinds of biotech-nology to the specific problems of water usein arid and semiarid lands involves manipula-tion of the mechanisms that influence the up-take, use, and loss of water by organisms, Forexample, some experts speculate that thedrought tolerance present in some westernweeds could be added to unrelated crops. O rperhaps cell lines selected for salt tolerancecould produce crops for irrigated areas withsalt accumulation.

Ch. IX–Technologies Affecting Water-Use Efficiency of P/ants and Animals . 247—

Figure 57.— Working With Protoplasts

“Clones” of a parent plant can be regenerated from itsisolated protoplasts by the methods developed for culturingtissues as shown here. Protoplasm fusion Involves an addi-tional step: protoplasts of two genetically unlike parentswould be combined at step 4. The offspring are not like eitherparent, they often contain unique combinations of geneticmaterial that could not be produced with conventional plant-breeding methods.

9

Small terminal leaves are first removed from a youngpotato plant (1). The leaves are placed in a solution contain-ing a combination of enzymes capable of dissolving the cellwalI (2). Another substance in the solution causes the pro-toplasts to withdraw from the cell wall and to becomespherical, thereby protecting the Iiving protoplasm during thedisintegration of the wall (3). The isolated protoplants are nexttransferred to a culture medium (4), where they grow, synthe-size new cell walls and begin to divide (5). After about 2 weeksof culture each protoplant has given rise to a clump of modi-fier-estimated cells, called a microcallus (6). The microcallusesare transferred to a second culture medium, where theydevelop into full-size calluses (7). At this stage the cells of thecallus begin to differentiate, forming a primordial shoot (8).The shoot develops into a small plant with roots in a thirdculture medium and is then planted in soil (9).

SOURCE James F Shepard The Regeneration of Potato Plants From Leaf.Cell Protoplasts, Scientific American 246156 May 1982

Some of these technologies are rapidly enter-ing agriculture. Tissue culture is already incommercial use and, in the next 10 to 15 years,is likely to make important contributions (23).Other biotechnologies face a potentially longperiod of basic research before their applica-

tions will be available. Protoplasm fusion, likeother more complex techniques, cannot beused now with much expectation that thedesired results will occur. Recombinant DNAtechnology holds the most promise for precise-ly changing plant features, but it is farthestaway from wide-scale development. Few prac-tical applications of these technologies are ex-pected within the next decade.

Institutional constraints exist in addition tothe technical ones. There is concern, for ex-ample, that reliance on laboratory practicesmight narrow the genetic diversity of presentcrops to an undesirable degree. On the otherhand, some believe that human-induced varia-tion and the germplasm banks that mightspring up could actually increase genetic diver-sity. Other concerns regarding the release ofnovel and potentially dangerous organisms intothe environment have diminished. For exam-ple, experience has shown that safeguardsare generally adequate to contain potentiallytroublesome organisms used in industry.

These technologies have already had an im-portant effect on the way agricultural researchis conducted. Some private universities andcorporations are involved in agriculture for thefirst time. Few of these leading-research institu-tions are also involved directly in arid landstudies. Furthermore, rapid industrial expan-sion has created at least a short-term shortageof trained personnel. As scientists and techni-cians move rapidly into the private sector,universities are concerned that their ability toconduct basic research and to train new teach-ers will be jeopardized. It is not clear to whatextent the large involvement by profitmakingcorporations may shape research priorities. Ifpublic sector research—e.g., at land g ran tuniversities, USDA laboratories, and State agri-cultural experiment stations—does not keeppace, there may be little progress in the applica-tion of new biological technology to problemsof social importance that have little foreseeableprofit. Also, since new life forms can bepatented, there is concern that limited accessto the results of private research may furtherlimit public work,

248 ● Water Related Technologies for Sustainable Agriculture in U.S. Arid and Semiarid Lands——. . — — —

Figure 58.-The Technique of Recombinant DNA Technology

2 Tissues

1(3 Plasmld I13 Labora tory scale

fermentat ion/{A-

SOURCE: U.S. Congress, Office of Technology Assessment, The Impacts of Applied Genetics (Washington, D. C.: US Government Printing Office, OTA-HR-132, 1981),p. 6; and Genentech, Inc

No consensus exists on biotechnology’s near-term potential in agriculture. While muchformer skepticism has been allayed, these arecapital-intensive enterprises that are capturinglarge amounts of public research money at atime when funds are limited. Therefore, thefear exists that less glamorous technologies—e.g., new approaches to classical plant breeding—will be overlooked.

Tissue Culture

Tissue culture is basic to the use of the otherbiotechnologies discussed here and to makingthe results of such biotechnologies available toagricultural scientists. It is accomplished byseveral methods (fig 57). In its simplest form,individual sexual cells such as pollen grainsand eggs are stored and grown in artificialnutrient media, More complex methods allow

identical plants to be developed from pieces ofthe parent after they receive several hormonetreatments. In another type of culture, the ini-tial unspecialized tissue, or callus, developedfrom a plant cutting is agitated to separate thecells; a new plant then regenerates from eachcell. This more productive method can also beused to expose genetic variation among the in-dividual cells of a single parent plant. If en-vironmental stress is applied then to theculture, the survivors can be regenerated. Thismethod may have important applications forproblems of water stress.

Many important crop and forage plants canbe regenerated from cuttings with these tech-nologies. Strawberries, asparagus, pineapple,coffee, and horticultural plants are mass pro-duced this way. More recently, mass propaga-tion of alfalfa, jojoba, and some grass species

—

Ch. IX—Technologies Affecting Water-Use Efficiency of Plants and Animals 249— — — — —

Photo credits: USDA-Agricultural Research Service

Wheat plants growing using tissue culture: white clump (left) are cells forming from live wheat anthers, masses of undifferentiated tissue grow-from the cells (center test tube), in a special growing medium (right test tube ‘and flask in

right photo), a small plant develops from the cultured tissue.

has become possible. The savings in time andspace can be substantial. For example, 25gallons (about 100 liters) of Douglas fir cells innutrient media can produce enough plants in3 months to reforest about 120,000 acres ofland (12).

When tissue culture techniques are used inconjunction with classical breeding methods,new germplasm can be made available rapid-ly, and the volume of material accumulated bydifficult crosses can be increased quickly. Forexample, 65 new types of potatoes have been“cloned” from Russet Burbank cells and morethan 134 virus-tree potato cultures have beendeveloped.

A number of water-related stresses can be ap-plied to plant-cell cultures, including salinity,drought, flooding, ion toxicities, nutrient defi-

ciencies, and temperature extremes. Cell lineswith resistance can be developed from the sur-vivors. Recent experiments suggest that cellselection may provide researchers with mate-rial less susceptible to water stress (19). For ex-ample, alfalfa and rice cell lines have been ob-tained that tolerate 2 percent sodium chloride,a salt concentration lethal to nonselected cells,Gene dosage, or the number of duplicate setsof genetic material present within a giveno r g a n i s m , can also be altered by t r e a t i n g

cultured cells with chemicals. Varieties of ryediffering only in gene dosage varied in sus-ceptibility to cold and observations suggest thata similar relationship holds for susceptibilit y

to water stress.

These treatments of plant cultures are recent,so it is difficult to evaluate their eventual im-

25-160 0 - 17 : QL 3

250 ● Water Related Technologies for Sustainable Agriculture in U.S. Arid and Semiarid Lands— .

“pacts. Sodium chloride tolerance in cell lines,for example, is sometimes unstable and doesnot occur in later generations. In other cases,important water-related features characterizethe whole plant but not isolated cells andtissues. Selection for these traits cannot be ac-complished in cell culture.

Protoplasm Fusion

If single plant cells in cultures are treated fur-ther to remove the tough cell wall, protoplastsremain. Protoplasts can then be combined, acrude way of creating new mixtures of genet-ic material that normally are prevented bynatural breeding barriers (fig. 57). This methodhas been used with petunias, plants in the cab-bage family, and tomato/potato pairs (poma-toes). Protoplasts from more distantly relatedspecies, such as tobacco and soybean, also havebeen induced to fuse. So far, it is possible tocomplete the necessary steps—strip the plantcell wall, alter the protoplasm, regrow a cellwall, form a callus, and regenerate the plant—for only a few species. Until the fusion processis further refined, the features of the new plant

will be unpredictable combinations of theparents.

This technique holds promise for creatingunconventional hybrids before the more pre-cise recombinant DNA technology is available.Combinations such as “pomatoes” do not havecommercial value now, but investigators hopethat closer crosses may. Wild relatives of cropplants often possess desirable features thatadapt them to stress, but natural barriers existto sexual crosses. For example, disease-resist-ant wild relatives often cannot breed with com-mercial potatoes. Protoplasm fusion may be ableto add this desirable genetic material topotatoes without breeding (25). The same proc-ess, or recombinant DNA techniques, may beapplicable to the transfer of water-relatedcharacters such as changes in growth rate andproduction of “heat-shock” proteins (6).

Recombinant DNA

Recombinant DNA technology uses enzymesto break apart the genetic material (DNA mol-ecules) in one organism and recombine it with

Photo credits: USDA.Soil Conservation Service

The grama grasses are important native Western forage plants. Biotechnologies such as tissue culture and conventionalplant breeding are used for these types of plants as well as for the major annual crops

Ch. IX—Techno/ogies Affecting Water-Use Efficiency of Plants and Animals . 251—

DNA pieces from another (fig. 58). The “recom-bined” material expresses new predeterminedcharacteristics in the organism into which itis inserted. This process takes place in fourstages:

1.

2.

3.

4.

Desirable genes are chosen and “vectors”are identified to carry them to the host.The gene is prepared for splicing into thevector.The vector is inserted and maintained inthe host.A number of hosts are cloned and the mostdesirable is selected for further modifica-tion or conventional breeding.

This methodology is far from routine forplants. The lack of vector systems and prob-lems with regenerating whole plants havehindered progress. The genetic material ofmicro-organisms is simpler and transfers ofDNA among bacteria or yeast are common.Therefore, near-term agricultural applicationsare likely to involve only microbes, eitherdirectly or as models for higher plants. For ex-ample, bacterial osmoregulation has been ma-nipulated by moving the gene for proline pro-duction into nonproline-producing micro-organisms. The recipient bacterium increasedits rate of nitrogen fixation while waterstressed (21). Since osmoregulation is the proc-ess by which organisms control the uptake ofwater, it is crucial where water is limited.

Ultimately, all agriculture depends on car-bon compounds “fixed” by plants from at-mospheric carbon dioxide. Bacterial carbondioxide fixation systems are considered to bemodels for plant systems, and preliminarystudies suggest that bacterial systems can bealtered by genetic manipulation (3). Attemptsfocus on reducing photorespiration of C 3

plants, the process by which about 40 percentof the energy acquired by plants is lost beforeorganisms can use it.

Recombinant DNA techniques are oftenmore difficult to use with plants than withbacteria and yeasts. In plants, the geneticmaterial is confined within a nucleus, andthere are few vectors for passing geneticmaterial from the nucleus of one plant cell to

another, The first genes were inserted acrossnatural reproductive barriers between plantspecies in 1973, but the ability to transfer plantgenes at will is some time away.

Because of these constraints the thrust of re-combinant DNA work in plants is developing

laboratory techniques and understanding basicplant physiology. Much of the success of pastplant-breeding programs relied on the transferof large segments of genetic material. A clearknowledge of the DNA-level changes was notnecessary. Recombinant DNA work requiresthat the role of transferred genetic material beunderstood if it is to achieve its purpose andhave successful agricultural applications. Thisis not possible now.

Classical Plant Breeding

INTRODUCTION

Plant breeders have traditionally workedwith whole plants instead of the cells ormolecules that characterize biotechnology.Plant breeding generally involves six steps:

1.2.3.4.

5.

6.

choosing the crop for breeding,identifying the breeding goal,selecting methods to reach that goal,exchanging genetic material among orga-nisms,evaluating the resulting offspring underfield conditions, andproducing seed for distribution to pro-ducers.

Some technical parts of these steps havechanged little over time: hand-pollination tocross similar plants, data collection from ex-tensive field plots, and identification, by art aswell as science, of the most promising youn g

plants. New methods have changed other stepsa great deal. Centralized research and seed pro-duction centers, single-crop specialists, collec-tions of worldwide germplasm, and modernstatistical evaluation have changed the face ofcontemporary plant breeding. The availability

of genetic engineering technology promises tomake even more changes.

The philosophical basis for crop-plant breed-ing, which is fundamentally important in the

252 ● Water Related Technologies for Sustainable Agriculture in U.S. Arid and Semiarid Lands—— —

initial steps, may also be changing. For exam-ple, the ability to be productive under harshenvironmental conditions, such as those im-posed by drought, has not been a major breed-ing goal for most crop species. In fact, mostplant breeding has involved selecting plants forsuperior yield in fertile environments or underother conditions of high external inputs (7).This approach assumes that plants which havehigh yields under irrigation or high fertiliza-tion will also have high yields when water- ornutrient-stressed. General plant adaptability issought to a range of conditions. This is the mostcommon approach to crop breeding and, fordryland crops, it has increased yields withoutaffecting agronomic WUE (10). In some cases,this type of plant breeding has reduced genet-ic variability for those factors, such as nitrogenfixation, stress tolerance, and photosyntheticefficiency, that may be beneficial in arid andsemiarid environments.

Another approach to plant breeding seeks,in the case of water shortages, to enhancedrought resistance in a manner similar to thatused successfully for disease and insectresistance (fig. 59). Key features that conferresistance are identified and incorporated intoless adapted varieties. Plant selection andevaluation are carried out under the samewater-limited conditions that the crops are ex-pected to endure because:

Breeding lines that use water efficiently ina dry environment may not do as well as otherlines under more favorable water conditions,This is because tradeoffs exist regarding plantresponses in different environments. There-fore selecting plants for wide adaptability maybe selecting for mediocrity. As a result, themost promising route for plant improvementunder drought stress probably involves selec-tion under water-limiting conditions (17).

Breeding programs of this type are commonfor forage plants, but similar ones for annualcrops constitute only a fraction of the totalbreeding effort. Because these programs arenew, they have yet to demonstrate their superi-ority to the first, more traditional, approach.They have the potential, though, for makingmajor contributions to agricultural production

Figure 59.—A Generalized Method for DevelopingDrought-Resistant and Drought-Susceptible Plants

Repeat as above for secondcycle of recurrent selection

because of the large geographic areas devotedto production of forage plants and the majorareas of cultivated cropland that are suscepti-ble to environmental limitations (table 59),

ASSESSMENT

Plant breeding for annual crops in the UnitedStates has a long and productive history. Ex-perts estimate that crop improvements have ac-counted for gains of 1 to 3 percent in yieldsper acre each year for corn, wheat, soybeans,cotton, and sorghum (19). Yield increases have

—

Ch. IX—Techno/ogies Affecting Water-Use Efficiency of P/ants and Animals . 253—

Table 59.— Percent of the United States With SoilsSubject to Environmental Limitations

Environmental l imitat ion Area affected (o/o)

Drought ., . ~ . . . . . . . . . . 25.3Shallowness . . . . . . . . . . . 19.6Cold . . . . . . . . . . . . . . . . . 16.5Wet . . . . . . . . . . . . . . . . . 15.7Alkaline salts . . . . . . . . . . . . . 2.9Saline or no soil . . . . . 4,5Other, . . . . . . . . . . . . . . . . . . 3.4None . . . . . . . . . . . . . . . . . . 12.1

SOURCE J S. Boyer, Plant Productivity and Environment,” Science 218445,Oct 29 1982

come from gradually altering combinations oftraits.

These include modifications of the partition-ing of plant substances among organs and com-pounds, changes in seed retention characters,and alterations in the timing of flowering andof seed formation. For example, economicyield is usually a fraction of total plant dry mat-ter, including roots (table 60). The size of thefraction depends on the plant species, watersupply, and management. A significant portionof the yield increases obtained by plant breed-ing have been based on increasing this fraction,In wheat, the proportion of harvestable grainhas increased from 35 to 50 percent over thelast 20 years (4). Selection pressure in otherplants would result in similar increases up to

Table 60.— Proportion of Crop Dry Matter ProducedThat is a Harvestable Product

‘Plant breeding has successfully Increased the proportion of plant-produced dry matter that IS a harvestable product The figuresgiven below are for highly productive Irrigated varieties

Proport ion economicCrop Product product (in percent)

Cotton .. .-., . . . . . lint ‘- 8-12Sunflower . . . . . . . . seed 20-30Bean ... . . . . grain 25-35Tomato ., ... . . . . . . fruit 25-35Soybean . . . . . . . . . grain 30-40Sorghum ... . . ., . . grain 30-40Corn . . . . . . . grain 35-45Sugarbeet . . . . sugar 35-45Wheat ... ., . . . grain 35-45Rice ... ... . . . . . . . grain 40-50Pineapple ... . . . . . . . . fruit 50-60Potato . . . tuber 55-65Alfalfa ... . . . . . . . . hay 40-80— .-SOURCE Adapted from Wayne R Jordan Ronald J Newton, and D W Rains

“Biological Water Use Efficiency in Dryland Agriculture, ” OTA commis-sioned paper 1982 p A 7, table 3A

the limits established by the anatomy of thecrop. When these increases do not increaseevaporation or transpiration, they result inhigher agronomic WUE,

Until recently, little research has been con-ducted on range plants, but work in Utah, Mon-tana, and the SCS Plant Materials Centers onplants for mined land reclamation has vitalizedrange-plant breeding. Vigorous, palatable,quickly established hybrid grasses are nowavailable. Perennial range-plant breeding dif-fers from breeding annual crop plants in sev-eral ways: survival, as well as production, isimportant; only enough seeds are needed to en-sure genetic mixing and reseeding; and stor-age reserves for the next season’s growth can-not be shunted into production. These require-ments make breeding more complex,

Identification of the character or charactersto be modified is the single most critical stepin plant improvement; it dictates both breeding

and evaluation methodology. Once charactersare identified, breeders have been successfulbecause they make selections from vast num-bers of plants. One breeding program that usescomputer-assisted seeding and harvesting al-lows seven staff members to test 30,000 plotsof plants in four locations (29). Large selectionsmay be important, especially for breedingdrought resistance, since it probably involvesmany genes with small, difficult to measure,effects.

In many cases, the fundamental mechanismsof adaptation to water stress are not known,where critical features can be identified forbreeding, they are not based on one or a fewgenes, unlike the many disease- and insect-resistance traits used successfull y in pastbreeding programs. Instead, the complex phys-iological and biochemical features that enablea plant to tolerate water stress vary from spe-cies to species. The properties that enable oneplant to survive in an arid region—e.g,, a largeroot system—may make another susceptible tosevere dedication, or drying,

Under such conditions, accurate laboratorymeasurements of the actual physiological fea-ture that confers drought resistance may re-

254 ● Water Related Technologies for Sustainable Agriculture in U.S. Arid and Semiarid Lands—. —. — —

quire hours. Measurement technologies are tootime-consuming for the large numbers of plantsneeded for mass evaluations. Therefore, directplant breeding for the biological characters thatdetermine drought resistance awaits develop-ment of better laboratory technology. Thisproblem can be overcome by correlating thesephysiological features with ones more readilyobserved and measured. Such genetic markersare used to identify some genetic diseases inhumans and in animal breeding programs.

With adoption of the 1970 Plant Variety Pro-tection Act and its 1980 amendments, institu-tional constraints to the development of newplant varieties decreased. Private investmenthas increased, and several times as many cot-ton, wheat, corn, and soybean varieties are be-ing produced as before its passage. Other con-cerns remain, however. The trend for smallseed companies to be taken over by large onesconcentrates economic power in fewer hands.There is concern that this may increase seedprices or hinder development of varieties thathave fewer customers or require fewer of acompany’s other products—e.g., pesticides.Fears also exist that the new systems for pat-enting germplasm will decrease germplasmavailability at a time when it is needed (5).

Animal Breeding

INTRODUCTION

Animal production is a major feature ofWestern agriculture. Large acreages in theWest cannot be cultivated because of erosionhazards or other factors. For these lands, pro-duction of animal protein or other products byruminants (goats, cattle, sheep, wildlife) is abeneficial use of unique resources. Also, largenumbers of cattle are raised on Western feed-lots. In both cases, animal breeding can in-crease productivity.

The major focus of most animal-breedingprograms is increasing the amount of animalbiomass produced per unit of land area or peramount of plant material consumed. This canbe accomplished by increasing the number ofyoung animals produced each year or by in-creasing the rate at which each offspring gainsweight.

Some breeding programs are related specif-ically to conditions prevailing in arid andsemiarid lands. For example, several newbreeds have been established to achieve greaterheat tolerance for Western rangelands. Thesehave involved the introduction of African andAsian sheep and cattle germplasm into Euro-pean stock, the common rangeland breeds.Santa Gertrudis, Beefmaster and Africandercattle, and Dorper sheep resulted from thesecrosses.

Standard animal-breeding technologies havebeen used to accomplish these goals: introduc-tion of new breeds to create hybrids, inten-tional selection for high growth rates amongpure breeds, and development of compositepopulations. A variety of more intensive tech-nologies are also finding their way into thelivestock industry.

ASSESSMENT

The productivity of ruminant farm animalshas increased substantially during the past twodecades. For example, selection for growth andcarcass traits within beef cattle breeds haschanged some traits by 2 to 3 percent everygeneration. Additional increases in productivi-ty have been obtained by crossing several cat-tle breeds: calf weight was increased by 20 to25 percent in a three-breed rotational breedingprogram, These programs have used Europeanbreeds such as the Simmental, Gelbviech, andMaine Angou, which are larger and later ma-turing. Other programs use Texas Longhornsto decrease calving difficulty, increase diseaseresistance, increase fertility, and adapt theanimals to the harsh environmental conditionsthat often prevail on open rangelands.

More intensive technologies, first used by thedairy cattle industry, are being adopted forother animals. Artificial insemination hasmarkedly increased milk production, and over50 percent of dairy cattle are bred this way, Ar-tificial insemination is used for only 3 percentof beef cattle, but recent treatments to synchro-nize ovulation promise to decrease labor re-quirements and make it more acceptable (20).For those 3 percent, though, artificial insemina-tion has dramatically improved weight, quali-ty and disease resistance.

Ch. IX—Technologies Affecting Water-Use Efficiency of Plants and Animals ● 255

Photo credit: IUDA-Soil Conservation Service

Texas longhorns, after hundreds of years of years of fending for themselves on the arid and semiarid ranges of Mexico,became the foundation of the U.S cattle industry. They were almost replaced by European cattle breeds in the 20th

century but interest in these hardy animals is increasing now

These improvements are being enhanced byembryo transfer and storage, methods similarto those used for plant-tissue culture. In em-bryo transfer, genetically superior cows aretreated with hormones and, as a result, produce6 to 20 eggs instead of one. These eggs areremoved, fertilized with semen from a genet-ically desirable bull, and transferred to sur-rogate mother cows. All of the calves will berelated to the superior genetic parents but willalso acquire the disease-resistance of the sur-rogate mother.

Some additional embryo manipulations arepossible before transplantation. New geneticcombinations can be made by combining two

embryos, or one embryo can be divided to pro-duce identical twins. All of these processes arecomplex and expensive. They require labora-tory facilities, trained embryologists, and about$2,000 for each procedure. These techniqueshave developed in conjunction with embryostorage methods. It is now possible to freezeembryos, conserving important genetic re-sources on a worldwide basis. Frozen embryosare often used in embryo transfer, and newtechnologies promise to make both proceduresless expensive and more widely available. Forexample, Rio Vista Farms in Texas have per-fected a method of transferring frozen embryosin plastic straws filled with protective fluid.With these, thawing and implantation can be

256 Water Related Technologies for Sustainable Agriculture in U.S. Arid and Semiarid Lands—.

done by veterinarians or less specialized per- Innovative Applicationssonnel. the Technologies

Some of this technology is not equally avail-able to ranches of different sizes and incomes.Smaller farms and ranches cannot usuallymanage the complicated rotational breedingprograms that increase productivity. Sinceabout 70 percent of the beef cattle in the UnitedStates are in herds of fewer than 100 animals,a large number of animals may be excluded,Composite populations of animals developedfrom a wide germplasm base selected fromseveral breeds would make the advantages ofhybrid vigor available to small cattle operatorsperhaps for the first time.

The cattle industry is in transition now, andchanging economic conditions will affect theavailability of credit and the location of live-stock centers. Some people expect that theWest will decline as a center for cattle feedingbut retain its prominence in rangeland cow/calfoperations (Ii). A continuing need will existfor animal germplasm suited for arid and semi-arid rangelands, but declining markets for redmeat may have unexpected effects on livestockproducers.

“NeW Crops": Plants and Animals

The greatest service which can be renderedany country is to add a useful plant to itsculture . . . .

Thomas Jefferson, 1821

The domesticated plants and animals raisedby American farmers and ranchers frequent-ly change. Seventy years ago avocados werevirtually unknown, soybeans were grown onlyin a few States, research on grain sorghum hadbarely begun, and European cattle were rela-tive newcomers: Now each of these organismsis well established, filling demands for high-value or drought-adapted human and animalfood.

Concern remains that other agriculturalplants and animals are needed. These are:

present agricultural organisms need diver-sification with new genetic material to pre-vent attack by new diseases and pests;

Box U.—Sunflowers: A Successful New Crop

Sunflowers are native American plants that, under some conditions, possess environmentaland economic advantages over other crops in the northern Great Plains: they offer drought andflood resistance and tolerance for salinity and frost. Several North American Indian tribes usedsunflowers extensively but large-scale commercial development of sunflowers occurred first inEurope. In 1964 the U.S.S.R. released the first high-oil variety, stimulating U.S. interest. Then,in the late 1960’s, the sharp decline in Russian exports opened the European market to U.S. ex-porters. At the same time, several universities, USDA, and a commodity organization increasedthe agronomic and economic attractiveness of the crop. Since then, U.S. acreage has expanded65 times to about 4 million acres. In North Dakota, South Dakota, and Minnesota, the major pro-ducing States, sunflowers have maintained their economic edge over other small grains, stood upto adverse weather conditions, and provided growers with an alternative crop. In 1980, a future’smarket was established, and other countries became eligible for financial assistance for U.S.sunflower purchases. While acreage continues to fluctuate, the future of sunflowers appears bright.

SOURCES: Gary L. Laidig and J. W. Twigg, “Historical Crop Studies,” Feasibility of lntroducing New Crops: Production, Marketing, Consumption (PMC) Systems,E.G. Knox and A. A. Theison (eds.) (Emmaus, Pa.: Rodale Press 1981), pp. 174191; E.D. Putt, “History and Present World Status,” Sunflower Scienceand Technology, J. F. Carter (ed.) (Madison, Wis,: American Society of Agronomy, 1978), pp. 1-29.


● current domesticated plants and animalsare too demanding on the environment;

● conventional crops, forages, and livestockrequire unacceptably high energy inputsin the form of fuel, nutrients, pesticides,irrigation, or disease prevention; and

● the lack of diversified markets exposesfarmers and ranchers to large foreign anddomestic price instabilities.

Some of these concerns have been shown tobe valid. For example, large geographic areasplanted in hybrids with a common geneticbackground caused the rapid spread of cornblight in the 1970’s, resulting in a nearly na-t ionwide crop failure. Disease-resistantmaterial in a germplasm bank was used tobreed resistant plants for the next season,preventing the problem from continuing. Agreater diversity of agricultural plants andanimals serve as long-term investments and in-

surance for the future if they can alleviate suchproblems.

In the short term, different crops and forageplants and animals may be able to provide newprofitable products and to diversify agriculturalmarkets. Some plant products may provide un-usual and high-value chemicals for the phar-maceutical, chemical, or energy industries,creating benefits for farmers and the Nationwhere such crops replace subsidized excesscommodities or ones that exhaust importantresources.

Some experts feel that “new” crops areneeded especially for the arid and semiaridregions of the United States. Of the establishedcrop plants, only barley, wheat, sorghum, cer-tain beans, and cotton are adapted to dry con-ditions. Some of these have been bred for highproduction under heavy irrigation, decreasing

258 ● Water Related Technologies for Sustainable Agriculture in U.S. Arid and Semiarid Lands—— . — . . . — — — — —— . —

their adaptation to drought. Other establishedcrops, such as hybrid corn, were not original-ly arid-land plants and may have inherent lim-itations in genetic material.

Opportunities exist today for examining thepotential of new plants and animals becauseof the uncertainty facing agriculture in theWest, In some places irrigation is no longerpossible. Lands need improvement to reachhigher levels of productivity in other areas.Even in the large areas of the West that are toodry and prone to erosion for conventional til-lage and harvest, it maybe possible to increaseagricultural productivity without jeopardizingimportant national resources. To this end, well-adapted plants and animals are being exam-ined, often for production without irrigation,heavy fertilization or other large inputs.

ASSESSMENT

A study for the National Science Foundationidentified 54 potential crops. Either theseplants are adapted to environmental stress orprovide a product critical to the needs ofAmerican society. Seven specifically are suitedfor arid or semiarid climates (table 61). Otherauthors have suggested additional potentialcrops for arid or semiarid zones. For example,Johnston (18) estimates that good evidence formedical usefulness exists for about 300 plantspecies of the Southwestern United States.

The status of these plants varies widely,Some, such as amaranth, tepary beans, guar,and cowpea, have a long history of use in theAmericas. Therefore, they are new only to con-ventional agriculture. These plants are alreadydomesticated, and their cultivation is welldeveloped for certain types of agriculture. Asizable ethnic market exists for these products,and supply cannot meet demand. Now theseold crops are ready for new and wider uses.

Other arid/semiarid-land plants are now be-ing domesticated, Some are at early stages ofdevelopment (jojoba, guayule, saltbush), where-as others are undergoing basic preliminary re-search (kochia, buffalo gourd, milkweed, Eu-phorbia, most medicinal plants).

The potential contribution to national pro-ductivity is not known for many of these crops.Preliminary assessments of biomass produc-tion indicate that levels are about one-fourthto one-half that expected from irrigated crops(19,22), but productivity would be expected toincrease with plant breeding (table 62), High-production levels over wide areas may not bethe goal for all crops, however. Some, such asthe traditional varieties used by Papago desertfarmers, may be best cultivated on smallerscales to maintain sources of already-adaptedgermplasm.

Table 61 .—Information on Potential New Crops for Arid and Semiarid Lands

Potentialmagnitude and

significanceLife Part

Crop span used

Xerophytes:Buffalo gourd. . . Perennial Seed

Marketcompetition

Land usecompetition

Culturaloperations

NeededworkProduct Adaptation

Protein andedible oil

Latex

Soybean Dry Desert Mechanized Large AgronomicMachineryAgronomicGuayule . . . . . . . Perennial Stem,

rootJojoba . . . . . . Perennial Seed

Syntheticrubber

Sperm-whale oil

Otherbeans

Cowpea

Dry Cotton Mechanized Large

Industrialoil

Vegetable

Dry,infertile

Dry

Desert Hand labor Large AgronomicMachineryAgronomicMung bean . . . . . Annual Seed Sorghum Mechanized Medium

Pigeon pea . . . . . Perennial/ Seedannual

Pinyon pine ... Perennial Seed

Bean Dry,infertile

Dry

Peanuts Mechanized Small AgronomicDemandAgronomicMachineryAgronomicDemand

Nut Nuts Forest Hand labor Medium

Tepary bean ... Annual Seed Bean Otherbeans

Dry,infertile

Range Mechanized Small

SOURCE Soil and Land Use Technology, Inc., A A. Theisen, E G. Knox, and F. L. Mann (eds.), Feasibility of Introducing Food Crops Better Adapted to EnvironmentalStress” (Washington, D.C U S Government Printing Office NSF/RA/780289, 1978), vol. 1, p 53, table 8.

Ch. IX—Technologies Affecting Water-Use Efficiency of Plants and Animals 259— —

Table 62.— Results of “New” Crop Experiments

Production Water available inCrop (Ib/acre) growing region (in)

Amaranth (grain) . . . . . . . 1,790 Not known (India)Cowpeas (seeds) . . . . . . . 895 5-1oGuar (seeds) . . . . . . . . . . 625-805 16-35Mesquite . . . . . . . . . . . . . . 1,790 12-16

12,530 24Guayule . . . . . . . . . . . . . . . 1,790-3,580 IrrigatedKochia . . . . . . . . . . . . . . . . 9,845 16Russian thistle . . . . . . . . 5,370-9,845 Not knownSaltbush . . . . . . . . . . . . . . 7,160 Not known (UT)

5,370 Not known (TX)

Present crops . . . . . . . . . . 22,375 IrrigatedSOURCE Various sources cited in: Wayne R Jordan, Ronald J Newton, and D. W.

Rains, “Biological Water Use Efficiency in Dryland Agriculture,” OTAcommissioned paper, 1982 )

The development of “new” animals has re-ceived less attention than plants. Individualranchers are experimenting with previouslyunused animals such as elk. Generally, theseefforts are not well known and the people in-volved are isolated from one another and fromthe established animal science community.

These plants and animals face barriers ofseveral kinds if they are to be used widely.Domestication, when necessary, is a time-consuming process, but sophisticated technol-ogy should shorten it significantly. Tissueculture techniques and other biotechnologiesmay contribute to the rapid development anddissemination of new germplasm and orga-nisms. However, more formidable barriers—both technical and institutional—exist. A greatdeal of research remains to be done for manyof the species described here, and there is lit-tle evidence to suggest that major Federal orState initiatives will be forthcoming. Often, ex-tensive field testing has not been completed.

Once these crops produce acceptable yieldsunder field conditions, they must be attractiveto producers and must find markets. Therehave been previous attempts, both successfuland unsuccessful, to introduce new crops. Ex-perience shows that markets and the institu-tional infrastructure for adoption are crucialto success. For example, processing plants maybe required, commodity organizations maybenecessary, consumers may have to be educatedabout new products, and marketing channels

from farm to consumer may have to be devel-oped (fig, 60). Even then, the adoption of a newcrop is unlikely to be entirely predictable,

Once a market for a new product exists,germplasm will probably be available to all in-terested growers. At the early stages of in-troduction, however, new crop production maybe limited to large landowners with the capitaland interest for major new ventures. For plantswith industrial uses, this may require corpora-tions to develop processing facilities first, thento obtain raw plant materials from local farm-ers on a contract basis or to grow them on theirown land.

Generally, there are few legal barriers to theintroduction of new crops or animals. A ma-jor exception, however, relates to reclamationof arid and semiarid surface-mined lands. BothFederal and State laws restrict the kinds of non-native plant species that may be used formineland revegetation. Therefore, potentialnew crop or forage plants that are not U.S.natives often cannot be included in some of thelargest research programs and experimentalplantings. Similarly, State laws that regulateownership of wildlife and Federal regulationsthat control slaughtering and quarantine of im-ported organisms are cases where the adoptionof technology is restricted legally. While theselegal restrictions are small compared to thesocial and economic barriers faced by newproducts, they can be significant.

Generally, these drought-adapted agriculturalproducts have the potential for tailoring agri-culture more closely to prevailing environmen-tal conditions. Where resources—e.g,, soils orwater—are being used faster than they arereplenished, adapted organisms hold hope fora more sustainable type of agriculture, For ex-ample, desert milkweeds may be able to replacedryland crops in the western Great Plainswhere increasing energy costs are eliminatingirrigation (1). Or, where fragile lands have beenplowed for annual crops and severe erosionhas resulted, adapted perennial shrubs, grasses,and forbs may provide profitable productswithout land degradation. Such potentials areusually long term. Few of the crops discussed

. .

260 Water Related Technologies for Sustainable Agriculture in U.S. Arid and Semiarid Lands

Figure 60.—The Complex Production, Marketing, and Consumption Scheme For a New CropCommercial Market. This Diagram Illustrates a Potential Strategy for Jojoba Producers and

Entering theProcessors

+I

SOURCE: G. L Laidig, “Jojoba. Simmondsia chinensis,” Feasibility of Introducing New Crops: Production-Marketing-Consumption (PMC) Systems, E. G Knowand A A. Theison (eds.) (Columbia, Md.: Soil and Land - Use Technology, Inc., 1981), pp. 74-101. -

Ch. IX—Technologies Affecting Water-Use Efficiency of Plants and Animals ● 261.-

Box V.—Rules, Regulations, and “New” Agricultural Plants

Federal and State laws restrict the types of plants that maybe used for reclamation of surface-mined lands. These legal limitations have had unexpected results on rangeland research programs.

The primary intent of most laws was to ensure a self-sustaining and persistent plant groundcover to protect soils. For example, Wyoming law requires that mine operators:

. . . establish . . . permanent vegetative cover of the same diverse seasonal variety native to thearea or of a species that will support the approved post-mining land use. This cover shall be capableof stabilizing the soil.

Wyoming law did not seek to prevent the use of all nonnative plant species but only those that:1) were not self-renewing and required special management for persistence, or 2) gave a false im-pression of reclamation success and might encourage damaging early grazing. The unintendedresult of the law, however, was the limitation of introduced plants in many reclamation andrangeland programs.

Is this desirable? The question is still being debated. Some contend that the focus on usingand improving native forage plants is long overdue and that it might lead to new styles of agricul-ture more adapted to arid/semiarid regions. Others believe that plant specialists should haveworldwide germplasm at their disposal and that introduced plants may provide important newadditions to American agriculture. For the time being, constraints on the use of nonnative plantsprovide an uncommon example of legal limitations on plant research.

SOURCE: Wyoming Department of Environmental Quality. Land Quality Division Rules and Regulations ch. IV.3.D.(2), August 1962.

here, with the possible exception of grainamaranth, are on the verge of becoming ma-jor national commodities, but timely researchand development are likely to provide impor-tant payoffs with sustained support. The do-mesticated desert crops such as cowpea andtepary bean, since they are adapted for cultiva-tion now and have developed markets, deserveespecially close examination.

Plants for Food and Forage

Grain amaranth was a staple crop of CentralAmerican Indians before colonizers, in orderto eradicate native cultures, methodically de-stroyed the fields. The remaining amaranthgermplasm is highly variable, providing richmaterials with which to work. Amaranth couldprovide biomass energy, seed starch, or leafyvegetables, but its high-protein grain is mostpromising. Both leaves and seeds contain pro-teins rich in lysine and methionine, aminoacids that limit protein digestion in other grains(table 63). Amaranth is well suited to semiaridconditions but not to prolonged or excessivedrought; some plants are adapted to nutrient-

Table 63.—The Protein Content and Qualityof Various Grains

Protein Limiting Relative protein scoreGrain (%) amino acid(s) (100 points optimum)Amaranth . . 15 Leucine 67Barley . . . . . 9 Lysine 58Buckwheat . . 12 Leucine 83Corn . . . . . . . . 9 Lysine 35Oats . . . . . . . . 15 Lysine 62Rice . . . . . . . 7 Lysine 69Soybeans . . 34 Methionine, 89

cysteineWheat . . . . . . 14 Lysine 47SOURCE: J P. Senft, “Protein Quality of Amaranth Grain, ” Proceedings of the

Second Amaranth Conference (Emmaus, Pa Rodale Press, Inc 1980),p 45

deficient soils but others require substantial fer-tilization, An accelerated program of amaranthresearch and development is underway at theOrganic Gardening and Farming ResearchCenter in Emmaus, Pa. The National Academy

of Sciences and the National Science Founda-tion sponsor amaranth research and USDA isalso showing interest (30).

Cowpeas, grown for their dry seeds in semi-arid regions of the world, sometimes produceseeds in years when drought causes other crops


Photo credit: Rodale Press, Inc.

This grain amaranth plant was selectedfor its compact form

to fail. Cowpea vegetation makes excellent hay,and cowpea’s high-protein seeds can be usedas animal protein concentrates. Green cowpeasare used now in the U.S. commercial canningindustry.

Buffalo gourds are native undomesticatedplants with wide distribution in the WesternUnited States. Each plant produces an abun-dant crop of gourds with oil and protein-richseeds and plant roots contain high-qualitystarch (table 64). Its vines are a potential foragethat can be repeatedly harvested. It is alsoreported to contain medicinal compounds. Do-mestication programs began for buffalo gourdin 1973 at the University of Arizona.

Plants for Biomass Energy

Current energy prices do not encourage thedevelopment of biomass crops. Some expertsbelieve that fragile arid and semiarid lands

Table 64.-Starch and Moisture Content ofSeveral Sources of Starch

Moisture StarchName of starch Source ( 0 / 0 ) (%0)

Buffalogourd a root . . Cucurbita foetidissima 68-72 15-17

Potato . . . . . . . . Solarium tuberosum 75-78 19Tapioca . . . . . . . Manihot utilissima 60-75 12-33Arrowroot . . . . . Maranta arundinaceae 65-75 22-28 b

aOnly buffalo gourd is an arid-land plant.Industrial starch yield Is typically 15 percent owing to cell structure.

SOURCE: W. P. Bemis, J. W. Berry, and Charles W. Weber, “The Buffalo Gourd:A Potential Arid Land Crop,” New Agricultural Crops, G. A. Ritchie (cd.)(Boulder, Colo.: Westview Press, 1979), p. 85.

should not be used for biomass productionunder most circumstances. But conditions maychange, and with appropriate safeguards, thefollowing plants may have potential for produc-ing biomass and other products.

Mesquites are a diverse group of woodylegumes from North and South America. Whilethey are commonly considered pests by ranch-ers, they have a long history of use for wood,flour, and fuel by other cultures. Mesquitegrows in areas of low rainfall by tappingground water, thus creating a potential prob-lem in some areas. Annual yields are current-ly low and plants are usually sensitive to lowtemperatures. But mesquite is one of the fewnitrogen-fixing legumes that can tolerate salin-ities equivalent to seawater and its diversityprovides material from which to breed im-proved varieties.

Saltbush is a common Western drought-resistant shrub. Many species have proteinconcentrations equivalent to that of alfalfa soit is important for forage. It has also been im-portant in revegetating disturbed lands.

Kochia (tumbleweed) and Russian thistle areboth “weeds” with potential for biomass fuelas well as forage. Their reputation as weedsmay hamper acceptability but it can also be ex-ploited for high productivity.

In other cases, agricultural residues can beused for biomass energy, plant and animal res-idue have potential (15).


Plants for Industrial Products

Guar is a leafy annual legume that producesgum and forage. Guar gum is a strengtheningand stabilizing agent in paper, cosmetics, proc-essed foods, and industrial materials. Olderplants withstand drought, and plant seeds with-stand alkaline or saline conditions. In 1977,20,000 tons of guar were produced but demandexceeded supply. U.S. consumption is expectedto be 41,500 tons in 1983 (31).

Guayule is a wild shrub, native to Mexicoand Texas. It is adapted to regions with lowand erratic rainfall. Plant roots and shoots con-tain rubber comparable to that produced by theAsian Hevea rubber trees, rubber that cannotbe duplicated synthetically. Guayule appearsto be suitable for mechanized agriculture andrequires little fertilization. It is not very salttolerant, and guayule plantations are current-ly susceptible to insects and diseases. TheNative Latex Commercialization Act of 1978(Public Law 95-592) was designed to stimulateguayule production, and the commercial rub-ber industry is involved in guayule researchand development. Two other sources of arid/semiarid lands natural rubber are rabbitbrushand sunflowers.

Soaps for shampoos are extracted from vari-ous species of yucca, and wax obtained fromthe seeds of jojoba is used for a variety ofcosmetics. Neither plant has been cultivatedin the United States but relatives of the yuccaare grown in other parts of the world. Jojobagrows in Arizona, California, and Mexico oninfertile or saline soils where rainfall is scarce.Jojoba wax is a substitute for sperm whale oil,with a large number of potential commercialuses in the cosmetic, pharmaceutical, and ma-chinery industries. The first large-scale ir-rigated commercial jojoba plantations are ex-pected to come into production in the South-west in 1983. At that time the price for seedsshould decrease, and the high-volume, low-costlubricant market should open.

Many species of plants produce copiousamounts of hydrocarbons that can providechemicals or be cracked to liquid fuels. Theprincipal species under development are milk-

weeds, gopherweed, and rabbitbrushes. Milk-weeds could provide a variety of chemicalproducts such as inositol and pectin andperhaps stimulate development of a honey beeindustry. Gopherweed produces a milky latexthat can be harvested without destroying theplant. Candelilla produces a wax with a highmelting point, and is a product imported fromMexico. Candelilla wax sells for $4.19 perkilogram ($1.90/lb) and the market is good (9).

Animals for Arid and Semiarid Lands

The American bison, or buffalo, was once themost important large grazer of Western lands.Bison have recovered from near extinction,and several large public and private herds nowexist (table 65). Buffalo ranchers suggest thatthese animals are more adapted to grazing onsemiarid lands than are their domestic counter-parts, They claim that buffalo use low-produc-tivity resources frugally, produce high-qualitymeat, and generally exhibit greater hardinessthan do domestic livestock.

Rabbits also have potential as new agricul-tural animals. They have short gestationperiods, multiple births, and short parentingtime. None of these features is shared with ma-jor domesticated animals of rangelands, andsuch characteristics provide the fastest way toincrease animal productivity per unit of plantproductivity (table 66). Rabbit farming is nowpracticed on a small scale, but the potential foropen-range ranching is unknown. Control, con-tainment, and slaughtering methods have not

Table 65.—Buffalo Sales in 1981

Number of AverageSale animals a

priceDakota Heritage Buffalo Sale,

Mitchell, S. Dak.. . . . . . . . . . . . . . . . 131 $572Wichita Mountains Wildlife Refuge,

Cache, Okla. . . . . . . . . . . . . . . . . . . . 123 $487Kansas Fish and Game

Commission, Canton, Kans. . . . . . 56 $582Custer State Park

Hermosa, S. Dak. . . . . . . . . . . . . . . . 470 $444Durham Ranch . . . . . . . . . . . . . . . . . . . 700 baThese figures include only one of the many private herds

Average price not available, individual price range $450 to $1,000

SOURCE. National Buffalo Association, “1981 Sales Results,” Buffalo 10(1), 1982,pp 8-9

264 . Water Related Technologies for Sustainable Agriculture in U.S. Arid and Semiarid Lands— . —

Table 66.—A Comparison of Cattle, Sheep andRabbit Production on Western Rangelands

Feature Rabbits Sheep CattIe

Offspring/100 females . . 1,485 120 90Weight per offspring (kg). . 1 39 182Population replaced

annually (0/0). . . . . . . . . . . 30 20 10Offspring harvested

annually/100 females . . . 1,455 100 80Harvested weight/

female (kg) . . . . . . . . . . . . 13 39 145Energy use per individual

(kcal) . . . . . . . . . . . . . . . . . 200,000 1,600,000 9,000,000Energy use per kg of

offspring (kcal) . . . . . . . . 19,000 40,000 62,000SOURCE Adapted from C W Cook, “Use of Rangeland for Future Meat Produc-

tion, ” Journal of Animal Science 451480, 1977, table 4

been developed, and large populations of un-controlled rabbits have sometimes become ma-jor pests. Limited markets are a major con-straint to developing a Western rabbit industry.

Limited experiments are underway on re-placing single-species domestic livestock withmixtures of species. The highest potential forthese approaches appears to be on rangelandswhere multiple use is important (ch. XI).

SaIt-Tolerant Organisms

INTRODUCTION

Salts occur in agricultural soils for a numberof reasons. Some soils and ground water sup-plies are naturally saline, and both soils andwater can gain salt from agricultural practicessuch as fertilization and irrigation. These proc-esses are heightened in arid and semiaridlands. High rates of evaporation and transpira-tion return pure water to the atmosphere, leav-ing salts behind. The chemical characteristicsof the salts vary. Chloride salts of sodium (tablesalt), calcium, and magnesium are all common,but sulfates and carbonates sometimes may re-place the chloride ions. Large areas of nonirri-gated croplands and rangelands in the north-ern Great Plains are experiencing salinity prob-lems, but irrigated areas, especially in Califor-nia and Arizona, are most affected.

Usually plant growth suffers once soils orwater are salinized. Salty water is difficult forplants to extract from soils, and such soils oftencontain high levels of potentially toxic ions (24).

Most common agricultural plants cannot tol-erate salinities of 10 to 20 percent seawater.Many are sensitive to even lower concentra-tions (table 67).

The productive life of salinized areas couldbe extended by careful and intensive manage-ment. Current management technology, suchas drain installation or periodic flushing withlarge amounts of water, has emphasized anengineering approach. Often this is costly interms of dollars, energy, and water. Economi-cally feasible engineering approaches do noteliminate salt; they only minimize it. Therefore,some experts believe that the development ofsalt-tolerant crops would provide an importantbiological method to supplement current man-agement technologies. These plants might besuitable for land currently too saline for agri-culture, or they might be irrigated with lowerquality irrigation water, thus “saving” higherquality water for use on those plants that re-quire it.

The use of salt-tolerant organisms is not lim-ited to flowering plants. A number of programsare underway that use algae and micro-orga-nisms to produce biomass for food or energyin brackish or saltwater culture. Both indoorand outdoor systems are used. Such systemscould be used in conjunction with carbon diox-ide emissions from coal generators or salt-gradient ponds to increase productivity or togenerate solar energy (26) and would beanother way to produce agricultural productswhile using water too salty for most currentcrops.

Proponents of these technologies do not ad-vocate increasing the salinity of soil or waternor the indiscriminate use of saltwater irriga-tion. Instead they stress the need for continu-ous evaluation and careful management

ASSESSMENT

There are two approaches to developing salt-tolerant flowering plants: adding genetic salttolerance to conventional crop and forageplants or developing naturally salt-tolerant, orhalophytic, plants into productive agriculturalspecies (fig. 61).

.

Ch. IX—Technologies Affecting Water-Use Efficiency of P/ants and Animals ● 265— — -——————

Table 67.—Salt Tolerance of Crops

Salt toleranceType of crop Low Medium High

Fruit AvocadoLemonStrawberryPeach, apricotAlmond, plumPrune, grapefruitOrange, apple, pear

Vegetables . . . . . . . . . . Green beanCeleryRadish

Forages . . . . . . . . . . . . . BurnetRed clover

Meadow foxtailWhite Dutch Clover

Field Crops . . . . . . . . . . Field bean

CantaloupeDateOliveFigPomegranate

Cucumber, squashpeas, onionCarrot, potatoSweet cornLettuceCauliflowerBell pepperCabbageBroccoliTomatoMilkvetchSour clover

Meadow fescueOats (hay)Wheat (hay)

Rye (hay)Tall fescueAlfalfa, Sudan grassMountain bromeWhite sweet cloverCastor beanSunflowerFlax, cornSorghum (grain)Rice, oats (grainWheat (grain)Rye (grain)

Date palm

SpinachAspragusKaleGarden beet

BarleyWestern wheatgrassCanada wild ryeBermuda grassNuttall alkaligrassSalt grass

Cotton, rapeSugar beetBarley (grain

SOURCE” D Todd, Ground Water Hydrology 2d ed (New York John Wiley & Sons, Inc., 1980)

Halophytes

Some experts feel that the halophyte ap-proach may be more powerful since halophytesare adapted already to salty water and soil andare, in some cases, exceptionally productive (2),For example, some of these plants are moreproductive than alfalfa and grow in water atleast as salty as seawater.

Salt tolerance is scattered widely among wildflowering plants. Various halophytes are poten-tial forage crops, ornamental, potherbs, vege-tables, grains or berries (table 68). All halo-phytes are not arid- or semiarid-land plants.However, a world-wide search for promisingdesert germplasm resulted in about 1,000 ac-cessions from Argentina, Australia, Brazil,

25-160 0 - 18 : QL 3


Chile, New

Table 68.—Halophytes With Potential for Agricultural Use

Common namea Potential use Comments

Palmer’s saltgrass . . . . . . . . . Grain Used by Cocopa Indians, Gulf of CaliforniaBatis . . . . . . . . . . . . . . . . . . . . . Edible rootCord grass . . . . . . . . . . . . . . . . Forage, grain Feeds cattle, ArgentinaGlasswort 23 MTU/ha; seawater irrig.b

Salt bush Forage, grain Seed yield 1 T/ha; 16°/0 proteinCressa. . . . . . . . . . . . . . . . . . . . Animal feedMaireana Forage Feeds cattle, AustraliaMesquite . . . . . . . . . . . . . . . . . Forage Feeds livestock, 20,000 ha, ChileaScientific names are given in the appendix.bMTU/ha = metric tons per hectare

SOURCE: N. P. Yensen, M. F. Fontes, E P. Glenn, and R. S Felger, “New Salt Tolerant Crops for the Sonorhan Desert,” DesertPlants 3(3):111-118, G F Somers, “Natural Halophytes as a Potential Resource for New Salt. Tolerant Crops SomeProgress and Prospects, ” The Biosaline Concept, A. Hollaender (cd.) (New York’ Plenum Press, 1979), pp 101.105.

Zealand, Peru, and South Africa.Twenty-four species were identified from theSonoran Desert (32).

Some of these arid-land plants are known tobe useful and edible: they were gathered andeaten by native people in the past. Most, how-ever, have neither been used nor cultivated. Ex-tensive research is required before they canmake an impact on agriculture, a process thatmay take at least 50 years.

Conventional Crops

A wide variety of conventional crops is cur-rently being evaluated for variations in salttolerance. Those plants that possess unusual-ly high salt tolerances are being evaluated fur-ther. As of 1980, North American research onsuch crops occurred at seven U.S. localitiesand at least three Canadian sites. The plantsevaluated include alfalfa, cowpeas, mungbeans, melons, cucurbits,’ tomatoes, wheat, let-tuce, dates, and grapes. Israeli scientists arealso involved: they are working with tomatoes,cotton, wheat, and sugar beets, as well as fod-der and landscaping plants.

Screening for salt tolerance among only com-monly grown varieties of crop plants appearsunpromising. Much of the variability of thesecrops in salt tolerance may have been lost dur-ing breeding for other traits. Therefore, breed-ers have turned to the large seed collectionsheld in germplasm banks around the world.For example, several thousand barley andwheat accessions from USDA collections werescreened and irrigated with various dilutions

of seawater in California (13). In some cases,single species collections are not promising.Germplasm from wild relatives may be re-quired to supplement the low salt tolerance inthese plants. Because this was true of tomatoes,crosses were begun with a wild, commercial-ly useless tomato from the Galapagos Islands,

Other scientists are using tissue culture tech-niques to achieve results, a method that savesboth time and space. For example, millions ofcells, each a potential plant, can be grown ina 4-inch dish. If the dish contains salty growthmedia, only the tolerant cells will survive. Thistechnique has been used for cell lines of wheat,oats, and tobacco. Results indicate that en-hanced salt tolerance sometimes persists andcan be passed on to offspring. Experiments arealso underway on sugar beets, tomatoes, andcorn. This approach cannot be applied to allplants now, Some species cannot be culturedand regenerated yet and other species lose theircapacity for regeneration too quickly (8).

These experiments are preliminary, and itwill be some time before salt-tolerant strainsare ready for commercial use. There is anotherdisadvantage: it appears now that salt toleranceis gained at the expense of productivity,

Micro-Organisms

The cultivation of marine and brackish wateralgae is short compared to cultivation of agri-cultural crops on land. Most of the technologyis Asian; major research efforts in Westerncountries are recent. Many of the larger specieshave been cultivated in offshore beds using

Ch. IX—Technologies Affecting Water-Use Efficiency of Plants and Animals 267—————

biological breakthroughs to supplement oldertechnology. Smaller organisms, such as micro-scopic algae, blue-green algae, and bacteria, areharvested from inland ponds. The latter tech-nologies may be adaptable to arid and semiaridlands, For example, Mexico produces largeamounts of the high protein, blue-green alga,Spirulina, in large ponds and processingfacilities and Israeli scientists are experiment-ing with the same organism in brackish waterponds in the Negev Desert.

Some of these organisms can be very produc-tive in saltwater. Microalgae used in Hawaiianexperiments produced 60 tons of biomass peracre per year in small outdoor ponds. Smith

(26) speculates that such ponds would be a wayto use brine left from the process to improvesalty irrigation waters.

General concerns remain about the desirabil-ity of developing salt-tolerant crops, regardlessof the method used. It maybe futile to developsalt-tolerant forages if the plant material is toosalty for animals. Saltwater irrigation presentsother potential problems. Without intensivemanagement, ground water contaminationmay result, decreasing the quality of fresh-water, The situations in which salt-tolerantcrops provide an unusual opportunity are lim-ited. Such crops are not a panacea for the mis-management of irrigated lands.

CONCLUSIONS

A large number of opportunities to improveagriculture in arid and semiarid lands exists.Some technologies will not increase produc-tion in the usual sense. For example, the abil-ity of plants and animals to survive harsh con-ditions may sometimes be as important as highyield. Attempts to decrease total plant wateruse have often failed in the past. New ap-proaches, such as plant breeding for environ-mental stress, are more promising. The bio-technologies are blossoming with unpredict-able results. While it is clear that agricultureis changing, it is not clear how older institu-tions will adapt to these changes.

The technologies that affect water-use effi-ciency are powerful, and the choice of goalsto which they are applied is crucial. Efforts toimprove drought resistance of existing agricul-tural plants and animals is quickening. Perhapsfaster and larger gains can be made by apply-ing these technologies to “new” arid/semiaridland plants. Rich germplasm from underuseddesert crops and wild plants is available todecrease water use while maintaining agricul-tural production. Although this is an importantlong-term goal, it cannot be achieved imme-diately.

CHAPTER IX REFERENCES

1. Adams, R. P., “Chemicals From Arid/Semi-aridLand Plants: Whole Plant Utilization of Milk-weeds, ” OTA commissioned paper, draft, 1982.

2. Aller, J. C., and Zaborsky, O. R., “The BiosalineConcept, ” The Biosaline Concept, A. Hollaen-der (cd.) (New York: Plenum Press, 1979), pp.1-15.

3. Anderson, K., “Biochemical Genetics of Ribu-lose Bisphosphate Carboxylase/oxy genase: HighFrequency Transfer and Chromosome Mobili-zation by Broad Host Range R. Factors in COZFixing Bacteria, ” Genetic Engineering of Sym -

biotic Nitrogen Fixation and Conservation ofFixed Nitrogen, J. M. Lyons, et al. (eds.) (NewYork: Plenum press, 1981), pp. 249-256.

4. Austin, R. B., Bingham, J., Blackwell, R. D.,Evans, L. T., Ford, L. T., Morgan, M. A., andTaylor, M., “Genetic Improvements in WinterWheat Yields Since 1900 and Associated Phys-iological Changes, ” Journal of Agricultural SGi-ence 94:675-689, 1980.

5. Barton, J. H., “The International Breeder’sRights System and Crop Plant Innovation,” Sci-ence 216:1071-1075, 1982.

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Barton, K. A., and Brill, W. J., “Prospects inPlant Genetic Engineering, ” Science 219:671-676, 1983.Boyer, J, S., “Plant Productivity and the Envi-ronment,” Science 218:443-448, 1982.Chaleff, R. S., “Isolation of Agronomically Use-ful Mutants From Plant Cell Cultures, ” Science219:676-682, 1983.Chemical Market Reporter, Nov. 8, 1982.Donald, C. M., and Hamblin, J., “The BiologicalYield and Harvest Index of Cereals as Agro-nomic and Plant Breeding Criteria, ” Advancesin Agronomy 28:361-405, 1966.Drabenstott, M., and Duncan, M., “The CattleIndustry in Transition, ” Federal Reserve Bankof Kansas City Economic Review, July-August1982, pp. 20-33.Durzan, D. J., “Progress and Promise in ForestGenetics, ” Science and Technology . . . TheCutting Edge, Proceedings, 5t)th AnniversarySymposium Paper (Appleton, Wis.: Institute ofPaper Chemistry, 1980).Epstein, E., Norlyn, J. D., Rush, D. W., Kings-bury, R. W., Kelley, D. B., Cunningham G. A.,and Wrona, A. F., “Saline Culture of Crops: AGenetic Approach,” Science 210:399-404, 1980.Gilley, J. R., and Fereres-Castiel, E., “EfficientUse of Water on the Farm,” OTA commissionedpaper, 1982.Goodin, J. R., “Biomass Potential in Semi-aridLands, ” OTA commissioned paper, May 1982.Jefferson, T., “The Writings of Thomas Jeffer-son,” Monticello, Va., H. A. Washington (cd.),1821, j). 176.Johnson, D. A., “Improvement of PerennialHerbaceous Plants for Drought-Stressed West-ern Rangelands, ” Adaptation of Plants to Waterand High Temperature Stress, N. C. Turner andP. J. Kramer (eds.) (New York: John Wiley &Sons), 1980, pp. 179-185.Johnston, M. C., “Medicinal Plants of the South-western United States, ” Arid Land Plant Re-sources, J. R, Goodin and D. K. Worthington(eds.) (Lubbock, Tex.: International Center forArid Lands Studies, Texas Tech University),1979, Pp. 179-185.Jordan, W. R., Newton, R, J,, and Rains, D. W.,“Biological Water Use Efficiency in DrylandAgriculture,” OTA commissioned paper, 1982.Laster, D,, “Animal Performance, ” OTA com-missioned paper, 1983.LeRuduler, D., Yang, S, S., and Sconka, L., “Pro-[ine Over-Production Enhances NitrogenaseActivity Under Osmotic Stress in KlebsieZZaP n e u m o n i a , Genetic Engineering of Sym-

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biotic Nitrogen Fixation and Conservation ofFixed Nitrogen, J. M. Lyons, et al, (eds.) (NewYork: Plenum Press, 1981), pp. 173-179.Loomis, R. S., and Gerakis, P. A., “Productivi-ty of Agricultural Ecosystems,” Photosynthesisand Productivity in Different Environments, J.P. Cooper (cd.) (London: Cambridge Universi-ty Press, 1973), pp. 145-172.National Research Council, Priorities in Bio-technology Research for International Develop-ment, proceedings of a workshop, Washington,D. C., and Berkeley Springs, W. Va., J~ly 26-30,1982, Board on Science and Technology for In-ternational Development (Washington, D. C.:National Academy Press, 1982).Rains, D. W., “Salt Tolerance of Plants: Strate-gies of Biological Systems, ” The 13iosaZine Con-cept, A. Hollaender (cd. ) (New York: PlenumPress, 1979), pp. 47-67.Shepard, J. F., Bidney, D., Barsby T., and Kem-ble, R., “Genetic Transfer in Plants Through In-terspecific Protoplasm Fusion, ” Science 219:683-688, 1983.Smith, C. S., “Testimony on Potential Uses ofSaline Waters Derived From the Colorado RiverQuality Improvement Program,” U.S. Congress,Senate, hearings on Colorado River Basin Sa-linity Control Act amendments, Subcommitteeon Water and Power, Committee on Energy andNatural Resources (Washington, D, C.: U.S. Gov-ernment Printing Office), June 22, 1982, pp.185-191.Sosebee, R. E., Tueller, P. T., and Rittenhouse,L. R., “Technologies for Increasing Water UseEfficiency On-Site,” OTA commissioned paper,1982.Stoddart, L. A., Smith, A. D., and Box, T. W.,Range Management (New York: McGraw HillBook Co., 1975), 3d ed.Townley-Smith, T. F., and Hurd, E. A., “Testingand Selecting for Drought Resistance inWheat, ” Stress Physiology in Crop Plants, H.Mussell and R. C. Staples (eds.] (New York:Wiley Interscience, 1979), pp. 447-464.U.S. Department of Agriculture, “Hold theSpinach–Pass the Amaranth,” Food News forConsumers, winter 1983, p. 6.Whistler, R. L,, “Industrial Gums From Plants:Guar and Chia,” Economic Botany 36:195-202,1982,Yensen, N. P., Fontes, M. F., Glenn, E. P., andFelger, R. S., “New Salt Tolerant Crops for theSonorhan Desert, ” Desert Plants 3(3):111-118,1981,

—

Ch. IX—Technologies Affecting Water-Use Efficiency of Plants and Anirnals ● 269. -.

Appendix 9-1 .—Scientific Names of Potential “New” Agricultural Plants

Crop

Group 1:Buffalo gourd ... . . . .Cowpea . . . . . . . . . . . .Euphorbia . . . . . . . . . .Grain amaranth. . . . . .Guar ... . . . . . . . . . . . .Guayule ... . . . . . . . .Jojoba . . . . . . . . . . . . . . .Kochia . . . . . . . . . . . . . . .Mesquite . . . . . . . . . . . . .Saltbush . . . . . . . . . . . . .

Group II. Halophytes:Batis. . . . . . . . . . .Cord Grass . . .Cressa . . . . . . . . . . .Glasswort . . . . . .Maireana . . . . . . . . . . .Mesquite . . . . . . . . . . . . .Pa lme r ’ s sa l t g rass . .Saltbush . . . . . . . . . . . . .

Scientific name

Cucurbita foetidissima HBKVigna unguiculate (L.) Walp.Euphorbia spp.Amaranthus spp.Cyamopis tetragonoloba (L.) TaubParthenium argentatumSimmondsia chinensis (Link) SchneiderKochia scoparia (L.) RothProsopis spp.Atriple spp.

Batis rnaritima L.Spartina IongispicaCressa truxillensisSalicornia europaea L.Maireana brevifoliaProsopis algoroboDisfichiis palmeri (Vasey) FassettAtriplex patula, var. hastata —.

technologies affecting water-use efficiency of plants and

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