Euphytica 29 (1980) 155-160

EVALUATION OF W INTER WHEAT CULTIVARS FOR DROUGHT RESISTANCE’

G. B. ADJEI and M. B. KIRKHAM’

‘Department of Agronomy, Oklahoma State University, Stillwater, Oklahoma 74074, USA

Received 2 May I979

INDEX WORDS

Triricum aestivum L. em. THELL., winter wheat, drought resistance, evaluation, leaf water potential, stomata1 resistance.

S U M M A R Y

Cultivars of winter wheat (Triticum aestivum L. em. THELL.), considered by wheat breeders to be drought sensitive or drought resistant, were grown under two irrigation regimes (daily or weekly waterings) to determine physiological responses to drought and to evaluate methods to use in screening for drought resistance. Leaf water potential, stomata1 resistance, plant resistance to water flow, and soil water potential were measured for three weeks on vernalized plants in a growth chamber. When water was lacking, drought- sensitive plants had a lower leaf water potential than did drought-resistant plants. With both daily and weekly waterings, stomata1 resistance was higher in drought-resistant plants than in drought-sensitive plants. Plant resistance to water flow, calculated as the difference between the soil water potential and leaf water potential divided by the amount of water used by the plant, was usually higher in drought-resistant plants than in the drought-sensitive plants. The results showed that, when screening for drought resistance% stomata1 resistance was a better method to use than determinations of leaf water potential or plant resistance to water flow.

INTRODUCTION

The major environmental factor lim iting the range of adaptation for wheat (Triticum aestivum L. em. THELL.) is drought. Wheat yields could be enhanced if wheat genotypes could be grown in areas now too dry to support wheat growth during part or all of the growing season. Drought during the early part of the life cycle is a severe problem in many wheat-growing regions. For example, in the High Plains of the USA, wheat often is ‘dusted-in’. Farmers hope enough rain will come to sustain growth. It often does not and crops fail because the young plants cannot withstand the dry conditions. Wheat genotypes need to be identified which are tolerant of drought during early plant growth.

More wheat is produced annually than any other food or feed crop (JOHNSON, 1977). Yet information about drought resistance of wheat is lacking. Wheat breeding pro- grams have been based on selection for yield by itself rather than physiological charac- ters which control yield (DONALD, 1968). Studies which do consider physiology usually have been done with no drought stress (FISCHER, SANCHEZ & SYME, 1977). Almost no experimental work has been carried out with different wheat cultivars grown under dryland conditions, even though wheat breeders have long noted that certain cultivars ‘Journal article 3578 of the Agricultural Experiment Station, Oklahoma State University. Work was partially supported by a Grant-in-Aid of Research from Sigma Xi, The Scientific Research Society of North America, to the senior author.

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G. B. ADJEI AND M. B. KIRKHAM

are more drought resistant than others. Therefore, the objectives of the research reported herein were to: 1) determine physiological response to drought, during the early part of the growth cycle, of wheat cultivars commonly grown in the semi-arid winter-wheat belt of the USA and 2) evaluate physiological methods which plant breeders can use to screen cultivars for drought resistance.

MATERlALSANDMETHODS

The cultivars of hard red winter wheat (Triticum aestivum L. em. THELL.) used in this study,andtheirdroughtresistance (SCHLEHUBER& YOUNG, 1955; TODD &WEBSTER, 1965; personal communicat ions from F. C. Petr and E. L. Smith) were as follows: Drought resistant: ‘Concho’, ‘Tascosa’ Intermediate: ‘Osage’, ‘Scout 66’, ‘Improved Tr iumph’ Drought sensitive : ‘Centurk’

Certified seeds were planted on 14 November 1977 (day I), germinated in white silica sand, vernalized in a refrigerator for 50 days, and transferred to a growth chamber (Sherer Mode l CEL 37-14) set at 25°C day and 20°C night with a 12-hour photoperiod from 0700 to 1900 hours. The flux density of incident light, provided by a combination of f luorescent and incandescent lamps, was 635 u Einsteins m-2sec-1. The relative humidity varied from 42 to 68%.

The vernalized plants were grown in plastic pots (10 cm diameter, 10 cm height; four seedl ings per pot) which contained 540 g sterilized, sieved (U.S. standard size no. 10 mesh, 2000 m icron openings) soil (AP horizon of a Kirkland silt loam, classified as a Udertic Paleustoll; GRAY & ROOZITALAB, 1976). Vermiculite was placed on the soil to m inimize evaporation. The plants were 71 days old when measurements started on January 23, 1978, and cont inued through February 10, 1978.

During the measurement period, half the plants were watered daily with 80 m l tap water and half with 120 m l tap water once a week. On the days that the weekly-watered plants received water, 100 m l extra water was added to the daily-watered plants. Pots were weighed daily. Leaf water potentials were taken every three days before watering (16: 00 h) using an in situ leaf hygrometer/psychrometer (Wescor Sensor L-51A con- nected to Wescor HR-33T Dew Point M icrovoltmeter, Wescor, Inc., Logan, Utah, USA) (CAMPBELL & CAMPBELL, 1974). Stomata1 resistance readings of the lower surface of leaves were taken daily before watering using a diffusion porometer (LI- COR LI-65 Autoporometer and LI-20s Diffusion Resistance Sensor, Lambda Instru- ments Corp., Lincoln, Nebraska, USA) of the type described by KANEMASU et al. (1969). Soil water potentials were taken daily before watering with soil psychrometers (Model PT-5 1, Wescor, Inc., Logan, Utah) connected to a m icrovoltmeter (Model MJ- 55, Wescor, Inc., Logan, Utah).

RESULTSANDDISCUSSION

Results for Concho, a drought-resistant cultivar, and Centurk, the drought-sensit ive cultivar, will be contrasted. Tascosa, the other drought-resistant cultivar, did not survive the vernalization treatment. Results for Osage, Scout 66, and Improved Tri- umph were intermediate between those for Conch0 and those for Centurk.

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DAYS AFTER PLANTING

WATERED WEEKLY

-401 I

Fig. 1. Soil and leaf water potentials of two cultivars of winter wheat irrigated daily with 80 ml water or weekly with 120 ml water. Centurk is drought-sensitive and Conch0 is drought-resistant. Arrows indicate days weekly watered plants were watered and 100 ml extra water was added to daily-watered plants. Vertical l ines show standard deviations. Only half the standard deviation line has been drawn to avoid cluttering the figure.

Potentials. Figure 1 shows the soil water potential and leaf water potential of Conch0 and Centurk under the two irrigation regimes.

For the daily-watered plants, the soil dried slightly (from -1.5 to -3.0 bars) during each irrigation cycle. Soil potentials rose to -1.5 bars when the 100 ml extra water was added weekly to the daily-watered plants. The small drop in soil water potential resulted in a large drop in leaf water potential during the second drying cycle (between waterings on days 76 and 83) which indicated that, even with daily waterings of 80 ml,

01 ’ 72 76 80 84 88 DAYS AFTER PLANTING

Fig. 2. Stomata1 resistance of two cultivars of winter wheat under two irrigation regimes. For experimental conditions, see legend of Fig. 1.

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G. B. ADJEI AND M. B. K lRKHAM

5 0 CONCH0 WHEAT, DROUGHT RESISTANT

WATERED WEEKLY

DAYS AFTER PLANTING

Fig. 3. Plant resistance of two cultivars of winter wheat under two irrigation regimes. For experimental condit ions, see legend of Fig. 1.

the plants were under some stress. The leaf water potential of Centurk was lower than that of Conch0 (-25.5 vs. -18.8 bars, day 83, F ig. 1). After adding the extra water (100 m l) to the daily-watered plants on day 83,‘the soil water potential rose again to -1.5 bars, but the leaf water potential of both cultivars remained low (-20.8 bars for Concho, -24.3 bars for Centurk, day 86, F ig. 1) until day 89.

For the weekly-watered plants, the soil water potential fell during each drying cycle (from about -2 to -7 bars between days 71 and 75; from -1.5 to -8 bars between days 77 and 82; and from -1.5 to -6 bars between days 85 and 89, F ig. 1). Leaf water potential of both cultivars remained constant during the first drying cycle. After the second drying cycle, the leaf water potential of Centurk was lower than that of Conch0 (-32.5 vs -25.5 bars, day 83, F ig. 1). Leaf water potential rose after rewatering on day 83, but not to values observed at the beginning of the experiment.

Stomata1 resistance. F igure 2 shows the stomata1 resistance of the two cultivars of wheat under the two irrigation regimes.

For the daily-watered plants between days 77 and 86, the drought-resistant cultivar had a significantly higher stomata1 resistance than that of the drought-sensit ive cul- tivar. The drought-resistant plants closed their stomata in response to the slight stress in the soil (Fig. l), while the drought-sensit ive plants kept their stomata open.

For the weekly-watered plants between days 81 and 85, the drought-resistant cul- tivar had a significantly higher stomata1 resistance than that of the drought-sensit ive cultivar. The stomata1 resistances of both cultivars increased during each drying cycle and then fell after rewatering. However, values did not fall to those observed at the beginning of the experiment. At the end of each drying cycle, stomata1 resistance values were higher than those at the end of the previous cycle, except for Centurk which had similar values at the end of the first and second drying cycles (30 set/cm, days 75 and 82, F ig. 2).

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Plant resistance. If one assumes water flow through the plants is proportional to the potential difference between the root med ium and the leaf water potential, an apparent total plant resistance, R, can be calculated for the root, stem, and leaf using AJl/Aw - R, where A@ is the difference between the soil water potential and leaf water potential and Aw is the amount of water lost from the pots over a specified time period. Using the values in F ig. 1 for soil and leaf water potentials and those obtained from daily weighings of pots (data not shown), values for the plant resistance, R, can be estimated (Fig. 3).

Conch0 general ly had a higher plant resistance, as well as a higher stomata1 re- sistance (Fig. 2) than did Centurk, except on day 83 for the weekly-watered plants when Centurk had a high plant resistance. On this day, the leaf water potential of Centurk fell (see F ig. 1). However, the amount of water it lost did not change much between days 79 and 83 (the stomata1 resistance remained relatively constant -see F ig. 2). Because A$ became large and Aw did not change to a great extent, total plant resistance, R, for Centurk was large on day 83. Total plant resistance was not as good an indicator of drought resistance as was stomata1 resistance because the R for Conch0 was not always greater than the R for Centurk. The stomata1 resistance of Conch0 was consistently higher than that of Centurk (Fig. 2).

O ’TOOLE & CHANG (1978) of the International Rice Research Institute in the Philip- pines feel that evaluation of stomata1 behavior as an indicator of drought stress or as a tool for screening for drought resistance is problematic. They say, ‘The dynamics of stomata1 resistance and the variability in the environmental factors that contribute to drought make the development of mean ingful and repeatable screening procedures difficult. Stomata1 resistance appears remote as a general selection criterion for drought resistance in rice.’ However, SHIMSHI & EPHRAT (1975) who worked with up to 11 cultivars of spring wheat grown under field condit ions in Israel, suggested that the porometer method would be useful in wheat breeeding programs. The results of our experiment corroborate the suggest ion of Shimshi and Ephrat. Concho, the drought- resistant cultivar, had a higher stomata1 resistance than did Centurk, the drought- sensitive cultivar.

CONCLUSlON

Under lim ited-water conditions, leaf water potential of drought-sensit ive plants of hard red winter wheat was lower than that of drought-resistant plants. Drought- sensitive plants had a lower stomata1 resistance than drought-resistant plants. The total plant resistance to water flow, calculated as the difference between the soil water potential and leaf water potential divided by the amount of water used, was usually higher in drought-resistant plants. Stomata1 resistance was a better indicator of drought resistance than was the total plant resistance. The study showed that stomata1 resistance was the best method to use to screen plants for drought resistance.

ACKNOWLEDGEMENTS

W e thank Frank C. Petr, Area Agronomist, Texas Agricultural Extension Service, The Texas A&M Univ. System for supplying the seed ; Dr Ronald W . McNew, Oklahoma

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State Univ., for statistical help; Glenn H. Hartman in charge of the Controlled Environment Research Laboratory, Oklahoma State Univ., for technical help; and Dr E. L. Smith, wheat breeder, Oklahoma State Univ., for information concerning the cultivars used in the study.

REFERENCES

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DONALD, C. M., 1968. The breeding of crop ideotypes. Euphytica 17: 385-403. FISCHER, R. A., M. SANCHEZ & J. R. SYME, 1977. Pressure chamber and air flow porometer for rapid field

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