Field Crops Research, 11 (1985) 233--240 233 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

E V A L U A T I O N OF D R O U G H T T O L E R A N C E IN P E A R L M I L L E T (PENNISETUM A M E R I C A N U M (L.) L E E K E ) U N D E R A S P R I N K L E R I R R I G A T I O N G R A D I E N T

Y.M. IBRAHIM, V. MARCARIAN and A.K. DOBRENZ

Department of Plant Sciences, University of Arizona, Tucson, AZ 85721 (U.S.A.)

Contribution from the Arizona Experimental Station, Journal Article No. 3984.

(Accepted 7 March 1985)

ABSTRACT

Ibrahim, Y.M., Marcarian, V. and Dobrenz, A.K., 1985. Evaluation of drought tolerance in pearl millet (Pennisetum americanum (L.) Leeke)under a sprinkler irrigation gradient. Field Crops Res., 11: 233--240.

The responses of two selected millet (Pennisetum americanum (L.) Leeke) parents and their hybrid to different levels of water stress were studied in field experiments on a loamy sand soil in Tucson, AZ. A line source sprinkler irrigation gradient was used to create the treatments (water levels).

Dry weights were reduced significantly by water stress, with the hybrid having the highest dry weight at the low water level. The hybrid also showed higher harvest index and water efficiency at low water level. The drought tolerance index was higher for the hybrid than for the male parent. Water use efficiency was increased by stress for dry weight and decreased for yield.

Transpiration and diffusive resistance were not significantly different for parents and the hybrid at high or low water levels, but water stress reduced transpiration by 57, 56, 66% and increased diffusive resistance by 151, 148 and 294% for the female, male and the hybrid respectively.

INTRODUCTION

Pearl millet (Penniseturn arnericanum (L.) L e e k e ) i s g rown extensively in arid and semi-arid regions o f the wor ld as a d ry land crop. Millet is k n o w n to be well adap ted to condi t ions o f light soil, high t empera tu re and high solar radiat ion. Fu r the rmore , once the millet c rop has been established, a marked degree o f d rough t to lerance has been observed (Kassam and Kowal , 1975). Accord ing to Fawusi and Agboo la (1980) the observat ion tha t millet pe r fo rmed well at low soil mois ture regimes par t ly explained its ability to survive in dry ecological zones. Singh and Kanemasu (1980) s tated tha t the plant t y p e wi th (a) short to in te rmedia te height, (b) mini- m u m reduc t ion in n u m b e r o f ma ture tillers, and (c) m a x i m u m soft-water deple t ion under stress, wou ld be m o s t d r o u g h t resistant. N o r m a n and Begg

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(1968) added that the deep rooting habit enables it to withstand drought and recover deep accumulations of soil nitrate-nitrogen better than most other crops.

The sprinkler irrigation gradient system was first introduced by Hanks et al. (1976} to produce a uniform water application pattern which is con- tinuously, but uniformly, variable across the plot. This system has been successfully used with sorghum (Sorghum bicolor (L.) Moench.) (Chadhuri and Kanemasu, 1982; Garrity et al., 1982a and b, 1983; O'Neill et al., 1983}, wheat (Triticum aestivum L. em. Thell.; Hang and Miller, 1983}, dry beans (Phaseolus vulgaris L.; Miller a n d Burke, 1983), and dryland rice (Oryza sativa L.; Cruz and O'Toole, 1984) to facilitate measurement of various physiological and agronomic features over a wide range of mois- ture levels.

Being one of the most drought tolerant crops, pearl millet has great economic potential for grain product ion in the semi-arid southwestern United States. Unfortunately, there is a paucity of research on drought resistance characteristics and water stress response in millets. Much of the published research concerns the use of pearl millet as a forage crop. The primary objective of this research was to study the drought resistance characteristics and the response of pearl millet genotypes to moisture stress for both grain and forage production.

MATERIALS AND METHODS

Field studies were conducted during 1983 at the Campus Agricultural Center, Tucson, AZ, on a Brazito sandy loam soil. Two parents, 81-1014 (a female, U.S. early maturing cultivar) and Senegal bulk (a male which was selected from a bulk drought tolerance population) and their hybrid were evaluated. These were provided by W. Stegmier, Kansas State Univer- sity. The experimental design was a split plot with four replications. The genotypes were the main plots which were sown in 14 rows (14 m) parallel to, and on each side of, the gradient line. Water levels were assigned to rows (subplots) which were 4.5 m in length. Water levels were assigned as high for the two rows closest to the line source sprinkler, medium for seventh and eighth rows, and low for the thirteenth and fourteenth rows.

Seeds were planted on 26 April 1983, at rate of 120 seeds per 4.5 m plot in pre-irrigated soil, and the field was f looded to field capacity after planting and 1 week later. After emergence the field was thinned to uniform stand (10 cm between plants}. The sprinkler line was set up at the five- leaf stage. The plants were parallel to the irrigation line, so that numerous plants would be available for s tudy at each water level. Catch cans were placed at 2 m distances along all rows throughout the entire gradient. Water was measured from catch cans after each irrigation or rainfall. For all mea- surements two plants from each plot (water level} were sampled.

Physiological measurements were made at weekly intervals starting 1 week

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after stress was imposed. Measurements included the use of a Licor model LI-1600 steady state porometer to measure transpiration, diffusive resis- tance, leaf temperature and ambient temperature at eight times during the growing season.

Access tubes were placed in high, medium, and low water levels. Soil moisture was measured at four times late in the season at 30 and 60 cm depths using the Campbell Pacific Corp. Model 503 neutron probe. The samples were taken from low, medium, and high water levels. Starting the third week from emergence, plant samples were taken every other week from the high and low water level areas for dry weight analysis. At the end of the season eight plants from each treatment were harvested, and yields and dry weights were used to calculate harvest index, relative yield, drought tolerance index, and water use efficiency (kg ha -I cm water).

Harvest index was calculated as seed weight to total shoot dry weight. Relative yield of dry matter is the ratio of the grams dry weight at low water level to the grams dry weight at high water level. Drought tolerance index was obtained by relating the grain weight at low water level to that of higher water level. Water use efficiency was calculated as kilograms of dry matter or seeds in each hectare to the total amount of applied water.

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RESULTS AND DISCUSSION

Meteorological and soil moisture data

The temperatures over the growing season were average except for slightly higher temperatures in early July {Fig. 1). This was reflected by the higher than average evaporation during the season {1279 mm). Rainfall during the experimental period was only 24 mm and consequently did not affect the stress study.

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The total amounts of water applied at high, medium and low water levels were 41.26, 26.40 and 9.40 cm respectively. They were the same for the three germplasm sources. Soil moisture at the first depth (30 cm) was higher for the female parent than for either the male parent or the hybrid, bu t otherwise there were no differences among mainplots (Fig. 2). The female parent grew slower and extracted less water during the season than the other genotypes (Figs. 2 and 3). Plant dry weight at the high water level showed a clear exponential phase of growth with the hybrid reaching about 140 g towards the end of the season (Fig. 3). However, at the low water level growth was reduced significantly, with the hybrid again having the highest dry weight of only just above 60 g (Fig. 3). There were no significant differences between entries at low water level for harvest index. However, at high water levels the female parent was significantly different from the other two entries (Table 1). For the three entries, water stress reduced the harvest index significantly. The relative yield of the dry matter was higher for the male and hybrid than for the female. The hybrid had the highest drought tolerance index (0.04), followed by the male parent (Table 1).

TABLE 1

Measured and calculated parameters for three millet entries grown under a sprinkler gradient line in 1983

Entries Water treatment

High Low

Rela- Drought tive tolerance yield index

Total Seed Harvest Total Seed Harvest Dry shoot weight index shoot weight index matter dry per dry per weight plant weight plant (g) (g) (g) (g)

Grain

Female 113.38a 5.56a 0.05a* 32.87a 0.01a 0.0003a* 0.29 0.002 81-1014

Male 106.50a 25.44b 0.24b* 48.13a 0.08a 0.0020a* 0.45 0.003 Senegal Bulk

Hybrid 142.75a 27.09b 0.19b* 62.87a 1.11a 0.0200a* 0.44 0.040 81-1014 × Senegal Bulk

Means followed by the same letter w i th in each column are not significantly different at the 5% level according the SNK Method. *Treatment means l isted horizontally are significantly different at the 5% level according to the SNK Method.

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Water use efficiency

Water use efficiency (WUE) for total dry matter was increased with water stress for the three entries (Table 2). However, when calculated on the basis of grain yield there was a decrease in WUE with stress (Table 2). These findings agreed with those of Singh and Kanemasu ( 1 9 8 0 ) w h o found reduced WUE for grain yield under no irrigation; and Garrity et al. (1982) who found a strong negative t rend in WUE with water stress. Water use efficiency at low water level was higher for the hybrid for both yield and dry mat ter (Table 2).

TABLE 2

Water use efficiency (WUE) (kg ha -~ cm) for three millet entries grown under sprinkler gradient line in 1983

Entries Water Final dry Grain yield WUE treatment matter plant -1 plant -1

(g) (g) Total dry matter Yield

Female H i g h 113.38a 5.56a 359.94 17.65 81-1014 Low 32.87b 0.01c 104.35 0.03

Male H i g h 106.50a 25.44b 330.10 80.76 Senegal Low 48.13b 0.08c 152.79 0.25 Bulk

Hybrid H i g h 142.75a 27.09b 453.17 86.00 80-1014 X Low 62.87b 1.11d 199.59 3.52 Senegal Bulk

Means followed by the same letter within each column are not significantly different at the 5% level according to the SNK Method.

Transpiration, diffusive resistance, temperature

There was no significant difference between the parents and hybrid at high or low water level for transpiration and leaf diffusive resistance but there was a significant difference between high and low water levels for each entry (Table 3). Stress reduced transpiration by 57, 56, and 66% for the female, male, and hybrid, respectively. Stress increased diffusive re- sistance by 151, 148, and 294% for the female, male, and hybrid. There was no significant difference between high and low water for each entry for leaf temperature. The female had the highest transpiration at both high and low water levels (Table 3).

It is concluded that the hybrid had the highest dry weight, harvest index, and water use efficiency at low water level. The hybrid also showed a higher drought tolerance index and a larger increase in leaf diffusive resistance than the other genotypes.

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TABLE 3

Means of physiological parameters taken at weekly intervals for three millet entries grown under a sprinkler gradient line in 1983

Entries Water Transpiration Leaf Leaf diffusive level temperature resistance

(pg cm -2 s-') (°C) (s cm -I)

Female High 12.49a 35.13a 4.65a 81-1014 Medium 7.16 36.53 11.01

Low 5.33b 36.58a 11.66b

Male High 10.24a 35.41a 5.72a Senegal Medium 7.42 36.67 10.57 Bulk Low 4.55b 36.81a 14.21b

Hybrid High 11.14a 35.44a 4.62a 81-1014 × Medium 7.61 36.44 11.96 Senegal Low 3.75b 37.42a 18.20b Bulk

Means followed by the same letter within each column are not significantly different at the 5% level according to the SNK Method.

ACKNOWLEDGEMENT

Th i s r e s e a r c h was f u n d e d in p a r t b y t h e S o r g h u m / M i l l e t T i t l e X I I C R S P ( I N T S O R M I L ) .

REFERENCES

Chadhuri, U.N. and Kanemasu, E.T., 1982. Effect of water gradient on sorghum growth, water relations and yield. Can. J. Plant Sci., 62: 599--607.

Cruz, R.T. and O'Toole, J.C., 1984. Dryland rice response to an irrigation gradient at flowering stage. Agron. J., 76: 178--183.

Fawusi, M.O.A. and Agboola, A.A., 1980. Soil moisture requirements for germination of sorghum, millet, tomato, and celosia. Agron. J., 72: 353--357.

Garrity, D.P., Watt, D.G., Sullivan, C.Y. and Gilley, J.R., 1982a. Moisture deficits and grain sorghum performance: evapotranspiration--yield relationships. Agron. J., 74: 815--820.

Garrity, D.P., Walter, D.G., Sullivan, C.Y. and Gilley, J.R., 1982b. Moisture deficits and grain sorghum performance: Effect of genotype and limited irrigation strategy. Agron. J., 74: 808--814.

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Hang, N. and Miller, D.E., 1983. Wheat development as affected by deficit, high fre- quency sprinkler irrigation. Agron. J., 75: 234--239.

Hanks, R.J., Keller, J., Rasmussen, V.P. and Wilson, G.D., 1976. Line source sprinkler for continuous variables irrigation--crop product ion studies. Soil Sci. Soc. Am. J., 40: 426--429.

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Kassam, A.H. and Kowal, J.M., 1975. Water use, energy balance and growth of Gero millet at Samaru, northern Nigeria. Agric. Meteorol., 15: 333--342.

Miller, D.E. and Burke, D.W., 1983. Response of dry beans to daily deficit sprinkler irrigation. Agron. J., 75 : 775--778.

Norman, M.J.T. and Begg, J.E., 1968. Bulrush millet (Pennisetum typhoides) (Burm.) S. and H . ) a t Katherine, N.T.: A review. J. Aust. Inst. Agric. Sci., 6: 59---68.

O'Neill, N.K., Hofmann, W., Dobrenz, A.K. and Marcarian, V., 1983. Drought response of sorghum hybrids under a sprinkler irrigation gradient system. Agron. J., 7 5 : 1 0 2 --107.

Singh, P. and Kanemasu, E.T., 1980. Soil water, plant water and temperature relation of millet (Pennisetum americanum (L.) Leeke) and their relationship to crop yields. Third Annu. Rep. Improvement of Pearl Millet, Manhattan, KS, 66506: 75--93.