Timing and Intensity of Water Deficits During Flowering and Grain‐Filling in Pearl Millet

Yields of pearl millet [ Pennisetum americanum (L.) Leeke]–a rainfed crop grown mainly on light soils in the semiarid and arid regions–are often reduced by water deficit when rains end early. The comparative response of this crop to varying intensity and timing of water deficit during flowering and grain‐filling was investigated in field experiments using a line‐source sprinkler system. The soil was an Alfisol (Udic Rhodustalf) with approximately 60 mm of plantextractable moisture. Genotypes differing in maturity were used to simulate differing timings of terminal stress. Grain yields were linearly reduced with increasing intensity of stress in all genotypes. Yield reduction rate was dependent on the time of stress onset in relation to time of flowering, as earlier‐flowering genotypes partially escaped stress. Grain number per unit area and grain size were reduced by intensity of water deficit. Grain yield and grain number, but not grain size, were affected by the time of stress onset at all intensities. Across the entire data set, stress intensity and timing accounted for 75% of the variation in measured grain yield. An advance in time of onset of stress by a day caused a 0.9% reduction in relative grain yield, compared to a 0.7% reduction in relative grain yield for each 1% additional irrigation deficit. Effects of timing of stress increased significantly with increase in stress intensity. The results emphasize the importance of timing and intensity of stress when comparing genotypes of different maturity groups using linesource gradient system, or when selecting genotypes for droughtprone environments