DROUGHT STRESS EFFECTS ON THE GRAIN YIELD AND PANICLE DEVELOPMENT OF SORGHUM

Many studies have reported responses to drought stress in sorghum (Sorghum bicolor (L.) Moench) but little is known about its effects on panicle development. To determine the stage of development most susceptible to water deficiency, in terms of grain yield components, eight plants of two sorghum lines were subjected to each of 10 single, successive drought stress treatments covering the entire life cycle. In each stress treatment, water was withheld until half of the plants remained wilted at sunrise. Effects on panicle development were also studied. Single sorghum plants were grown in pots containing a 3:1 soil (Typic Argiustoll)-sand mixture in a polyethylene greenhouse at Chapingo, Mexico. Drought stress during microsporogenesis destroyed the whole panicle. Prior to this stage, drought produced abortion of the panicle-branch primordia, and a reduction of 25–55% in the number of grains per mature panicle. Later drought stress periods did not reduce the number of grains per panicle, but reduced individual grain weight by as much as 50%. Consequently, the yield was reduced by drought stress periods at all stages of panicle development before physiological maturity. Furthermore, drought stress before anthesis slowed the subsequent developmental rate of the panicle; drought stress after anthesis accelerated it. The proportion of fertile pollen grains remained above 90% in all drought stress periods. It is concluded that microsporogenesis and the milk dough stage are the most sensitive stages of sorghum panicle development to water deficits.Key words: Sorghum bicolor (L.) Moench, grain sorghum, yield components, pollen sterility, sorghum cold-tolerance, microsporogenesis