CONTRIBUTION OF OSMOTIC ADJUSTMENT TO GRAIN-YIELD IN SORGHUM-BICOLOR (L) MOENCH UNDER WATER-LIMITED CONDITIONS .2. WATER-STRESS AFTER ANTHESIS

The contribution of osmotic adjustment to grain yield in Sorghum bicolor (L.) subjected to water stress between anthesis and maturity was studied using six entries. Three of the entries (Goldrush, E57, and DK470) were selected for high osmotic adjustment and the other three (Texas 610SR, Texas 671, and SC 219-9-19-1) for low osmotic adjustment, and divided into early, intermediate and late maturity groups. Entries were either well watered, or subjected to a 50-day period of water shortage after anthesis following being well-watered prior to anthesis. Entries selected for high osmotic adjustment had mean values of osmotic adjustment at the end of the post-anthesis stress more than double those selected for low osmotic adjustment. The corresponding mean grain yield of entries with high osmotic adjustment were 24% higher than that of entries with low osmotic adjustment. The higher yield was due to both more and larger grains, and it was associated with higher harvest index and distribution index. At best, the difference in dry matter at maturity could explain only a few per cent of the difference in grain yield between entries with low and high osmotic adjustment. Water stress prior to anthesis (previous paper) reduced yield more than a post-anthesis stress of the same intensity. However, osmotic adjustment was equally effective in minimizing the reduction in grain yields in both stages. The use of osmotic adjustment as a selection trait in programs to improve the yield of grain sorghum is briefly discussed. © 1990 CSIRO. All Rights Reserved.