Evaluation of stay-green sorghum germplasm lines at ICRISAT

Delaying leaf senescence is an effective strategy for increasing cereal production, particularly under water-limited conditions. A set of 72 nonsenescent (stay green) genotypes of sorghum [Sorghum bicolor (L.) Moench] was evaluated for pattern of postflowering leaf senescence in replicated field experiments during the 1998-1999 and 1999-2000 post-rainy seasons at the International Crops Research Institute for Semi-Arid Tropics to identify superior sources of stay green. Individual leaves of three plants per plot were scored visually for leaf senescence at weekly intervals from flowering until harvest maturity. Leaf senescence patterns were determined by fitting logistic or linear functions to weekly percent green leaf area (% GLA), from which % GLA at 15, 30, and 45 d after flowering were estimated. On the basis of estimated % GLA at 15, 30, and 45 d after flowering in the two years, genotypes clustered into five groups. The clusters retained 74% of the total variation in % GLA, despite differences in the pattern of development of stress and subsequent leaf senescence pattern between the two years. Cluster I genotypes, which combined nonsenescence with drought escape, through early flowering, were superior to Cluster 2 genotypes, which were nonsenescent but late flowering, in the more severely stressed year when drought escape was important, but not in the milder stress year when escape was less of a factor. The experiment identified several (e.g., IS 22380, QL 27, QL 10, E36 X R16 8/1) tropically adapted lines with stay-green expression equivalent to those of the best temperate lines B 35 and KS 19.