Phenotypic assessment of sorghum (Sorghum bicolor L. Moench) germplasm reference set for yield and related traits under post flowering drought conditions KSeetharamauthorSorghum reference set collection consisting of 384 accessions of five basic races, 10 intermediate races and five wild sub species was evaluated during 2008-09 (E1), 2009-10 (E2) post rainy season at ICRISAT, Patancheru, Andhra Pradesh and during 2009-10 at UAS, Dharwad (E3- Irrigated condition and E4 – Un-irrigated condition) and RARS, Bijapur (E5- Un-irrigated condition). Data on seven qualitative and 11 quantitative traits were recorded to estimate the phenotypic diversity under post flowering drought conditions and to identify the drought tolerant accessions. The qualitative traits, white mid rib, pigmented plant, black and purple color glume, one fourth glume covered, white, purple, and brown colored seeds occurred in high frequencies in the sorghum reference set. These traits are useful markers since they are associated with economically important traits such as increased fodder quality, resistance to grain mould, preference in food and beverage industries. Variance due to genotypes (σ2g) and genotype X environment (σ2ge) interactions were significant for all the 11 quantitative characters and variance due to genotype X drought interaction was significant for panicle exerstion, panicle length, panicle width and grain yield. The seven flowering groups differed significantly for days to 50 per cent flowering and plant height. The basic races and intermediate races as group differed significantly from the wilds for panicle weight, grain yield and 100 seed weight. Grain yield of entire reference set had significant positive correlation with panicle weight, 100 seed weight but had negative correlation with days to 50 per cent flowering, plant height and basal tillers in all the environments. Principal component analysis in entire reference showed that, nine characters in E1, E2 and its pooled and eight characters in E3, E4, E5 and its pooled were important in explaining the variation. Shannon-Weaver diversity (H') index was high for plant height, 100 seed weight, grain yield, panicle weight, SPAD1 and SPAD2 in entire reference set , in all the flowering groups, basic races, intermediate races and wilds. Average phenotypic diversity index was similar in all the environments. On the basis of phenotypic dissimilarity between pair of accessions, ten pairs of most diverse accessions under drought conditions were identified. These accessions could be used in breeding programs for selecting superior lines in segregating population and for the development of mapping population. The hierarchical cluster analysis grouped five basic races, ten intermediate races and five wild sub species into three clusters in E1, E2, E4 and pooled over E1 and E2, two clusters in E3, five clusters in E5 and four cluster in pooled over E3, E4 and E5. Based on drought tolerance indices such as STI, MP, GMP, SSI, TOL and DTE a total of 65 drought tolerant accessions were indentified representing the entire reference set and seven flowering groups. Twenty nine accessions based on E1, E2 pooled and 22 accessions based on E3, E4 and E5 pooled were identified for high SCMR. Accessions identified based on drought tolerance indices and with high SCMR were predominantly from the race caudatum which was early flowering, had shortest plant height, high panicle weight and grain yield. In addition to this, best twenty accessions were identified for each of the traits, days to 50 per cent flowering, plant height, panicle length, 100 seed weight, panicle weight and high grain yield. These diverse trait specific promising accessions have the potential for their utilization in breeding programs for developing improved sorghum cultivars with a broad genetic base. The information on phenotypic diversity and trait specific accessions provided valuable baseline knowledge for further progress on the selection and breeding for drought tolerance in sorghum.Sorghum2011Tamil Nadu Agricultural University;Centre for Plant Breeding and GeneticsThesis