Genetic Variability and Effect of Postflowering Drought on Stalk Sugar Content in Sorghum Mini Core Collection

Sweet sorghum [Sorghum bicolor (L.) Moench] is an important food, feed, and biofuel crop worldwide. Its stalks are rich in sugar, largely influenced by environments and crop stage when the stalks are harvested. This study evaluated sorghum mini core collection for stalk sugar content on the basis of Brix, phenology, and agronomic traits. Accessions were first classified into five groups based on flowering to match crop phenology, which together with controls were separately grown in split-plot design in vertisol under irrigated and drought stress conditions for two postrainy seasons. The main and interaction effects were significant for most of the traits. Drought stress significantly increased the mean Brix (12.11 to 26.76%) in four of the five groups of accessions. The mean Brix increased under drought in 169 accessions, decreased in one accession, while the remaining accessions were not affected. IS 13294, 13549, 23216, 23684, 24139, 24939, and 24953 significantly recorded greater mean Brix (14.0 to 15.2%) as compared with best control, IS 33844 (12.4%), across environments. However, these accessions had lower yields and lower 100-seed weight. In contrast, IS 1004, 4698, 23891, and 28141 significantly outyielded IS 33844 by 11.7 to 22.7% and had almost the same Brix content (similar to 13%). A hierarchical tree diagram grouped these accessions into two distinct clusters: accessions with significantly greater Brix but lower yield and those with high yield but with Brix similar to IS 33844. The grouping also separated accessions largely on the basis of geographic regions and racial classification. The identified accessions are ideal resources for the development of cultivars with bioenergy traits.