| Summary: | Heat stress at the seedling stage can increase mortality and has become an increasing threat for Indian mustard cultivation. Indian mustard is being predominantly grown under a rainfed ecosystem. In this context, the selection of heat tolerant genotypes may be one of the panaceas. Hence, this study was planned to evolve, evaluate and identify some of the promising early maturing heat stress tolerant from a pool of advanced breeding lines, to be used as probable donors for transferring heat tolerance. For this purpose, heat stress was imposed on 10 Indian mustard advanced breeding lines at the seedling period. The mean performance of the ten advanced breeding lines of Indian mustard with respect to morphophysiology revealed that the genotype DRMRHT-13-13-5-4 recorded earliest in maturity (117.5 days), high oil content (43.14 %) and seed yield of 3182.82 (kg/ha) which was 19.75 per cent higher seed yield over best check NPJ-112 under heat stress conditions. Similarly, the genotype DRMRHT-13-13-5-6 also recorded early in maturity (118.5 days), oil content (42.18%) and seed yield of 2964.92 (kg/ha) which was 11.55 per cent higher seed yield over the best check NPJ-112. There was a positive correlation between relative water content and membrane stability index (r=0.945) but both of these traits were negatively associated with excised-leaf water loss. Cluster survey classified 10 advanced breeding lines in five divergent groups. The tree diagram revealed abundant diversity between the Indian mustard genotypes for different characters and some magnitude of a consortium between different clusters. Based on the higher membrane stability index, water retention capacity of leaves, relative water content, minimum excised-leaf water loss and seed yield, advanced breeding lines DRMRHT-13-13-5-4 and DRMRHT-13-13-5-6 were identified as early in maturity and heat tolerant at a seedling stage which could be used in breeding programmes.
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