Source-sink relationship in Brassica carinata derived Brassica juncea introgression lines for improving water use efficiency under moisture deficit stress conditions

Improving water-use efficiency and seed yield stability under moisture deficit stress is a major challenge in Brassica juncea cultivation. The present study evaluated Brassica carinata –derived B. juncea introgression lines (ILs) to elucidate the role of source–sink relationships in enhancing seed yield under moisture deficit stress conditions. A set of 191 ILs, along with their parental lines, was assessed under rainfed and irrigated conditions for various agromorphological and physiological traits. Results revealed that ILs consistently outperformed parents for dry matter accumulation at maturity, seed yield per plant, harvest index, flowering duration, and reproductive-stage dry matter accumulation across environments. Under moisture-deficit stress, ILs maintained comparable crop growth rate and net assimilation rate to those of parents, while exhibiting enhanced physiological plasticity under irrigated conditions. Trait association and scatterplot analyses revealed that balanced source–sink ratio and efficient dry matter partitioning in ILs were critical determinants of seed yield under rainfed conditions. Principal component analysis further demonstrated strong multivariate associations of seed yield with crop growth rate, net assimilation rate, leaf area index, reproductive dry matter accumulation, and source–sink traits, clearly differentiating superior ILs from their parents. Several introgression lines, including IL11, IL33, IL54, IL73, IL83, IL112, IL124, IL128, IL134, IL135, IL155, IL161, and IL165, emerged as promising for moisture deficit stress conditions. Overall, the study highlights that integrating physiological efficiency with source–sink traits provides a robust framework for improving drought resilience and yield stability in Brassica juncea breeding programs through interspecific hybridization.