Evaluation of heterotic effects and inbreeding depression of F2 populations of Brassica juncea based on yield and yield-contributing traits

Indian mustard is recognized as a resilient and economically important oilseed crop. However, its potential remains untapped due to the limited availability of short-duration, high-yielding varieties capable of outcompeting other rabi crops. Considering this notion, we have evaluated twenty-one F₂ and six BC₁F₁ populations derived from seven diversified parents of Brassica juncea following a Randomized Complete Block Design at Sher-e-Bangla Agricultural University. Based on key agronomic traits, the genetic components, heterosis, inbreeding depression, and gene action were studied to select early maturing and high-yielding populations. The percentage of heterosis was manifested in various cross-combinations, including P4 ​× ​P6 (91.45% for yield per plant) and P5 ​× ​P6 (28.52% for thousand seed weight), emerging as promising candidates for increasing productivity while managing negative inbreeding effects. Conversely, significant inbreeding depression was noted in traits like days to siliquae maturity and yield, particularly in crosses, P1 ​× ​P2 (6.29%) and P3 ​× ​P5 (21.74%), underscoring the need for careful selection in breeding programs to mitigate these effects. Variance analysis indicated that both additive and non-additive genetic interactions play a pivotal role in the inheritance patterns of the traits of interest. Among the six backcrosses, one promising line was (P5 ​× ​P6) ​× ​P5, demonstrating early maturity (107.00 DAS) with improved seed yield (12.47 ​g). This combination exhibited the potential for enhancing the adaptability and productivity by maintaining the maturity index and accelerating yield. Furthermore, significant phenotypic variation across yield-contributing traits was notable, whereas thousand seed weight and yield per plant showed high broad-sense and narrow-sense of heritability. Besides, positive correlations between seed yield and its attributing traits were noted, suggesting potential avenues for selection breeding. Collectively, the obtained findings enhance the understanding of genetic mechanisms underlying heterosis and inbreeding depression in B. juncea, providing insights and effective strategies for developing superior cultivars with optimized agronomic traits.