Combining Ability and Gene Action Controlling Chocolate Spot Resistance and Yield Traits in Faba Bean (Vicia faba L.)

Chocolate spot disease devastatingly impacts faba bean growth and productivity. Thenceforth, genetic study of chocolate spot resistance and yield traits is crucial to conceive appropriate strategies for breeding and sustaining faba bean production particularly under abrupt climate change and a fast-growing global population. The current study was performed to identify promising resistant and high-yielding progenies, to study the mode of inheritance for chocolate spot resistance and yield traits using half-diallel mating design, and to investigate the association between seed yield and its attributes traits under conditions of chocolate spot disease. Two resistant (Nubaria-1 and Sakha-1) and two susceptible (Tribe-White and Camolina) parents previously characterized were used to generate six F1 hybrids which were selfed to produce F2 progenies. The parents and their F1 and F2 were evaluated at hot-spot location for chocolate spot disease. Significant variation was detected for chocolate spot resistance and yield traits among the evaluated parents and their cross combinations in both generations. The general (GCA) and specific (SCA) combining ability effects were highly significant for chocolate spot severity and yield traits in both generations. From the results, it is noteworthy that the cross combinations of P1(Nubaria-1)×P2(Sakha-1), P1×P4(Camolina) and P2×P3(Tribe-white) displayed the highest seed yield per plant in the F1 generation (155.66, 199.96, and 147.96 g respectively) as well as the F2 generation (172.36, 123.06, and 119.80 g respectively) simultaneously with high resistance to chocolate spot. Consequently, these crosses could be promising combinations for increasing seed yield, and resistance to chocolate spot in breeding programs of faba bean. The additive gene effect was predominant for chocolate spot resistance, plant height, days to flowering, number of branches per plant and 100-seed weight in both generations. Accordingly, selection could be effective to improve these traits in early generations. By contrast, the non-additive gene effects were preponderant for seed yield per plant, number of seeds per plant and number of pods per plant. This suggests the importance of transgressive segregation for improving these traits through breeding programs. While selection for improving these traits could be less effective in the segregated generations which should be postponed to advanced generations. A strong positive association was identified between seed yield per plant and each of number of branches per plant, 100-seed weight, plant height, days to flowering, number of pods per plant and number of seeds per plant. This signifies their significance as vital attributes for indirect selection, especially in the early generations due to their ease of evaluation in comparison with seed yield. On the contrary, linear regression analysis revealed a steeply inverse relationship between seed yield and chocolate spot disease in both generations.