Genetic control of traits related to grain filling in the common bean
A possible strategy to increase grain yield in common beans (Phaseolus vulgaris) is to obtain lines with earlier flowering and a longer grain filling period, associated with a higher dry matter accumulation rate. We examined the genetic control of these traits to investigate whether it is possible to select lines with earlier flowering, a longer period of grain formation, and a higher dry matter accumulation rate in the grain. We also sought to determine whether it would be feasible to use these traits as an indirect selection strategy for grain yield. Ten lines belonging to the Andean and Mesoamerican gene pool were crossed in a diallel scheme in Lavras, MG. The hybrids together with the parents were evaluated in a randomized block design in three seasons, corresponding to generations F2, F3 and F4. The variables measured were number of days to flowering (NDF), grain dry matter (GDM), grain yield (YIELD), number of days to physiological maturity (NDPM) and dry matter accumulation rate (RATE). We found that for NDF, NDPM and RATE, the general combining ability (GCA) explained most of the variation. Both GCA and the specific combining ability were important for YIELD. However, for this trait, the estimate of heterosis was significant, but negative (-27.7%), when the crosses involved the Andean x Mesoamerican lines. The estimated values of correlation between NDPM x NDF were positive (0.72 **), and negative between NDF x RATE (-0.52 **) and NDPM x RATE (-0.43*). Consequently, none of the populations presented potential for obtaining new lines with high grain yield, based on indirect selection for early flowering and traits associated with grain filling.