Inheritance of Photoperiod Response in Andean and Mesoamerican Common Bean

In the tropics, the majority of common bean (Phaseolus vulgaris L.) landraces are photoperiod sensitive to long daylengths, yet, within certain bean gene pools, significant numbers of photoperiod insensitive cultivars are present. The effect of photoperiod response on common bean adaptation and yield potential in the tropics is not known, nor is the inheritance of photoperiod response well understood. In this study, the inheritance of photoperiod response in common beans was investigated in two environments differing in mean temperature. Five common bean lines from each of two gene pools—Mesoamerican and Andean—were crossed in all combinations within each group. Under 12.3-h natural and 18-h artificially extended daylength treatments in field studies at Palmira and Popayan, parental lines, F₁ and F₂ generations, and random F₃ lines (Palmira) were evaluated for days flower (DTF). In a second study, allelism tests were done to determine whether the genes controlling photoperiod-induced delay of flowering were the same in the Mesoamerican and Andean gent pools. The parental lines in all evaluations showed three distinct responses to long daylengths: day-neutral, intermediate, and sensitive. At Palmira, under warmer temperatures, photoperiod response was maximized with DTF ranging from 30 to 100 d. At Popayan, under cooler temperatures, photoperiod response was reduced and DTF ranged from 37 to 74 d. Neutral lines flowered about 5 d later at Popayan than at Palmira, while sensitive lines flowered about 12 d earlier. Under both environments, photoperiod sensitivity was inherited as two dominant genes (AABB), while the neutral response was conditioned by recessive epistasis (aabb or aaBB). An intermediate response occurs when the first gene is dominant, but the second gene is recessive (AAbb). All insensitive lines used in these studies were aabb, but the possible existence of insensitive aaBB genotypes is addressed. Crosses between Mesoamerican × Andean genotypes showed that the genes controlling photoperiod response in the two gene pools are the same.