GENETICS OF HEAT TOLERANCE DURING REPRODUCTIVE DEVELOPMENT IN COMMON BEAN

Common bean (Phaseolus vulgaris L.) is grown in regions where high temperatures during reproductive development reduce yields. The purpose of this study was to identify sensitive growth stages during reproductive development and to investigate the genetics of heat tolerance during these stages. Exposure to high temperatures during two reproductive growth stages, namely flower bud formation and pod filling, resulted in particularly severe damage. This damage was evaluated by scoring two corresponding traits-flower bud abortion and reduced pod fill. For each trait, two tolerant and two susceptible large-seeded dry bean genotypes were chosen and crossed in all combinations, including reciprocals. The parents and control cultivars were evaluated under heat stress conditions at two locations in the Central Valley of California; this allowed us to determine that genotype x environment interactions were present for both traits. Genetic studies included parents, F-1 and F-2 progenies, and control cultivars at one of the above locations. Both traits displayed continuous variation, indicating quantitative inheritance. Generation means analyses demonstrated that additive genetic effects were significant for both heat tolerance traits, but were more important for tolerance to bud abortion. Significant dominance effects for tolerance to bud abortion were attributed to either linkage or pleiotropy of the single dominant gene conferring indeterminate growth habit. Both generation means and diallel analyses demonstrated the presence of cytoplasmic effects including interactions of cytoplasmic with nuclear genes. The significant additive effects observed indicate that gain from selection for improved heat tolerance should be possible for both traits.