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Abstract
The inheritance of resistance to Sclerotinia sclerotiorum was investigated in the diallel cross of six dry bean cultivars and breeding lines in two environments. The Gardner and Eberhart (1966) model, analysis II, revealed that variations in disease reaction were due predominantly to additive, rather than nonadditive gene action. Neither the environment x genotype, nor the environment x line interactions were significant indicating that the disease reaction was controlled by similar genetic effects, despite greater disease intensity in the greenhouse and potential for disease avoidance in the field. The Hayman (1954) graphical analysis agreed in principle with the Gardner and Eberhart (1966) analysis. The resistance to S. sclerotiorum observed in P. vulgaris is under genetic control, quantitatively inherited, and is due primarily to additive gene action.
Two field experiments were conducted to explore possible causes of inefficient selection for architectural avoidance to white mold disease in dry beans. Near isogenic lines for maturity and growth habit were blended in four pairwise combinations (5 mixture levels/blend) to determine their competitive effect on disease severity. Disease severity of an individual plant was shown to be contingent on its own maturity, as well as the maturity of its neighbors. Disease severity was not influenced by the proportion of determinate or indeterminate plants in the blend. Four different architectural types were used to study the inter-row influence of plant architecture on disease severity. Treatments were arranged as a 4 x 4 diallel. The architecture of the neighboring rows had an additive effect on disease severity, disease incidence and days to initial symptoms. The plots bordered by sprawly genotype on at least one side were infected earlier, more severely, and disease incidence was greater than the plots bordered by semi-upright genotype. The failure to obtain an accurate assessment of a genotype's performance may contribute to inefficient selection for architectural avoidance.
