Inheritance and Associations of Leaf, External, and Internal Pod Reactions to Common Blight Bacterium in Phaseolus vulgaris L.1

Abstract

Abstract A 6-parent Phaseolus vulgaris diallel cross was produced to determine the inheritance of leaf, external, and internal pod reactions to the bacterial pathogen Xanthomonas campestris pv. phaseoli (Smith) Dye = Xanthomonas phaseoli E.F.S. Dows (X.p.) Nebraska isolate EK-11. The parents and F1 generations were grown in the greenhouse, whereas the F2, along with parents, were also grown in the field at 2 locations (Lincoln and Scottsbluff, Neb.). The Gardner and Eberhart (1966) model, Analysis II, was used to obtain estimates of the genetic effects for the reactions to the pathogen in the different plant parts. Coefficients of variation were high in the greenhouse experiment and low in both field experiments. The increased precision of the field experiments allowed more genetic effects to be detected as being significant. The leaves of ‘Great Northern (GN) Nebraska #1 sel. 27’ and Plant Introduction (PI) 207262 were resistant, ‘Tacarigua’ moderately susceptible, and PI 163117, ‘GN 1140’, and ‘Guali’ were highly susceptible. The pods of the first 3 entries, along with ‘GN 1140’ showed moderate resistance, but the internal reaction of the pods of ‘GN Nebr. #1 sel. 27’ showed more susceptibility than the external reaction. The reaction to X.p. was quantitatively inherited in all experiments. Additive effects were primarily involved in the genetic control of the leaf, external, and internal pod reactions to X.p. Heterosis effects for leaf reaction were detected under field conditions. External and internal pod reactions were highly correlated, but little association between leaf and pod reaction was observed. It is, therefore, necessary to select for resistance simultaneously in both plant parts since correlated responses are not expected to be present. Large positive correlations were detected between the reactions of genotypes observed in the greenhouse with those in the field experiments and between the field experiments, indicating that greenhouse tests should adequately predict field performance. A significant genotype × location interaction for leaf reaction was detected, with ‘Guali’ and ‘Tacarigua’ being more susceptible at Lincoln, under higher night temperatures, than at Scottsbluff, indicating the importance of evaluating the reaction of germplasms to this pathogen in different environments.