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Abstract
Common blight in beans (Phaseolus vulgaris L.) incited by Xanthomonas campestris pv. phaseoli (Smith) Dye (X c p) reduces crop yield and seed quality. The objective of this experiment was to study heritability and phenotypic correlations of the disease reaction to various strains of X c p at several plant developmental stages in specific bean crosses using diverse methods of inoculation. Leaf and pod disease reactions to strains of X c p were inherited quantitatively and narrow-sense heritability estimates were low in the following crosses between Phaseolus vulgaris cultivars/lines: Bac-6 (moderately resistant = MR) × NE-EP1 (MR); Bat-862 (MR) × ‘Pompadour Checa’ (susceptible = S); ‘Pompadour Checa’ (S) × Bac-6 (MR); ‘Venezuela 44’ (S) × Bat-862 (MR). Pod disease reaction was not correlated with leaf disease reaction at any growth stage. Low or nonsignificant phenotypic correlations were detected between disease reactions of leaves at the seedling and flowering stages with the several methods of inoculation. Intermediate phenotypic correlations were found for disease reactions with three methods of inoculation at the seedling stage, but only with two methods in the flowering stage. Negative or nonsignificant phenotypic correlations were observed between leaf disease reaction and number of days to first flower. Different duplicate recessive genes were found to control two foliar abnormality traits: crippled growth and variegated leaves. No plants with a combination of both traits were observed. An association was found between crippled growth and a high level of resistance to strain V3S8 of X c p in the cross Bat-862 × ‘Pompadour Checa’.
Abstract
Common blight in beans (Phaseolus vulgaris L.), incited by Xanthomonas campestris pv. phaseoli (Smith) Dye, is a serious seedborne disease in various parts of the world. We tried to detect possible differences in seed infection and transmission of bacteria in selected bean cultivars/lines. Dry seeds, flower buds (24 to 36 hr before anthesis), small pods (2 to 3 days old), and green seeds of individual plants of Bac-6, ‘Venezuela 44% ‘Pompadour Checà’ dry beans, and of dry seed of Great Northern (GN) ‘Tara’ were examined for possible internal infection after inoculating the seeds, seedlings, and plants with common blight bacterium at various sites. Inoculation of the pedicels of the flower buds and small pods resulted in transmission of the bacteria through the vascular tissue of the pod to the seeds, causing internal infection without any external symptoms shown either by the pods or seeds. Bac-6 was resistant to seed infection, and ‘Venezuela 44’ was most susceptible, followed by ‘Pompadour Checà’ and GN ‘Tara’. Planting infected seeds did not result in a systemic transmission of the bacteria in the vascular tissue of the plants to the seeds. Infected leaves were likely to be the main source for the external infection of pods, which could lead to internal and/or external seed infection. Breeding for resistance to seed infection and transmission of bacteria should aid the control of this disease. A useful technique for assessing internal infection of seeds with the bacteria was developed.