Inheritance of Resistance to Foliar Bacterial Spot of Tomato Incited by Xanthomonas campestris pv. vesicatoria

Hawaii 7998 (foliage resistant to bacterial spot) was crossed with ‘Walter’ (susceptible) and F 1 , backcross, and F 2 generations were derived. These genotypes were grown in the field at Bradenton, Fla. in the summers of 1984 and 1985 and inoculated with Xanthomonas campestris pv. vesicatoria , the incitant of bacterial spot. Disease severity for respective genotypes was similar both years, although somewhat greater in 1985. Disease severity in the F 1 was intermediate to the parents, but slightly skewed toward resistance both years. The percentage of F 2 plants with resistance comparable to Hawaii 7988 was 9.6% in 1984 and 4.6% in 1985. There was no evidence of cytoplasmic inheritance from three sets of reciprocal crosses tested in 1985. The data fit an additive-dominance genetic model, but dominance variance was negative both years, which indicates a small or negligible dominance effect. The negative dominance variance resulted in biased estimates of additive variance, narrow-sense heritability, and the number of effective factors. Nevertheless, narrow-sense heritability was moderate to high. When incorporating this resistance into new genetic backgrounds, we suggest that a modified backcrossing scheme with rigorous disease screening be used to obtain plants from homozygous resistant BCF 3 lines before crossing.