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This study employed cotton lines developed by breeding genes for resistance to bacterial blight into the susceptible background of cultivar Ac 44. Leaves of Ac 44 and of lines containing resistance genes B2, B3, b7, or BN, or a combination of these plus a polygenic complex were each inoculated with six strains of Xanthomonas campestris pv. malvacearum. The strains included two field isolates, one from California and one from Oklahoma, neither of which was virulent against any of the four resistance genes, as judged by visible host reaction. Also included were spontaneous mutants derived from those isolates. Three of the mutants were virulent against B3 and b7 and one was virulent against BN. Final bacterial population densities were significantly lower in incompatible cultivar/race combinations than in compatible combinations (analysis of variance followed by the protected least squares difference test: P |
