ABSTRACT
Our work has focused on evaluation of the role of phytoalexins in heritable resistance of cotton to bacterial blight. The most thorough studies of this type by other workers have been with fungal diseases, and mostly with isoflavonoid phytoalexins (Mansfield, 1982; Hahn et al., 1985). This study evaluates the role of sesquiterpenoid phytoalexins in a bacterial leafspot disease. Cotton (Gossypium spp.) and Xanthomonas campestris pv. malvacearum are a genetically interesting system because of the race/cultivar specificity due to a number of major host genes for resistance, each of which confers resistance to a different set of races (Brinkerhoff, 1970). The pathogen’s race phenotype is determined by avirulence genes (DeFeyter and Gabriel, 1991), each of which contains several 102-nucleotide-base-pair repeats of unknown function (D. W. Gabriel, personal communication). Upland cotton (Gossypium hirsutum L.) lines possessing several resistance genes have been developed whose resistance to bacterial blight is so high that no macroscopic symptoms or only pinpoint lesions are produced after inoculation with most races of the pathogen (Brinkerhoff et al., 1984).
