Bacterial blight, caused by Xanthomonas campestris pv. malvacearum (Smith) Dye (Xcm), can be a serious disease in most Upland cotton (Gossypium hirsutum L.) growing areas of the world. While blight outbreaks in the USA are infrequent, serious epidemics can occur wherever susceptible cultivars are grown. The purpose of this study was to determine the bacterial blight reactions of 61 Upland cotton cultivars. This information should be useful to breeders interested in incorporating blight resistance into future cotton cultivars. Varying numbers of cultivars (including four checks) were planted each year near Perkins, Oklahoma, over a 3-yr period. The experimental design used each year was a randomized complete block with four replications. Two of the replications were used for testing cultivar reactions to Xcm Race 1. The other two replications were used for testing responses to a mixture of races. Significant differences in blight reactions were detected among cultivars each year for both Race 1 and the race mixture. Mean reactions among cultivars varied from immune to fully susceptible. Cultivars included in this study were developed in seven states. The only cultivars among them with resistance or immunity to the array of races used in this study were from Texas and Oklahoma. Cultivars developed elsewhere were moderately to fully susceptible. Large areas of the Cotton Belt will remain vulnerable to outbreaks of bacterial blight unless higher levels of resistance are more widely incorporated into breeding programs than have been in the past.
