Bacterial blight of cotton (Gossypium hirsutum L.) caused by Xanthomonas campestris pv malvacearum (Smith) Dye is potentially very destructive in areas where wind-driven rains or sprinkler irrigation disseminate the pathogen. Host-plant resistance offers the most economical means of controlling bacterial blight. Immunity in the USA to the bacterial blight pathogen in Upland cotton has been stable for more than 20 years. A new isolate of the pathogen, virulent on previously immune cultivars, was identified in Africa in 1981 and designated HVI. Subsequently, a breeding line (S295), with immunity to all known races and isolates of the bacterial blight pathogen was developed in Burkino Faso (formerly Upper Volta), Africa.

The mode of inheritance of resistance to the HVI isolate in the S295 line was investigated to facilitate the incorporation of resistance into susceptible genotypes. Cotyledons and true leaves of parental, F₁, F₂, and backcross progenies, from a half diallel cross of S295, Stoneville 825, and Tamcot CAMD-E, were inoculated with the HVI isolate and a mixture of USA races l, 2, 7, and 18. Disease grade distributions of segregating generations indicated the presence of a single gene with complete dominance for resistance to the HVI isolate. The genetic background, however, appears to influence the expression of this gene for resistance. When S295 was crossed with Tamcot CAMD-E, generation means analysis indicated significant additive, dominance, and digenic interaction components in the direction of resistance. Resistance to the mixture of USA races also was conferred by a single gene with complete dominance. This newly identified gene for bacterial blight resistance in S295 was designated B(12)". Pedigree or backcross breeding should be effective methods for incorporating the monogenic resistance from S295 into susceptible genotypes.