Inheritance of Resistance in Three Cotton Cultivars to the HV1 Isolate of Bacterial Blight

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Abstract
Immunity to the bacterial blight pathogen, Xanthomonas campestris pv malvacearum (Smith) Dye, of cotton, Gossypium hirsutum L., has been stable for over 20 yr. A new virulent isolate of the pathogen (HV1) was identified in Africa and a cultivar (S295) resistant to all known races and isolates was subsequently developed. The objectives of this research were to determine the inheritance of resistance in ‘S295’, ‘Tamcot CAMD‐E’, and ‘Stoneville 825’ to a mixture of USA races and the HV1 isolate, and to examine the relationship between resistance at the cotyledon stage with that at the true‐leaf stage. Progenies from three crosses were artificially inoculated and disease reaction evaluated on a scale of 1 to 10. Disease grade frequency distributions indicated a single gene with complete dominance for resistance to the USA race mixture in Tamcot CAMD‐E and S295. Frequency distributions also indicated a single‐gene difference between S295 and Stoneville 825 for resistance to the HV1 isolate. Resistance in S295 to HV1 and the USA race mixture appears to be controlled by the same gene or two closely linked genes. Resistance to HV1 in S295 was inherited as a single gene, designated B12, with complete dominance for resistance. Correlations between cotyledon and true‐leaf disease grades and phenotypic ratios indicated that resistance was controlled by the same genetic mechanism at both plant stages.

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