Genetical and environmental variation for resistance to bacterial blight of upland cotton

Abstract

The inheritance of resistance in Upland cotton to Xanthomonas malvacearum was investigated using a half diallel set of crosses between six inbred varieties. Parents and progeny were inoculated and examined at three sites: Shambat and Wad Medani in the Sudan, and Namulonge in Uganda. In the Sudan, leaves only were inoculated. At Namulonge leaves and bolls were inoculated and two bacterial cultures were used on the latter organs. Diallel analyses based on those developed by Hayman, Jinks and Allard were computed. Special note was taken of non-additive genetic relationships. Dominance was found to account for non-additivity, and the data were examined for interactions involving sites and bacterial cultures. The behaviour of the B7 gene was not consistent with its being a simple Mendelian locus with incomplete dominance. Genetic variances varied with inoculum, being lower with culture NCG 40 than with NCC 38. Line 4, 101-102B, contains a polygenic complex in addition to genes B2 and B3. It has outstanding resistance and could be invaluable breeding material. Progeny of 101-102B demonstrate that resistance built up by selection of minor genes can be effectively transferred.