Inheritance of resistance to bacterial blight of cotton: IV. Tanzania selections

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Abstract
Results of genetical tests in the Sudan are consistent with those of Arnold (1963), who was unable in Tanzania to transfer the bacterial blight intensifier gene, B6, as a separate entity to local cotton. Confirmation was obtained of the presence of B2 in Mwanza Local. The high resistance of UKBR selections from Mwanza Local was found to result from the interaction of B2 with a gene, or complex of genes, occupying the same locus as B6, or closely linked to it. This B6-type gene was obtained by exerting steady selection pressure over a number of years and gradually increasing resistance; it therefore reveals that during the last 50 years blight resistance in African Uplands has evolved per se. Whether all of Knight's (1957) B genes have arisen in such a way, or by point mutation, is conjectural.