The control of bacterial blight in rain-grown cotton I. Breeding for resistance in African Upland varieties

Abstract

Projects carried out in the Lake Province of Tanganyika for breeding Upland cotton resistant to bacterial blight are described.A programme in which Albar 51 was used as resistant parent was more successful than one in which an attempt was made to transfer the major gene B6m to breeding stocks.Backcrossing was found to be of limited value as a breeding technique with rain-grown cotton, line breeding in segregating stocks being preferred.It is demonstrated that resistant types can be synthesized by the systematic exploitation of residual genetic variability in locally adapted populations.Correlations between stem, boll andleaf resistance are discussed and some deviations attributable to environmental effects described. It is inferred that there is a basic resistance mechanism in all tissues which is under the same genetic control but that results may be confused by genotype-environment interactions and by other factors operating in particular tissues.The approach to resistance breeding is discussed in relation to the evolution of resistance in African Upland cotton. It is concluded that improvement by straight selection should be given equal emphasis with improvement by hybridization in resistance breeding programmes.