GENETICS OF VERTICILLIUM WILT RESISTANCE IN COTTON

Verticillium wilt, caused by Verticillium dahliae Kleb., is a major constraint to cotton production in almost all countries where cotton is cultivated. Developing new cotton cultivars resistant to Verticillium wilt is the most effective and feasible way to combat the problem. Little is known about the inheritance of resistance to Verticillium wilt of cotton, especially that caused by the defoliating and non-defoliating pathotypes of the soilborne fungus V. dahliae. The objective of this study was to determine the inheritance of seedling reactions to representative isolates defoliating and non-defoliating of V. dahliae in crosses of the resistant cotton Giza 45 and Tex with susceptible Albania. F1, F2, and backcross-F1 populations were inoculated to determine the mode of inheritance of seedlings by the stem-injection method. The Chi-square test for goodness of fit was used to analyse segregating populations. Two independent recessive genes appeared to control resistance of Giza 45 and Tex to both defoliating and non-defoliating pathotypes. Depending upon the cross, the two genes cumulatively condition immunity or higher levels of resistance than either parent conditioned by single gene. There was no evidence of maternal influence on the inheritance of resistance. Resistance genes in Giza 45 and Tex were recessive; therefore, breeders should consider the use of relatively large F2 populations to effectively transfer these genes to cultivars with good agronomic characteristics.