GENETIC-ANALYSIS OF KARNAL BUNT RESISTANCE IN 14 MEXICAN BREAD-WHEAT GENOTYPES

Fourteen Mexican genotypes of bread wheat (Triticum aestivum L.) with good to moderate levels of resistance to Karnal bunt (Tilletia indica (Mitra)) were crossed with the highly susceptible cultivar WL711 to de termine the genetic basis of resistance. The parents, F-1, F-2 and bac kcross populations of the 14 crosses were evaluated under artificial e piphytotic conditions during the 1993-94 season for Karnal bunt resist ance. The F-1 data suggested that the resistance was dominant to parti ally dominant over susceptibility. The chi(2) analysis of the segregat ion ratios in the F-2 and backcross generations indicated that the res istance in the wheat genotypes Luan, Attila, Vee# 7/Bow, Star, Weaver, Milan, Sasia and Turacio/Chil is controlled by two genes. The resista nce in genotypes Cettia, Irena, Turaco, Opata, Picus, and Yaco was fou nd to be conditioned by a single dominant gene. The genotypes with two genes for resistance expressed a higher level of resistance than thos e with a single gene and, therefore, are better sources of resistance to Karnal bunt.