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The genetics of Karnal bunt (KB) resistance were studied in populations derived from crosses of four resistant stocks (HD 29, W 485, ALDAN ‘S’/IAS 58, H 567.71/ 3*PAR) and a highly susceptible cultivar, WH 542. The plant materials screened for KB response consisted of F2, BC1 and RILs from all ‘Resistant’בSusceptible’ crosses and RILs from the six possible ‘Resistant’ × ‘Resistant’ crosses as well as the parents and F1s. The screening was performed under optimal conditions for disease development with a mixture of isolates from North Western Plains of India using the widely followed syringe method of inoculation. The KB scores of the F1 from the four ‘Resistant’ × ‘Susceptible’ crosses indicated partial dominance of resistance. Genetic analysis revealed that HD 29, W485 and ALDAN ‘S’/IAS 58 each carried two resistance genes whereas 3 genes were indicated in H 567.71/3*PAR. The six ‘Resistant × Resistant’ RIL sets showed that the genes in the four resistant stocks were different and that there may be as many as nine genes governing KB resistance in the four parents. [ABSTRACT FROM AUTHOR]