INHERITANCE AND ALLELISM OF GENES FOR RESISTANCE TO RACES-1 AND 2 OF SPHAEROTHECA-FULIGINEA IN MUSKMELON

Crosses between Cucumis melo var. reticulatus lines PI 124111F, PI 124112, and PMR 6, which are resistant to powdery mildew, and Ananas-Yokneam, the universal susceptible line, were made. Crosses between each pair of the resistant lines were also made. Parents and F1, F2, BC(S), BC(R), and TC progeny plants were inoculated with either race 1 or 2 of the powdery mildew pathogen, Sphaerotheca fuliginea, in growth chambers. Segregation ratios between resistant, moderately resistant, and susceptible offspring were determined. According to the ratios obtained, PI 124112 contained two genes, the dominant gene Pm-5 and the partially dominant gene Pm-4, that conferred resistance to races 1 and 2, respectively. Resistance to races 1 and 2 in PI 124111F was conferred by the dominant gene Pm-3 and the partially dominant gene Pm-6, respectively, and resistance in PMR 6 was conferred by the dominant gene Pm-1 and the partially dominant gene Pm-2 (plus modifier), respectively. None of these resistant host genotypes carry common genes for resistance to S. fuliginea.