Independent Inheritance of Resistance to Race 1 and Race 2 of Sphaerotheca fuliginea in Muskmelon

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Abstract
Gynoecious Cucumis melo WI998, susceptible to powdery mildew, was stabilized for gynoecy and crossed with C. melo PI 124111F, a monoecious breeding line resistant to races 1 and 2 of Sphaerotheca fuliginea. F1 plants (all monoecious) were resistant to race 1 and moderately resistant to race 2. F2 plants (one of 16 gynoecious) segregated three resistant:one susceptible to race 1, and one resistant:two moderately resistant:one susceptible to race 2. The backcross progeny of F1 to the susceptible parent (WI998) segregated one resistant:one susceptible to race 1, and one moderately resistant:one susceptible to race 2. The backcross progeny to the resistant parent (PI 124111F) were all resistant to race 1 and segregated one resistant:one moderately resistant to race 2. The data support a monogenic, dominant inheritance of resistance Pm3 against race 1 and a monogenic, partially dominant inheritance of resistance against race 2. The symbol Pm6 is assigned to the latter gene. The two genes for resistance were not linked and no cytoplasmic (maternal) factors or modifier genes were involved in their inheritance.