Further studies on the inheritance of resistance to powdery mildew of beans

Abstract does not appear. First page follows.

This paper presents the results from testing various crosses of beans (Phaseolus vulgaris L.) for resistance to powdery mildew (Erysiphe polygoni D. C.). These crosses were made between the resistant varieties Striped Hopi, Lady Washington, Hungarian, Yellow, Phaseolus vulgaris 5053, Long Kidney, Pinto, and Pink, and the susceptible varieties Robust, Small White, Kotenashi, and Red Kidney, and the semiresistant variety Long Roman.

Methods

The method of testing by inoculating detached leaflets supported on a 10 per cent sucrose solution in petri dishes as described in an earlier publieation4 has also been used in this investigation. The culture of mildew was the same single-spore strain (now designated as strain 1) used in the work previously reported. The F₁ and F₂ plants were tested in the petri dishes, the F₃ for some crosses in petri dishes and for others by field inoculation with the same strain of the mildew. Readings of the severity of mildew are given on a scale of 0-4 for the dish tests as previously described. The field readings indicate only whether the plants are resistant or suspectible. No difference was observed among the resistant varieties, and all showed complete absence of mildew; but differences were observed among the susceptible varieties, and between the susceptible varieties as a group, the resistant varieties as a group, and the semiresistant variety.

The crosses were all made in the greenhouse and most of the progenies grown in the field and in the greenhouses at the California Agricultural Experiment Station at Berkeley during the years 1933-1936. The F₃ populations of Phaseolus vulgaris 5053 × Red Kidney, Long Roman × Yellow, Long Kidney × Red Kidney, P. vulgaris 5053 × Pinto, and Long Kidney × Pinto were grown in the field at the Associated Seed Growers’ breeding grounds at Milpitas, California, in 1937.