Cucurbit Genetics Cooperative Report 2:10 (article 6) 1979
Dominant Genes for Resistance to Powdery Mildew in Cucumber
H. M. Munger, Abad Morales, and Sadig Omara
Departments of Plant Breeding and Vegetable Crops, Cornell University, Ithaca, NY 14853
All reports we have seen on the inheritance of powdery mildew resistance in cucumbers have shown that any resistant parent crossed with a susceptible parent gave a susceptible F1. In the course of breeding 'Marketmore 76' with 'Spartan Salad' as the source of resistance, we observed that certain resistant plants in the F2 of the third backcross to 'Marketmore 70' gave Fl progenies with an intermediate level of resistance when they were backcrossed again to 'Marketmore 70'. Morales, in his Ph.D. thesis research, crossed 'Marketmore 70' with several plants of 'Spartan Salad' and found in the composite F1 that about half of the plants had an intermediate level of resistance that was distinctly different from the susceptibility of 'Marketmore'. Omara concentrated on this aspect of mildew resistance and tested the F1 progenies of 79 'Spartan Salad' plants which were both selfed and crossed individually with 'Marketmore 70'. Seventy-one of the progenies were uniformly susceptible, but the remaining eight had plants with distinct resistance at an intermediate level. One of the eight, plant no. 77-717, gave an F1 with Marketmore 70' with uniform resistance of about the same level as 'Poinsett'. Another, 77-730, gave an F1 with approximately half the plants showing resistance comparable to the 'Poinsett' check. The other six seemed to be segregating for a level of resistance similar to that of 'Tablegreen 65'. The inheritance of resistance from plant 77-717 is now being studied.
Another source of dominant resistance was found in PI 197088, introduced from India. This parent when crossed with 'Marketmore 70' gave an F1, with high resistance in the field and low to intermediate resistance in the greenhouse in the winter. In this hybrid, resistance tended to become lower as the plants were maturing, whereas the F1 of 'Marketmore 70' x 'Spartan Salad' 77- 717 maintained a high intermediate level of resistance throughout the plant's life and had a higher level of resistance in the greenhouse. In a genetic study of resistance, Omara found that PI 197088 carries a dominant gene for resistance, which is partially epistatic to the major gene for susceptibility found in 'Marketmore 70', 'Wisconsin SMR 18', and 'Cornell SR 5511.
A high level of resistance was found in F1s in the field when either PI 197088 or 'Spartan Salad' 77-717 was crossed with 'Tablegreen 65', 'Pixie', and 'Poinsett'.