INHERITANCE OF RESISTANCE TO POWDERY MILDEW (ERYSIPHE CICHORACEARUM DC) AND TO TRIFLURALIN TOXICITY IN CUCURBITA CROSSES

The inheritance of resistance to powdery mildew, Erysiphe cichoracearum DC was studied in the greenhouse and field using parents, F(,1), F(,2) and BC(,1) generations of the crosses La Primera (calabaza squash) (P(,6)) with Butternuts Ponca (P(,1)) and Waltham (P(,2)), and Ponca x Seminole Pumpkin (P(,5)). The genetics of response to trifluralin injury in field-grown direct-seeded and transplanted squash progenies derived from crosses of three trifluralin susceptible C. moschata cultivars, La Primera x Ponca and La Primera x Waltham, were also investigated. Petiole and stem reactions of plants in both field and greenhouse trials and disease reaction of leaf blades of plants in the field tests indicated that several alleles at the same locus determined powdery mildew reaction in crosses of La Primera to the two Butternut cultivars. A different recessive gene controlled disease resistance of Seminole Pumpkin (P(,5)). A quantitative inheritance pattern for the disease reaction on leaf blades was observed in the greenhouse in all crosses. Scanning electron micrographs of powdery mildew on compatible and incompatible hosts indicated that differential compatibility occurred at conidial germination. The gene for resistance in La Primera expressed multiple effects as follows: delayed conidia germination, retarded hyphal growth, shorter conidiophores and weak sporulation. Segregation for response to trifluralin in the crosses (P(,6) x P(,1)) and (P(,6) x P(,2)) supported the hypothesis that a dominant gene T determined resistance to herbicide injury but was inhibited by a dominant I-T gene. Resistant plants were designated as i-t i-t T-T or i-t i-t T-t. Seven plant introductions of the cultivated Cucurbita species resistant to trifluralin toxicity were also identified. Two complimentary dominant genes determined light-green stem color in the P(,6) x P(,1) and P(,6) x P(,2) crosses. Fruit shape was quantitatively inherited; mottle-green rind color was controlled by a single major gene and was dominant over tan fruit color in the crosses P(,6) x P(,1), P(,6) x P(,2) and P(,1) x P(,5). The information obtained from this research should be useful for the development of Butternut squash cultivars resistant to powdery mildew and trifluralin injury