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Seven previously undescribed genes in muskmelon (Cucumis melo L.) for resistance to powdery mildew [Sphaerotheca fuliginea (Schlecht. ex Fr.) Poll., races 1 and 2] are reported. Progeny 92417 has a recessive gene for resistance to race 1, which is nonallelic to Pm-1. Breeding line WMR 29 has a gene for resistance to race 1 that is allelic to the recessive gene in 92417, but it is not known whether the two genes are identical alleles. Plant introduction 414723, 92417, and WMR 29 differentiated isolates of S. fuliginea race 2 at Montfavet, France, and Riverside, Calif. Comparative responses of F1, F2, and BC progenies from crosses involving 92417, PI 414723, and WMR 29 revealed six new genes for resistance to race 2. Genetic relationships among these seven genes are not fully known. Allelic and linkage relationships of these seven genes with the five previously known genes for powdery mildew resistance are also unknown.

Lettuce (Lactuca sativa L.) cultivars and breeding lines differed in tolerance to lettuce infectious yellows virus. Correlations of symptom severity in field tests with fresh weight of control plants in a greenhouse test indicate a relationship between symptom severity and the inherent vigor of a cultivar. ‘Climax’ had the mildest symptoms and was the most vigorous cultivar. The level of tolerance exhibited by ‘Climax’ and a few other cultivars will not prevent occurrence of lettuce infectious yellows, but could ameliorate its effect on lettuce production.