Danin-Poleg, Y., Department of Vegetable Crops, Agricultural Research Organization, Newe ya'ar Research Center, P. O. Box 90000, Haifa 31-900, Israel
Paris, H.S., Department of Vegetable Crops, Agricultural Research Organization, Newe ya'ar Research Center, P. O. Box 90000, Haifa 31-900, Israel
Cohen, S., Department of Virology, Agricultural Research Organization, Volcani Center, P. O. Box 6, Bet Dagan 50-250, Israel
Rabinowitch, H.D., Dept. of Field and Vegetable Crops, Hebrew University of Jerusalem, Faculty of Agriculture, Rehovot 76-100, Israel
Karchi, Z., Department of Vegetable Crops, Agricultural Research Organization, Newe ya'ar Research Center, P. O. Box 90000, Haifa 31-900, Israel

The melon (Cucumis melo) plant introduction PI 414723 was observed to segregate for resistance after inoculation with a highly virulent non-aphid-transmissible strain of zucchini yellow mosaic potyvirus (ZYMV-NAT). By self-pollination of selected resistant plants, the percentage of resistant plants increased in successive generations until nearly 100% in the S 7 progeny. A reciprocal cross was made between a resistant S 5 plant of P1 414723 and a plant of the susceptible cultivar Dulce. Parental-, filial-, and backcross- generation plants were inoculated with ZYMV-NAT. One-half of the F 1 plants, regardless of the direction of the cross, were resistant, indicating that the PI 414723 individual used for crossing was heterozygous. The F 2 generation obtained by self-pollination of resistant F 1 plants segregated to resistant and susceptible in accordance with a 27:37 ratio, indicating that, in this cross, three complementary dominant genes are needed for resistance to be expressed. The resistance to ZYMV carried by PI 414723 is oligogenic with the number of genes observed to segregate in crossing depending on the genotype of the susceptible parent.