Oligogenic inheritance of resistance to zucchini yellow mosaic virus in melons

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 S₇ progeny. A reciprocal cross was made between a resistant S₅ 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 F₁ plants, regardless of the direction of the cross, were resistant, indicating that the PI 414723 individual used for crossing was heterozygous. The F₂ generation obtained by self-pollination of resistant F₁ 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.