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-N AT). By self-pollination of selected resistant plants, the percentage of resistant plants increased in successive generations until nearly 1 00% in the S-7 progeny. A reciprocal cross was made between a resistan t S-5 plant of PI 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 directio n of the cross, were resistant, indicating that the PI 414723 individu al used for crossing was heterozygous. The F-2 generation obtained by self-pollination of resistant F-1 plants segregated to resistant and s usceptible 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 oligogen ic with the number of genes observed to segregate in crossing dependin g on the genotype of the susceptible parent.