VECTOR-ASSISTED SEED TRANSMISSION OF MELON NECROTIC SPOT VIRUS IN MELON

Seed lots prepared from fruits collected from systemically infected me lon plants were tested for seedborne melon necrotic spot carmovirus (M NSV). The hypothesis of ''vector-assisted'' seed transmission (VAST) w as tested in trials with rigorous control of the vector fungus, Olpidi um bornovanus. The vector also formed the basis for the most sensitive assays of seedborne virus, enzyme-linked immunosorbent assay (ELISA) was intermediate, and infectivity was the least sensitive assay. Altho ugh extracts of seeds not treated with acid reacted in ELISA, the assa y did not discriminate between viral antigens and infectious virus. Th e superficial viral antigens and virions were removed by acid treatmen t of seeds, bur infectious virus remained within the seed coat at leve ls not usually detectable by ELISA. Seedborne virus rarely infected se edlings unless the vector was present. confirming VAST as a novel mean s of seed trans mission that is possible because of the in vitro metho d of virus acquisition by O. bornovanus. The incidence of internally b orne MNSV ranged from 0.1 to 5.3% in the vector-based assays. In one s eed lot, MNSV was primarily on the surface of seeds, with an incidence of >50% on nontreated seeds and 0% on acid-treated seeds.