CULTIVAR AND SPACING EFFECTS ON TRANSMISSION OF PHYTOPHTHORA-PARASITICA IN AN EBB-AND-FLOW SUBIRRIGATION SYSTEM

Phytophthora parasitica was transmitted within 6 weeks from vinca (Cat haranthus roseus) plants growing in infested potting mix, on the drain end of ebb-and-flow benches, to plants in noninfested potting mix. Tr ansmission of Phytophthora was very low when potting mix was not paste urized. When potting mix was steam pasteurized, infection of plants, d isease incidence, and severity increased with time and decreased with distance from plants in infested pots. The cultivar Pretty in Pink was more susceptible to infection by P. parasitica than cv. Peppermint Co oler, allowing more rapid and severe disease development as well as pa thogen dissemination and transmission. Pot spacing did not significant ly affect transmission of P. parasitica on an ebb-and-flow bench.