AN ASEXUAL VARIANT OF PHYTOPHTHORA-INSOLITA

All tested isolates of Phytophthora insolita and an unknown asexual Phytophthora species found in soil, ditch water, and diseased plant tissues in Taiwan produced ovoid, nonpapillate, nondeciduous sporangia on sporangiophores proliferating through an empty sporangium or in a nesting fashion, and formed irregular as well as spherical hyphal swellings. All tested Phytophthora isolates grew at an unusually high temperature of 39 degrees C, displayed similar or identical electrophoretic patterns of soluble proteins, and produced alpha(1) hormone. The ability of one isolate of P. insolita to produce oospores was decreased and that of another was lost completely during storage. The results suggest that all isolates of the asexual Phytophthora sp. tested were Phytophthora insolita and were unable to produce oospores owing to a defect in the physiological process of sexual reproduction.