Factors affecting oospore germination in Phytophthora cactorum, the incitant of apple collar rot.
Oospores of dark-grown P. cactorum cultures required light for germination. A few oospores produced under continuous light germinated in the dark, but light was required for good germination. Germination increased with increasing light intensity up to 4330 lux, and was greatest in light passing an indigo filter (440 nm) and lowest in that passing an orange filter (575 nm). Opt. temp. for germination was 20 deg C and none occurred on water agar at 28 deg , the opt. for mycelial growth. Both ageing and treatment with 1% glusulase (glucuronidase and sulfatase) increased oospore germination. It was decreased by adding CaCl2 at cons. >25 mu g/ml. Germination was not affected by agar conc., by 100 mu g/ml tergitol NPX or by 200 mu g/ml vancomycin. Germination decreased when pimaricin conc. exceeded 7.5 mu g/ml and was only 17% of the control with 100 mu g/ml pimaricin. Likewise germination was decreased 50% by 0.5% D-glucose and 1% sucrose and 40% by 200 mu g/ml polymyxin B.