Effect of temperature and pH on the growth and sporulation of Phytophthora clandestina

The effects of temperature and pH on the growth and sporangial production of isolates from each of the four known races of Phytophthora clandestina Taylor, Pascoe & Greenhalgh were investigated. Mycelial growth occurred at temperatures from 10 to 30°C and pH 3.5 to 9.0 with highest growth rates of all isolates being at 25°C with a pH of 6.0–6.5. Sporangial production was greatest between 20 and 25°C and pH 5.0–7.0 with all races. However, sporulation occurred over a temperature range from 10 to 30°C and from pH 4.0 to 9.0 with all isolates. There were no consistent differences between the four pathogenic races of P. clandestina in their relative growth rate or extent of sporangial production over a range of temperatures and pH values.