Effect of calcium on the growth and virulence of Phytophthora clandestina

Abstract

Calcium was found to significantly stimulate both the mycelial growth and virulence of Phytophthora clandestina, the major soilborne fungal pathogen of subterranean clover (Trifolium subterraneum L.). On average, the addition of calcium as either CaCO₃ or CaCl₂ to 3 artificial media increased the in vitro growth of 15 isolates from 20 to 135%. Calcium was also shown to increase the severity of root disease caused by 6 isolates of P. clandestina by up to 100% in a glasshouse experiment. The addition of Ca²⁺ as CaCl₂ had a greater stimulatory effect on the virulence of P. clandestina towards cv. Woogenellup seedlings (up to 57% reduction in seedling biomass) than supplementing with CaCO₃ (maximum 36% decrease).

The virulence of 6 isolates from 3 different pathogenic races of P. clandestina were examined in the glasshouse experiment. Differences in the virulence of P. clandestina towards cv. Woogenellup seedlings was shown to be dependent on the individual isolate rather than the pathogenic race to which it is assigned.