Effects of certain cations on the formation and infectivity of Phytophthora zoospores. 2. Effects of copper, boron, cobalt, manganese, molybdenum, and zinc ions.
The effects of copper, boron, cobalt, manganese, molybdenum, and zinc on the production of zoosporangia by P. cinnamomi and P. drechsleri in the presence of favourable concentrations of calcium, magnesium, potassium, and iron were investigated. Copper ions were the most effective in reducing the numbers of zoosporangia formed by both fungal species. Molybdenum was also slightly inhibitory. Total inhibition of mycelial growth occurred between 1 and 5 X 10(-5) M Cu2+ whereas total inhibition of sporangial formation occurred between 1 and 5 X 10(-7) M Cu2+. At copper concentrations between 10(-5) M and 5 X 10(-7) M, many P. drechsleri zoosporangia were abnormal in appearance and nonviable. Infection of eucalypt cotyledons by P. drechsleri zoospores was inhibited by 10(-6) M Cu2+ but this inhibition was reversed by EDTA (10(-4) M). There was no evidence for interaction between Cu2+ and Ca2+, Mg2+, K+, or Fe2+ present in the solutions used in the axenic production of zoospores. Preliminary pot trials indicated that CuSO4 had a protective action for safflower seedlings to infection by P. drechsleri when CuSO4 was applied as a dilute solution over the infection period.