Effect of Some Inorganic Salts and Hydrogen Ion Concentration on Indirect Germination of the Sporangia of Phytophthora infestclns.

Abstract

When the sporangia of Phytophthora infestans washed twice in distilled water were tested for indirect germination at 14°C, they did not germinate well (9% in 3hr) in distilled water, while in the tap water of Hokkaido Natl. Agric. Exp. Stn., they germinated well (78% in 3hr). Since some inorganic ions in the tap water appeared effective, various concentrations (0.01-10mM) of the salts, CaCl2, Ca(NO3)2, MgCl2, MgSO4, KCl, K2SO4, NaCl and Na2SO4, were evaluated for the effectiveness on indirect germination. Sporangial suspensions were preincubated for 22hr at 22°C for sporangial maturation and postincubated at 14°C for indirect germination. The most effective solution was 0.3mM CaCl2 (71% germination in 1hr), followed by 0.3mM MgSO4 (65%). Potassium and sodium salts were not very effective (<23%). At the cation concentration of 10mM all the salts except Na2SO4 inhibited indirect germination (0-5%). Hydrogen ion concentration markedly affected indirect germination, optimum at pH 8.0 (90% germination at 0.1mM CaCl2) but completely inhibitory at pH 4.5 (0%). Considering the results and the cations contained in the tap water, a synthetic salts solution favorable for indirect germination was devised: 0.2mM CaCl2, 0.05mM MgSO4, 0.05mM KH2PO4, 0.5mM NaHCO3, 0.01mM Fe-EDTA-Na. Using this solution the effect of sporangial concentration on indirect germination was also investigated. Sporangial suspensions below 2.5×104 sporangia/ml were favorable for indirect germination (≥97% in 2hr) but those above 105 were not.