Physiological studies on Phytophthora infestans (Mont.) de Bary

Abstract

The purpose of the present experiments was to make clear the nutritional requirement for the sporulation of Phytophthora infestans on the artificial culture.Most of the work to be described has been carried out with the use of isolates H1 and H3 of P. infestans, the first being isolated in 1954 from the naturally infected leaf of potatoes of the variety Irish Cobbler and the second in 1954 from Kennebec at Kotoni in Hokkaido.The experimental results obtained may be summarized as follows.1. P. infestans produced the highest number of sporangia on the bean-meal agar of the following formula: 50g ground dry beans (Phaseolus vulgaris L. “Kintoki”), 10g sucrose, 10g agar-powder and water to make 1 liter. However, an addition of the bean meal extracts to potatodextrose agar did not increase sporangial yield. It seems to indicate that the fungi needs no specific substance to promote sporulation.2. An addition of alanine to potato-dextrose agar containing 1 per cent sucrose caused little change in mycelial growth, but a great increase in sporulation. However, it caused no increase in sporulation of the fungus on bean-meal agar.3. Among the constituents of the medium, the balance of nitrogen and sugar is the most important in sporulation of P. infestans. The favorable ratio of the carbon-nitrogen elements of the semisythetic medium in sporulation is about 7.7. In the present experiment, the optimum concentration of carbon and nitrogen sources in the basal medium appears to be at about 1 per cent sucrose and 0.2 per cent L-arginine monohydrochloride.