PHYTOPHTHORA ERYTHROSEPTICA PETHYBR. IN RELATION TO ITS ENVIRONMENT

Abstract

Summary The present contribution, as part of a general study of pink rot of the potato, deals with Phytophthora erythroseptica Pethybr. in its relation to staling, light, acidity, moisture and temperature. In natural media the fungus is not, or but very slightly, affected by its own staling products, but, in general, is intensely intolerant to the presence of other fungi and bacteria. Ordinary daylight is not concerned in the growth or reproduction of the fungus. Growth occurs over a wide pH range (3·2 to circa 9·0–10·0); sexual reproduction occurs over this range except towards the limits of acidity and alkalinity; asexual reproduction was not investigated experimentally. It is considered that modification of the soil reaction, within practical limits, does not offer a means for control of the disease. The moisture factor controls directly the incidence of the disease in contaminated soil—with low moisture infection is inhibited; with normal moisture infection occurs via the dead or moribund stolon through the “heel” of the tuber; with high moisture the tuber is infected directly in the region of an “eye”. Sporangia are only formed under aquatic conditions and it is considered probable that “eye” infection is brought about through the agency of zoospores. The temperature limits of growth are 0–32°C. with an optimum at 25°C. Oospore production occurs only between the optimum and minimum growth temperatures (0–25°C), being inhibited above the growth optimum. Asexual reproduction seems to be similarly related to temperature.