Oospore Production Research Articles

Oospore production in paired cultures of Phytophthora species

Using a slide-culture technique examination of four strains of Phytophthora cinnamomi and five of P. cryptogea, growing in pairs, has shown that hybridization takes place, P. cinnamomi forming the antheridium and P. cryptogea the oogonium. Later, some of the cinnamomi isolates form non-hybrid oospores, apparently stimulated by conditions in the dual culture. A sixth cryptogea strain produces oospores when grown with members of either species.

PHYTOPHTHORA ERYTHROSEPTICA PETHYBR. IN RELATION TO ITS ENVIRONMENT

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.

Biological specialization in phytophthora infestans

Phytophthora infestans as it occurs in most parts of North America either is not biologically specialized or else the varieties of potatoes and tomatoes now grown are not kinds that reveal the presence of more than one form. The form prevalent in North America is the same as the one which occurred at Moscow in 1928 and at Munich in 1930. The demonstration of a biotype in Pomerania in 1932 may be attributed to a new form arising from the production of viable oospores of the fungus or to the fact that a hybrid possessingdemissum “blood” serves to bring out the existence of such a type.