Production of Pectic Enzymes by Phytophthora infestans

Abstract

PECTIC enzymes have been shown to be produced in vitro by many plant pathogenic fungi, and evidence has been presented which suggests that they may play a part in the mechanisms of infection of the host plant¹. Most work has been concerned with relatively non-specialized facultative parasites. Little is known about obligate parasites, for which the only record is of polygalacturonase production by germinating uredospores of Puccinia graminis tritici², and the difficulty of obtaining uredospore suspensions in axenic culture makes this work somewhat suspect. Phytophthora infestans shares certain features in common with obligate parasites, showing a high degree of host specificity³, has much more exacting nutritional requirements in vitro than most facultative parasites^4,5, and forms haustoria⁶. The processes of germination in vitro appear similar to that of many obligate parasites, as zoospores readily germinate on a wide range of natural and synthetic media but do not readily continue growth to form actively growing colonies⁷. Thus the following observations on the ability of Phytophthora infestans to produce pectic enzymes may be of some interest.