Abstract
Treatment of the lower three leaves of potato plants with hyphal wall components of Phytophthora infestans systemically activated in upper leaves an O-2 generating reaction from 1 to at least 7 days after treatment. In the same leaves activation of superoxide dismutase immediately followed the enhanced O-2 generating reaction. Peroxidase activity increased linearly from 3 days after treatment. In the leaves activated for O-2 generation, superoxide dismutase and peroxidase, challenge inoculation with a zoospore suspension of P. infestans caused further enhancement of the O-2 generating reaction from 1 to 5hr after inoculation. The percentage of successful penetrations by the fungi and the appearance of susceptible lesions were greatly reduced in such tissues. The systemic activation of O-2 generating reaction is discussed in relation to induction of systemic resistance.
