Induction of localized and systemic protection against Phytophthora parasitica var. nicotianae by tobacco mosaic virus infection of tobacco hypersensitive to the virus

Abstract

Within 3 days of inoculating expanded leaves of Nicotiana tabacum cv. Windsor Shade 117 with tobacco mosaic virus (TMV), viral lesions were apparent and, in younger uninoculated leaves, systemic induced protection was detected against race 3 of Phytophthora parasitica var. nicotianae. This protection occurred on all leaves above the TMV-inoculated leaves for at least 22 more days. The level of protection usually approached absolute (less than one fungal lesion per leaf as compared to 3 to 14 fungal lesions per leaf on unprotected plants). As few as 12 TMV local lesions per inoculated leaf were sufficient to induce significant levels of systemic protection. Localized protection was also induced within 3 days of inoculating leaves with TMV, but 7 days were required to induce significant levels of protection in half-leaves opposite TMV-inoculated half-leaves. TMV-inoculated plants flooded with a zoospore suspension or transplanted to infested soil developed fewer black shank infections and were less extensively damaged than control plants.