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Protection of Tobacco Against Phytophthora parasitica var. nicotianae by Cultivar-Nonpathogenic Races, Cell-Free Sonicates, and Pratylenchus penetrans. John L. Mc Intyre, Assistant Plant Pathologist, The Connecticut Agricultural Experiment Station, New Haven, CT 06504; P. M. Miller, Plant Pathologist, The Connecticut Agricultural Experiment Station, New Haven, CT 06504. Phytopathology 68:235-239. Accepted for publication 25 July 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-235.

Tobacco cultivars L8 and 1071 were protected against cultivar-pathogenic races of Phytophthora parasitica var. nicotianae by cultivar-nonpathogenic races. Protection was localized within 1 cm of the site of injection. Sonicates of all races protected these cultivars and the susceptible cultivar Windsor Shade 117 (WS 117). Protection occurred only when tobacco cultivars were exposed first to the sonicate and then were challenged. Protection occurred within 12 hr of sonicate application, reached a maximum by 24 hr, and thereafter decreased through 96 hr. Sonicates did not inhibit germination of zoospores of the pathogen in vitro. Infection by the lesion nematode, Pratylenchus penetrans, also protected WS 117 against P. parasitica var. nicotianae. This protection was similar to the above except that it was longer-lived, presumably due to the continual irritation of the plant by the nematode. The results indicate that the protective response is nonspecific and that a host response is required for protection to occur.

Additional keywords: induced resistance, Nicotiana tabacum, black shank.