VIEW ARTICLE

Ecology and Epidemiology

Effects of Soil Matric Potential on Infection of Tobacco by Phytophthora parasitica var. nicotianae. H. D. Shew, Assistant professor, Department of Plant Pathology, North Carolina State University, Raleigh 27650; Phytopathology 73:1160-1163. Accepted for publication 16 March 1983. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-1160.

Soil naturally infested with Phytophthora parasitica var. nicotianae was placed on Büchner funnel tension plates to control soil matric potential. A single 1-mo-old cultivar Hicks tobacco seedling was transplanted into each funnel and incubated for 21 days. With an initial inoculum density of 5,000 propagules per kilogram of soil, 60, 27, and 7% of the plants were infected at constant matric potentials of - 10, - 20, and - 50 millibars (mb), respectively. When plants were exposed to a single 24-hr saturation period after 1 wk of incubation at - 30 or - 50 mb, infection was significantly increased in comparison to plants not exposed to the saturation period. Initial inoculum densities of 40, 80, 170, 300, 700, 1,300, 2,700, and 5,300 propagules per kilogram of soil resulted in 73, 47, 80, 73, 80, 80, 100, and 93% infection, respectively, when plants were exposed to a 24-hr saturation period. Saturation periods as short as 0.5 hr overcame the inhibitory effect on infection of soil matric potentials of - 30 to - 50 mb. The mechanism of infection enhancement by soil saturation was apparently stimulation of zoospore release and dispersal.