VIEW ARTICLE

Ecology and Epidemiology

Overwintering and Survival of Phytophthora cinnamomi in Fraser Fir and Cover Cropped Nursery Beds in North Carolina. C. M. Kenerley, Former graduate research assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27650, Present address of senior author: Department of Plant Sciences, Texas A&M University, College Station 77843; R. I. Bruck, professor, Departments of Plant Pathology and Forestry, North Carolina State University, Raleigh 27650. Phytopathology 73:1643-1647. Accepted for publication 22 June 1983. Copyright 1983 American Phytopathological Society. DOI: 10.1094/Phyto-73-1643.

Phytophthora cinnamomi survived extended periods of soil temperatures at or below 0 C for two consecutive winters as chlamydospores free in the soil, in pieces of organic matter, or in roots of symptomatic and asymptomatic Fraser fir (Abies fraseri) seedlings. Inoculum densities decreased markedly in December and January as soil temperatures fell below 0 C. Decreasing inoculum densities were found to be highly correlated (P = 0.01) with decreasing soil temperatures. Soil matric potential (when >- 0.45 bars), soil texture, initial inoculum density, or seedling age were not correlated with decreasing inoculum densities. Propagules of P. cinnamomi were recovered at every sampling date (October to June) from nonrhizosphere soil in plots with Fraser fir, crimson clover, rye, or left fallow and from rhizosphere soil of crimson clover and rye plants. Chlamydospores were the most frequent form of P. cinnamomi isolated from the soil or root tissue during the winter and spring months. Survival of P. cinnamomi in the roots of asymptomatic seedlings demonstrated that foliar symptom expression is not a reliable indicator of the incidence of infection within a nursery bed.