Detection of Phytophthora cinnamomi in Forest Soils by PCR on DNA Extracted from Leaf Disc Baits

Abstract

Phytophthora cinnamomi Rands causes root rot in a number of important forest tree species around the world, including American chestnut (Castanea dentata) and shortleaf pine (Pinus echinata). Conventional methods for detecting P. cinnamomi in forest soils may require too much time and space to permit widescale and long-term screening of the large sample numbers required for landscape-scale distribution analysis. This project compared conventional detection methods (baiting with full rhododendron leaves or leaf discs and subsequent culturing on selective media) with a molecular detection method using DNA extracted from leaf baits. These methods were comparable, and the DNA-based method was correlated with culture-based methods. In a field-validation screening using the leaf bait polymerase chain reaction method, P. cinnamomi was found across a range of topographic conditions, including dry ridge-top sites and moist lowland sites. Soil texture analysis supports the traditional association of P. cinnamomi with finer-textured soils. Further large-scale surveys are necessary to elucidate landscape-scale distribution patterns in eastern U.S. forests.