Poster: Diseases of Plants: Disease Detection & Diagnosis
Four species of Phytophthora recovered from roots of American and hybrid chestnut seedlings and associated soils in the southeastern US
S. SHARPE (1), S. Jeffers (1), S. Clark (2) (1) Clemson University, U.S.A.; (2) USDA Forest Service, U.S.A.
Since Phytophthora root rot (PRR) was first described on American chestnut in 1932, the only species of Phytophthora reported as a causal agent has been P. cinnamomi. In Europe, however, multiple species of Phytophthora are involved in PRR of native chestnut trees. In 2009, the USDA Forest Service began evaluating American, Chinese, and hybrid chestnut seedlings in forest test plots in NC, TN, and VA, but PRR caused some seedlings to die prematurely. The objective of this research was to determine if multiple species of Phytophthora may be causing PRR of American and hybrid chestnut seedlings. A total of 260 root and 454 soil samples were assayed from 2010 to 2014. Phytophthora spp. were recovered by isolation from roots on PARPH-V8 selective medium and baiting soil with rhododendron and camellia leaf pieces. All isolates were tentatively identified based on morphology; species identifications will be confirmed by DNA sequences. P. cinnamomi was recovered most frequently—from 41 (16%) root and 109 (24%) soil samples. However, P. cambivora and P. heveae were also recovered—from 18 (7%) and 2 (<1%) root samples and 18 (4%) and 17 (4%) soil samples, respectively. At a separate test site in SC, P. drechsleri was isolated from roots of several hybrid chestnut seedlings. This is the first report of Phytophthora species other than P. cinnamomi associated with PRR of pure and hybrid American chestnut. These species are being tested for pathogenicity to American chestnut.