Evaluating the Pathogenicity of Pythium vexans Isolates from Fraser Fir in North Carolina

Abstract

The pathogenicity of Pythium vexans isolates collected from fir samples with typical root rot symptoms in North Carolina was evaluated on Fraser fir seedlings (Abies fraseri). Two replicated pathogenicity trials involving seven treatments were conducted in the lath house and greenhouse. Although the P. vexans isolates examined in these trials were able to colonize Fraser fir root systems, they did not cause mortality or incite root rot symptoms. In comparison, Phytophthora cinnamomi, a known aggressive pathogen of Fraser fir, caused severe root rot symptoms in all plants. These experiments provided no evidence that P. vexans is a pathogen of Fraser fir.Accepted for publication 12 July 2008. Published 6 October 2008.Christmas trees are important nursery crops in the USA, with North Carolina leading production of Fraser fir, but phytophthora root rot and stem canker have casued significant damage. Recently, samples of Fraser and Canaan fir with typical root rot symptoms were diagnosed with Pythium vexans. Some experts were unsure how to respond. This research evaluated the pathogenicity of P. vexans on Fraser fir. Phytophthora cinnamomi, known as an aggressive pathogen on this host, was used as a standard for comparison.