Increased diversity of Phytophthora species in Fraser fir Christmas tree plantations in the Southern Appalachians

ABSTRACT

Phytophthora root rot (PRR) disease afflicts significant economic losses to the Fraser fir Christmas tree industry. In previous surveys conducted in 1972 and from 1997 to 1998 in North Carolina, the incidence of PRR was ∼9.5% with Phytophthora cinnamomi identified as the predominant causal species isolated from infected roots of Fraser fir. Due to increased use of out-of-state planting stock since 2000, we suspected increased diversity of Phytophthora species. During 2014, we surveyed Fraser fir Christmas tree plantations in the Southern Appalachians of North Carolina, Tennessee and Virginia to determine the occurrence of pathogenic root-rotting species of Phytophthora. A weighted sampling strategy based on Christmas tree acreage was deployed to collect symptomatic Fraser fir roots from 103 commercial production fields in 14 counties. Six species of Phytophthora were isolated from infected roots sampled from 82 sites in 13 counties. Phytophthora cinnamomi, P. cryptogea and P. pini represented 70.3%, 23.1% and 1.1% of the 91 isolates. Phytophthora citrophthora, P. europaea and P. sansomeana accounted for the remaining 5.5% of the isolates and have not been identified in previously published Fraser fir surveys conducted in the region. The pathogenicity of P. citrophthora on Fraser fir was confirmed based on completion of Koch’s postulates.

KEYWORDS:

• Abies fraseri
• North Carolina
• Phytophthora cinnamomi
• root rot
• survey

Acknowledgements

The authors are grateful to Avery Barr, Anne Margaret Braham and Kala Parker for their valuable technical assistance. We are thankful to Dr Gloria Abad at CPHST Beltsville Laboratory, Center of Plant Science and Technology at USDA-APHIS-PPQ, and we are also grateful to the numerous Christmas tree growers and Cooperative Extension personnel who graciously cooperated in this effort.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was supported by the Gunnar and Lillian Nicholson Graduate Fellowship and Faculty Exchange Fund, the USDA NIFA Specialty Crops Research Initiative (2012-51181-19940) and the North Carolina Agricultural Research Service via the Christmas Tree Genetics Program.