Root and Soil-borne Oomycetes (Heterokontophyta) and Fungi Associated with the Endangered Conifer, Torreya taxifolia Arn. (Taxaceae) in Georgia and Florida, USA

Abstract

A systematic survey was conducted to isolate and identify root and soil-borne oomycetes and fungi associated with the rare and endangered southeastern USA conifer, Torreya taxifolia Arn. Twenty four trees showing different degrees of decline were sampled at two different sites: Torreya State Park, Liberty County, Florida (n = 12) and US Corps of Engineers in Decatur, Georgia (n = 12). All T. taxifolia trees sampled showed moderate to severe levels of decline (100% decline incidence) based on criteria, such as poor development of trees, stunting and fragility. Disease severity was higher, and trees were smaller with poor development at Florida sites, showing an average height of 89 cm, and a diameter at breast height (DBH) of 5 cm compared to trees in Georgia's site (174 cm h and 10.6 cm DBH in average) In addition to decline, root necrosis and stem cankers were observed in 45.8 % of trees examined. A diverse fungal community was associated with declining trees. Twenty eight fungal genera were identified belonging to the Oomycetes, Zygomycetes, Ascomycetes, Basidiomycetes and anamorphic fungi. Anamorphic fungi, Oomycetes, and Zygomycetes were the dominant groups associated with T. taxifolia. Pestalotiopsis spp., Fusarium spp. and Pythium spp. were the most common genera. Most isolates were obtained from root tissue. Seventy four percent (74%) of isolates were from samples collected at a Georgia site. Alternaria spp., Cylindrocladium sp., Fusarium spp., Phoma sp., Pythium spp., Rhizoctonia sp., Thielaviopsis sp. and Verticillium sp. are among soil-borne oomycetes and fungal species identified. Not known Phytophthora spp. were isolated during the survey. Interactions of oomycetes and fungi inhabiting the soil and rhizosphere could play an important role in T. taxifolia's decline.