(311) Armillaria Root Rot of Peach: A Multipronged Approach

Abstract

Armillaria root rot (ARR) of peach caused by the soil-borne basidiomycete fungus Armillaria tabescens is causing premature decline and mortality of peach trees on most southeastern U.S. peach farms. Soil inoculum may be present both in former peach orchard sites and on sites that were once in hardwood forest. The fungus is protected under the bark of dead root pieces and may survive up to 100 years at various depths in the soil profile. No commercially available rootstocks are resistant to ARR. Since 2002, we have embarked on a multipronged strategy to develop control options to combat ARR. First, we have two replicated trials on commercial grower replant sites with a history of ARR. Trial 1 compares four preplant fumigation treatments (none, Telone II, methyl bromide, and Enzone), three rootstocks (Lovell, Halford, and Guardian) and preplant root dips with endomycorrhizal fungi. Trial 2 compares the use of raised beds, root collar excavation and preplant root dips. Both trials examine long-term productivity and tree survival. Second, we are examining the use of systemic fungicide injection into infected trees to protect trees around infection foci. Third, we are trying to develop a genetically modified ARR-resistant rootstock. We have inserted the gene encoding the gastrodia antifungal protein (GAFP—a low molecular weight lectin that binds mannose and chitin) from a Chinese orchid into tobacco (model herbaceous system) and plum (model Prunus system). GAFP has antifungal activity against several basidiomycete root rot pathogens. Pathogenicity tests with transformed tobacco plants show enhanced tolerance to several root rot pathogens when compared to nontransformed plants. Transformed plums are being multiplied for pathogenicity tests.