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Funded Project

Funding Program: Regional IPM Grants (S-RIPM)

Project Title: Development and Evaluation of Integrated Disease Management Tactics for Amillaria Root Rot of Peach

Project Director (PD): Harald Scherm [1]

Lead State: GA Lead Organization: University of Georgia

Research Funding: $99,245

Start Date: Aug-01-2003 End Date: Jul-31-2005

Summary: None provided Objectives: None provided

Final Report:

Results From report submitted by the PI to USDA CRIS report system. PROGRESS: 2003/08 TO 2005/12 Objective 1: Several previously published primer sets utilizing rDNA variation were evaluated in an attempt to identify and characterize southeastern Armillaria isolates: IGS primers Ata1/Ata2 and Ame1/Ame2 (Sicoli et al.); ITS primers AtITS1, AmITS1, and ITS2 (Schnabel et al.); and universal IGS primers LR12R/O-1 followed by restriction analysis with Alu1 (Harrington & Wingfield). Results of these analyses have been conflicting, with one method indicating all isolates to be A. tabescens and the others suggesting presence of complex genotypes in addition to A. tabescens-A. mellea hybrids. Fatty acid analyses of isolates provided more consistent results, with virtually all isolates identified as A. tabescens. Fatty acid profiles were not affected by differences in thallus morphology (hyphae vs. mycelial sheets or rhizomorph initials), and Armillaria species could be differentiated from each other based on 14:0, 18:1w11c, and 24:0-iso fatty acids and from other white-rotting basidiomycetes using 16:0, 16:1w5c, and 23:0 fatty acids. - Objective 2: A long-term field trial to evaluate the effects of rootstocks (Nemaguard and SL0040), fumigants (MeBr, MeI, and 1,3-D + C35), and the biocontrol agent Trichoderma harzianum T-22 on peach tree longevity was established on an Armillaria-infested site at the USDA-ARS research station in Byron, GA, in spring of 2003. Since then, the site has been maintained using horticultural practices similar to those used commercially. In May of 2004, T. harzianum was reapplied to the biocontrol plots as a soil drench at a rate of 5 oz/100 gal with 20 gal of the suspension applied per seven-tree plot. Tree losses to date have been minimal and unrelated to Armillaria root rot. We expect Armillaria-related mortality in this long-term trial to commence shortly and increase gradually over the next 3 to 5 years in the check treatments. - Objective 3: In laboratory microcosm experiments, species of Ganoderma, Schizophyllum, and Xylaria showed the most promise for pre-empting Armillaria on artificially inoculated peach root segments. Therefore it was decided to include representatives of these species in the field trial, in addition to the cord-former Hypholoma fasciculare mentioned in the proposal. A declining peach planting at the USDA-ARS research station in Byron, GA, was selected for application of the stump herbicide and saprophytic competitors of Armillaria. Pathway herbicide (picloram + 2,4-D) was applied to fresh cuts made in the lower trunk area of each tree in April of 2004; the treatment was reapplied to surviving trees in September. In November, trees were inoculated with either Ganoderma lucidum, Xylaria hypoxylon, or Hypholoma fasciculare. These fungi had been grown on poplar dowel rods, and two colonized dowel rods were inserted into predrilled holes on the sides of the trunk above the soil level. Control treatments consisted of uncolonized dowel rods. In spring of 2006, trees will be cut and the root systems excavated and assessed for colonization by the saprophytes and/or Armillaria. IMPACT: 2003/08 TO 2005/12 The key impacts of this project have been as follows: 1) Characterized the genetic diversity of Armillaria species and strains from peach in the southeastern United States using DNA and fatty acid-based methods. 2) Developed a fatty acid-based method for identifying Armillaria species and for distinguishing Armillaria from other lignicolous basidiomycetes. 3) Developed a method to detect and quantify residual root pieces, the main source of Armillaria inoculum in replant situations, in peach orchards. 4) Established ongoing long-term field trials to evaluate selected pre-, at-, and post-plant management tactics, alone or in combination, against Armillaria root rot in peach orchards. PUBLICATIONS (not previously reported): 2003/08 TO 2005/12 1. Beckman, T.G., and Lang, G.A. 2003. Rootstock breeding for stone fruits. Acta Horticulturae 622:531-551. 2. Cox, K. 2004. Armillaria Root Rot of Peach: Biochemical Characterization, Detection of Residual Inoculum, and Interspecies Competition. Ph.D. dissertation, Department of Plant Pathology, University of Georgia, Athens. 3. Cox, K.D., and Scherm, H. 2006. Interaction dynamics between saprobic lignicolous fungi and Armillaria in controlled environments: Exploring the potential for competitive exclusion of Armillaria on peach. Biological Control (in press, doi:10.1016/j.biocontrol.2006.01.012). 4. Cox, K.D., Scherm, H., and Beckman, T.G. 2004. Armillaria root and crown rot. Pages 162-166 in: Southeastern Peach Grower's Handbook (D. Horton and D. Johnson, eds.). University of Georgia, College of Agricultural and Environmental Sciences, Athens. 5. Cox, K.D., Scherm, H., and Riley. M.B. 2006. Characterization of Armillaria spp. from peach orchards in the southeastern United States using fatty acid methyl ester profiling. Mycological Research (in press). 6. Cox, K.D., Scherm, H., and Serman, N. 2005. Ground-penetrating radar to detect and quantify residual root fragments following peach orchard clearing. HortTechnology 15:600-607. 7. Kelly, K.L. 2004. Molecular Characterization of Southeastern Armillaria Isolates. M.S. thesis, Department of Horticulture, University of Georgia, Athens.

Outcomes N/A

Impacts The key impacts of this project have been as follows: 1) Characterized the genetic diversity of Armillaria species and strains from peach in the southeastern United States using DNA and fatty acid-based methods. 2) Developed a fatty acid-based method for identifying Armillaria species and for distinguishing Armillaria from other lignicolous basidiomycetes. 3) Developed a method to detect and quantify residual root pieces, the main source of Armillaria inoculum in replant situations, in peach orchards. 4) Established ongoing long-term field trials to evaluate selected pre-, at-, and post-plant management tactics, alone or in combination, against Armillaria root rot in peach orchards.

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