The ARR Problem

Infected peach roots with characteristic cream colored mycelia.The causal soil fungi of Armillaria Root Rot (ARR) represent several Armillaria species that are geographically isolated across the nation, including A. mellea in California, Desarmillaria tabescens in the southeastern U.S. and A. ostoyae in Michigan. As a facultative necrotroph, these fungi colonize and kill the root system, effectively killing the tree prior to its maximum productivity. ARR disease is easy to recognize and diagnose when the bark of infected trunks or roots is peeled back as the characteristic cream-colored fungal mycelia is visible.

The first above ground symptoms are typical of water stress as the pathogen mycelium reduces the flow of water and nutrients to the plant. Infected trees will then collapse, but the effects are long-lasting. Orchard land is rendered unsuitable for further peach or cherry production as the inoculum (vegetative fungal mycelium) can survive in the soil on infected root pieces for years to come. Current ARR management practices such as chemical applications are unable to eradicate the pathogen and have a temporary effect. Thus, longer-term solutions are required to overcome the ARR threat.

The four main project goals to address the ARR problem and promote sustainable peach and cherry crop production were accomplished under the Multistate Specialty Crop Block Grant from the United States Department of Agriculture (USDA) Agriculture Marketing Service Specialty Crop Multistate Project, “Short and long-term solutions for Armillaria root rot in Prunus” (USDA-AMS-SCMP-2015-10.170).

Objective 1. Evaluate and mechanize Above-Ground Root Collar Excavation as a strategy to mitigate losses in peach due to Armillaria infection.

Objective 2. Improve the efficiency of hybrid Prunus rootstock propagation to allow cost-effective tree production by commercial nurseries.

Objective 3. Identify antifungal compounds with activity against Armillaria spp. that are naturally produced in Prunus (phytoanticipins).

Objective 4. Accelerate the breeding of Armillaria resistant rootstocks for peach and cherry through the use of DNA information.