In the southeastern United States, the practice of replanting of peach trees on the same orchard site and expansion of production into cleared forest lands have resulted in an increased prevalence of Armillaria root and crown rot, which develops in these situations due to contact between the roots of newly planted trees and infected residual root pieces in the soil. The limited success in managing Armillaria root disease is in part due to a lack of knowledge regarding the biology of fungi in the genus Armillaria in orchard ecosystems. A series of three studies was carried out to clarify selected aspects related to establishment, spread, and persistence of Armillaria in peach orchards. Specifically, these studies provided basic information on the biochemical characterization of Armillaria species, the extent of potential inoculum in the form of residual root pieces in orchard replant situations, and the potential for restricting colonization and persistence of Armillaria on peach roots with saprophytic antagonists. Using fatty acid methyl ester (FAME) analysis, it was determined that thallus type (mycelium, sclerotial crust, or rhizomorphs) did not affect overall cellular fatty acid composition of Armillaria, and that FAME profiles could be used to identify Armillaria isolates to species. Ground-penetrating radar was used to detect residual peach roots in the field, quantify residual root mass following orchard clearing, and document that residual root fragments are of a size favoring Armillaria survival and infection. In an investigation of interactions between several species of saprophytic lignicolous fungi and Armillaria, such fungi induced hyphal and mycelial interference reactions against Armillaria and reduced growth of the pathogen when paired with it on peach roots, indicating the potential for restricting Armillaria colonization of dead or dying root tissue in the field. Knowledge gained from these studies contributes to a better understanding of and the potential for improved management of Armillaria root rot on peach and other stone fruits in the southeastern United States.
