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Abstract: Armillaria root rot, caused by Armillaria tabescens and Armillaria mellea, is a major cause of premature tree death in peach orchards in the southeastern United States. The root systems of infected trees can become entirely colonized by Armillaria, serving as an inoculum source for adjacent trees and providing massive inoculum levels in replant situations. If dead or dying trees could be colonized by an effective competitor of Armillaria before their removal, the extent of root colonization by the pathogen could be reduced, thus decreasing the threat to adjacent trees and/or subsequent plantings. Interactions between five species of saprobic lignicolous fungi (Ganoderma lucidum, Hypholoma fasciculare, Phanerochaete velutina, Schizophyllum commune, and Xylaria hypoxylon) and the two Armillaria species were examined in controlled conditions to provide proof of concept for competitive exclusion of Armillaria from peach roots. On agar-coated glass slides, all five potential antagonists induced detrimental reactions in >58% of the Armillaria hyphae observed, with the majority resulting in hyphal swelling or granulation. On poplar wood blocks, all antagonists consistently either overgrew Armillaria colonies or—in the case of S. commune—engaged in deadlock reactions; in all cases, the viability of Armillaria colonies was reduced to <30% of that of unchallenged controls. When inoculated simultaneously onto opposite ends of peach root segments, all antagonists consistently reduced growth and viability of Armillaria on and under the bark, whereby reduction of pathogen growth underneath the bark, Armillaria’s primary ecological niche, was most pronounced for G. lucidum, S. commune, and X. hypoxylon. When root segments were allowed to be colonized entirely by Armillaria before being inoculated with the antagonists, the latter were able to overgrow the pathogen on the root surface but unable to pre-empt it from underneath the bark. In summary,G. lucidum, S. commune, and X. hypoxylon caused strong hyphal and mycelial interference reactions and the most pronounced reductions in growth of Armillaria above and below the bark, indicating that they would be the most promising candidates for field-scale evaluations to restrict colonization of dead or dying peach trees by Armillaria in the orchard. [Copyright &y& Elsevier]

Summary Armillaria root disease (ARD) occurrence on ponderosa pine (Pinus ponderosa ) is not uniform in the Black Hills of South Dakota, USA. To help manage this ecosystem, a model was developed to predict the probability of observing diseased trees. A kernel density estimator was used to estimate the probability of observing ARD using presence data from two field studies. An eight-parameter regression equation using topographical data (Universal Trans Mercator coordinates, elevation and slope) derived from a Digital Elevation Model was fitted to the estimated probabilities and the residuals kriged to produce correction factors for the regression estimates. The final model, which had a relative mean squared error of 0.128, identified two peaks of high probability in the north-west portion of the Black Hills and several peaks of moderate probability throughout the Black Hills. [ABSTRACT FROM AUTHOR]