Armillaria root rot on highbush blueberry in northern Italy: monitoring, identification and inoculum sources

Highbush blueberry plants infected by Armillaria spp. were reported in north-eastern Italy (Province of Trento). After inspection, 13 blueberry orchards were found to be infected in the Valsugana valley. Armillaria sp. samples were collected from blueberry plants, from bark spread on the blueberry rows and from infected trees and stumps in the orchard surroundings. The species determination was performed using a species-specific multiplex PCR approach. Efficacy trials with potential biocontrol agents against Armillaria sp. were carried out on young blueberry plants. The average percentage of stunted plants in the infected fields was 11%, while the percentage of dead plants was generally very low (average of 1.5%). The most frequent species infecting blueberries were A. gallica and A. mellea: in each field one species largely dominated the other. The tested Trichoderma strains, especially T. atroviride SC1, were the most effective biocontrol agents against A. gallica and A. mellea.