Pathogenicity of <em>Armillaria</em> Isolates Inoculated on Five <em>Quercus</em> Species at Different Watering Regimes

Abstract

One of three fungal isolates of Armillaria mellea (Vahl: Fr.) P. Kummer, A. gallica Marxm. et Romagn. and A. tabescens (Scop.: Fr.) Emel. was inoculated on 1,440 three-year-old potted seedlings of five Quercus species (Q. cerris L., Q. ilex L., Q. pubescens Willd., Q. robur L. and Q. trojana Webb.) grown at different watering regimes in a greenhouse. Inoculum was represented by a piece of an oak branch colonised with the fungus (or sterile, as a control), which was attached to the unwounded main root of each oak seedling. During the growing season, differences in water availability among seedlings were measured monthly using minimum water potential assessments on noninoculated seedlings receiving an equal amount of water. Although all three Armillaria isolates induced infection, the A. mellea isolate was most pathogenic in all cases, while the A. gallica isolate showed a statistically equal degree of pathogenicity only on the least watered seedlings. Of the Quercus species, Q. ilex showed the greatest number of infected seedlings, Q. robur the smallest. Reducing the water supply to potted oak seedlings could be a useful indicator for detecting differences in pathogenicity between Armillaria species.