Effect of ectomycorrhizal fungi on chestnut ink disease

Seedlings of Castanea sativa were inoculated at transplanting time with fou r ectomycorrhizal (ECM) fungi, Laccaria laccata, Hebeloma crustuliniforme, H. sinapizans and Paxillus involutus. At the end of the first vegetative se ason, 7 months after sowing, half of the mycorrhizal and nonmycorrhizal see dlings were challenged with a zoospore suspension of Phytophthora cambivora and the other half with P. cinnamomi. Five months later, mycorrhizal plant s infected with P. cambivora or P, cinnamomi showed no sign of pathogen inf ection. The ECM fungi increased plant biomass also in the presence of the p athogen. Mycorrhizal seedlings inoculated with the pathogens showed greater shoot and root development than nonmycorrhizal chestnut plants. All the fu ngi tested reduced the negative effect of the ink disease pathogens on the plant host in vivo. The mechanisms by which the ECM fungi protect chestnut seedlings are discussed.