Effect of arbuscular mycorrhizas on crown rot (Phytophthora cactorum) in micropropagated strawberry plants

Preliminary studies were conducted on the effect of arbuscular mycorrhizal fungi (AMF) against strawberry crown rot caused by Phytophthora cactorum (Leb. & Cohn) Schroet. A micropropagated strawberry cultivar susceptible to the disease, ‘Jonsok’, was either inoculated with the Finnish AMF strains Glomus mosseae (Nicol. & Gerd.) Gerdemann & Trappe V57, G. hoi Berch & Trappe V98 and G. fistulosum Skou & Jakobson V128, or it was left uninoculated. AMF inoculation at the beginning of the weaning stage, five weeks before the establishment of the pot or field experiment, did not decrease crown rot severity in either of the experiments. In the pot experiment, on the contrary, AMF lowered the plant health index when P. cactorum was added to the substrate in the form of infected plant residues. Results are discussed in relation to soil-borne vs. foliar disease, phosphorus concentration of the growth substrate and influence of weather conditions