Tolerance of asparagus seedlings infected with arbuscular mycorrhizal fungus to violet root rot caused by Helicobasidium mompa

Tolerance of seedlings of asparagus (Asparagus officinalis L., cv. Mary Washington 500W) inoculated with four arbuscular mycorrhizal (AM) fungi [Gigaspora margarita (GM), Glomus fasciculatum (gf), Glomus mosseae (gm) and Glomus sp. R10 (gr)] to violet root rot caused by Helicobasidium mompa Tanaka was investigated. Twelve weeks after AM fungal inoculation, the infected asparagus seedlings grew better than did the noninoculated ones; the effect was more pronounced with GM and gr than with gf and gm. AM fungal infection level in the root system was highest with gr and lowest with gm. Symptoms of violet root rot appeared in all the treatments 12 weeks after H. mompa inoculation, but the severity of the incidence was less in AM fungus-inoculated plants (9.1-45.5%) excluding gm-inoculated plants (63.6%) than AM fungus-noninoculated plants (54.5%). The disease indices revealed that the incidence was remarkably low, especially, in gr-inoculated plants. Moreover, healthy plants of AM fungus-inoculated plants grew more vigorously than did the noninoculated ones. These results reveal that plant growth promotion occurred in asparagus seedlings infected with the four AM fungal species and the tolerance to violet root rot appeared with most of the AM fungal species, though the effects differed with the AM fungal species.