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Tomohiro Okada and Yoh-ichi Matsubara

Tolerance to fusarium root rot and the changes in free amino acid contents in mycorrhizal asparagus (Asparagus officinalis L., cv. Welcome) plants were investigated. Sixteen weeks after inoculation of arbuscular mycorrhizal fungus (AMF; Glomus sp. R10), mycorrhizal plants showed higher dry weight of ferns and roots than non-mycorrhizal plants, and AMF colonization level in a root system reached up to 73.3%. Ten weeks after Fusarium oxysporum f. sp. asparagi (Foa; MAFF305556, SUF1226) inoculation, disease incidence and the severity of symptoms were eased and disease indices were low as less than 20 in mycorrhizal plants compared with non-AMF plants in the both isolates. As for the changes in free amino acid, total free amino acid contents in ferns and roots were higher in AMF plants than non-AMF plants 16 weeks after AMF inoculation. In this case, eight constituents of amino acids in ferns and 16 in roots increased in AMF plants; in particular, arginine and gamma-aminobutyric acid (GABA) showed considerable increase in both ferns and roots in AMF plants. In the Foa culture by Czapec-Dox medium in vitro, suppression of Foa propagation was recognized by the addition (0.1, 1%, w/v) of arginine and GABA. From these findings, plant growth enhancement and tolerance to fusarium root rot occurred in mycorrhizal asparagus plants, and the disease tolerance was supposed to be associated with the symbiosis-specific increase in free amino acids.