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.
Tomohiro Okada and Yoh-ichi Matsubara
Abu Shamim Mohammad Nahiyan and Yoh-ichi Matsubara
Tolerance to fusarium root rot caused by Fusarium oxysporum f. sp. asparagi (Foa, MAFF305556 and N9-31) and the changes in antioxidative abilities in mycorrhizal asparagus (Asparagus officinalis L., cv. Welcome) plants were investigated. Asparagus plants were inoculated with arbuscular mycorrhizal fungus (AMF, Glomus sp. R10) and Foa was inoculated 10 weeks after AMF inoculation. AMF plants accumulated higher dry weight of ferns and roots than non-AMF plants before and after Foa inoculation. AMF colonization level reached more than 70% and no difference noted among the treatments. As for disease tolerance, non-AMF plants showed 100% in incidence of root rot and highest severity in both Foa isolates; the severity of symptom was relatively higher in MAFF305556 compared with N9-31. However, AMF plants showed lower severity than non-AMF plants in both Foa isolates. Before and after Foa inoculation, antioxidative abilities increased in most of the AMF plants than non-AMF in the following items: activity of superoxide dismutase (SOD) and ascorbate peroxidase (APX), 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, and total contents of polyphenol and ascorbic acids. These results suggest that plant growth enhancement and tolerance to fusarium root rot appeared in mycorrhizal asparagus plants. In this case, the disease tolerance might be associated with the increase in antioxidative ability.