Growth stimulatory substances and the axnic culture of vesicular-arbuscular mycorrhizal fungi

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By using the 25% MeOH eluates of Bahia grass roots, we first succeeded in the axnic culture of a vesicular-arbuscular mycorrhizal (VAM) fungus, Gigaspora ramisporophora (Ishii et al., 1995). This success of the culture will make a great contribution to not only extending the possibility of agricultural and industrial utilization of VAM fungi, but also developing the studies about the physiological and ecological properties of the fungi. In this study, we examined the isolation and identification of VAM-stimulatory substances from Bahia grass roots and the improvement of our axnic culture methods of VAM fungi. In addition, we investigated seasonal changes in VAM infection rate of Bahia grass roots. The results obtained are shown as follows :1) Three kinds of the growth stimulatory substances for VAM fungi were isolated from the 25% MeOH eluates of Bahia grass roots. One of them was identified as eupalitin (3.5-dihydroxy-6,7-dimethoxy-4'-hydroxy flavone). At 10 ppm, this compound significantly stimulated the in vitro hyphal growth of G.ramisporophora. The others were not indentified in this study.2) We developed an efficient medium for the culture of VAM fungi. When effects of some chemicals on hyphal growth of VAM fungi were examined in this medium, the growth was stimulated by alginate oligosaccharides, polyamines, eupalitin, and unpublished substances. In particular, the unpublished substances were quite effective on the germination of VAM spores.3) The percentage of VAM infection in Bahia grass roots was 50 and above for the period from mid june to early September. Particularly, the highest percentage was observed in early and mid August.