Analysis of the symbiotic mechanism between vesicular-arbuscular mycorrhizal fungi and plants

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The results of our study are as follows :1) Some of the new growth stimulants for vesicular-arbuscular mycorrhizai (VAM) fungi in the 25 % methyl alcohol eluates of bahiagrass root extracts fractionated by flash chromatography were isolated and identified. One is 2, 3-dihydroxy eupalitin. The others are non-flavonoid compounds, and have a great stimulatory effect on hyphal growth.2) Application of root exudates to the soil stimulated VAM development of trifliate orange roots, and decreased tree growth inhibition by soil Al toxicity.3) In order to improve our axenic cultural techniques for VAM fungi, we investigated the effect of light on the growth of VAM fungi growth, while the wavelength around 450 nm (blue) inhibited it. By using the LEDs and new VAM growth stimulants, we tried further experiments.4) In order to clarify the mechanism of VAM symbiosis, we used some non-VAM plants such as Brassicaceae and Chenopodiaceae plants. The results indicated that the VAM symbiosis was related to the biosynthesis of ethylene.5) We discovered only one very highly colonized plant out of about 140 species of Arabidopsis plants in the Brassicaceae family. By using this plant, we are analyzing the genes related to VAM symbiosis.6) By using a high resolution CCD camera, we observed that the network by VAM hyphae was easily established when bahiagrass, millet and rat-tail fescue (Vulpia myuros) were intercropped in the soils planted trifoliate orange trees of papaya trees. However, there were a few hyphae in the soil intercropped with non-VAM plants, and very few hyphae in bare ground. The hyphal network establishment was mainly caused by the quantity and quality of grass root exudates. The results suggest that the introduction of sod culture using the grasses that help the propagation of VAM fungi will contribute to constructing a new fruit growing system with the lower input and sustained fruit productivity with environmental conservation in mind.