EFFECT OF SOME PLANT FLAVONOIDS ON INVITRO BEHAVIOR OF AN ARBUSCULAR MYCORRHIZAL FUNGUS

The effect of 2 isoflavonoids (the soybean phytoalexin, glyceollin I, and the coumestan, coumestrol) and 1 flavonoid, quercetin, were tested on in vitro spore germination of Gigaspora margarita. Glyceollin I and coumestrol were tested at 0, 0.05, 0.5, 5 and 50 muM in water agar containing 0.5% ethanol. Quercetin was tested at 0, 0.1, 1 and 10 muM in pure water agar. All germination parameters were measured after 5 and 7 d. Germination rate was not significantly affected by any of these compounds. The number of germ tubes per spore was slightly increased by glyceollin I; mycelium length from germinated spores was increased by low concentrations of glyceollin I but was significantly decreased at the highest concentration. A positive correlation was found between coumestrol concentration and mycelium length, and vesicle number was decreased by coumestrol, quercetin and the highest concentration of glyceollin but was increased by glyceollin at 0.5 muM. Results are discussed in relation to the potential of flavonoids and isoflavonoids in acting as regulatory factors in plant-AM fungus interactions.