Studies On Spore Germination And Presymbiotic Growth Of AM Fungi

Arbuscular mycorrhiza (AM) fungi form mutualistic, symbiotic associations with the roots of more than 80% of land plants, which facilitate plant mineral nutrient uptake, enhance tolerance of environmental stress and plant diseases. The fungi contribute to maintenance of plant diversity and ecosystem.Because of obligate biotroph, AM fungi are incapable of completing their life cycle in the absence of a host root. Spore germination and hyphal growth are important events in symbiotic development stage of AM fungi which determine colonization of AM fungi and establishment of arbuscular mycorrhiza.The aim of the present work is to evaluate effect of cold treatment, different substrates, heavy metal and flavonoids on spore germination, hyphal growth of AM fungi, Gigaspora margarita, Glomus mosseae, Glomus clarerdium and Glomus geosporum. The main results were as follows:Storage of spores at 4℃～6℃for more than six months can signifcantly enhanced the spore germination percentage; The best results came from 12 months' treatment, in which the spore germination percentage of Gi. margarita, Gl. mosseae and Gl. clarerdium was 93.5%, 73.5% and 76%, respectively. While long time storage reduced spore germination.The water-agar medium was the most feasible for spore germination at the 7th day, followed by the MS medium at the 14th day. Conversely, the sand and the soil medium did not allow high germination. Spores maintained in water-agar also presented longer germ tubes than spores in the other treatments.Heavy metal, Zn²⁺ and Cu²⁺ inhibited the germination percentage and hyphal growth at high concentration. The spores germination and hyphal growth for both isolates showed a variable responses to different concentrations of Zn²⁺ and Cu²⁺, Zn²⁺ at low concentrations increased germination percentage and hyphal growth for both isolates spores compared to control (without metal).Flavonoid compounds, quercetin and rutin stimulated spore germination and hyphal development of Gi. margarita, and quercetin, ranging between 0.5μmol L-1 and 8μmol L-1, significantly promoted hyphal growth, hyphal branching and formation of clusters of auxiliary cells, increasing hyphal length, number of hyphal branches and clusters of auxiliary cells by two or three times as compared with the control group, while the other types of flavonoids showed little effect on pre-symbiotic growth of Gi. margarita. Appropriate in concentration, formononetin, genistein and naringin, had positive effect on spore germination, hyphal growth and hyphal branching of Gl. geosporum, and apigenin, flavanon and naringin did formation of secondary spores. Biochanin A merely had some stimulating effect on spore germination of Gl. Geosporum. Variation of the effect of Flavonoids on development of arbuscular mycorrhizal spores depends on type and concentration of flavonoid compounds involved, and different flavonoids play different roles in promoting spore germination, hyphal growth and hyphal branching and formation of secondary spores at pre-symbiotic growth stage of the AM fungi.