Interaction between the soil yeast Rhodotorula mucilaginosa and the arbuscular mycorrhizal fungi Glomus mosseae and Gigaspora rosea

The effect of the soil yeast, Rhodotorula mucilaginosa LBA, on Glomus mosseae (BEG n°12) and Gigaspora rosea (BEG n°9) was studied in vitro and in greenhouse trials. Hyphal length of G. mosseae and G. rosea spores increased significantly in the presence of R. mucilaginosa. Exudates from R. mucilaginosa stimulated hyphal growth of G. mosseae and G. rosea spores. Increase in hyphal length of G. mosseae coincided with an increase in R. mucilaginosa exudates. No stimulation of G. rosea hyphal growth was detected when 0.3 and 0.5 ml per petri dish of yeast exudates was applied. Percentage root length colonization by G. mosseae in soybean (Glycine max L. Merill) and by G. rosea in red clover (Trifolium pratense L. cv. Huia) was increased only when the soil yeast was inoculated before G. mosseae or G. rosea was introduced. Beneficial effects of R. mucilaginosa on arbuscular mycorrhizal (AM) colonization were found when the soil yeast was inoculated either as a thin agar slice or as a volume of 5 and 10 ml of an aqueous solution. R. mucilaginosa exudates (20 ml per pots) applied to soil increased significantly the percentage of AM colonization of soybean and red clover.