The high availability of metallic ions in the soil, including Mn2+, may inhibit arbuscular mycorrhizal fungi (AMF), slowing down spore germination and, consequently, the mycorrhiza formation, therefore decreasing the symbiotic effectiveness. The aim of this study was to evaluate the effect of Mn2+ ions on spore germination in six AMF species of the genera Glomus, Acaulospora, Gigaspora and Scutellospora under in vitro conditions. Different Mn2+ doses (15, 30 and 75 mg kg-1) as MnCl2.4H2O were added to a washed sand substrate, keeping a control without Mn addition. Spores were accommodated in membranous envelopes which were placed between two sand layers treated with the above Mn doses in Petri dishes. After a 30 day incubation period, spore germination was evaluated, presenting decreases (32, 49 and 75 %) as Mn doses increased, compared to the control. Spore germination in the genus Glomus was completely inhibited at the top dose, while in the Acaulospora genus it dropped down to 50 % even at the lowest dose (15 mg kg-1 of Mn2+). The genera Scutellospora and Gigaspora presented highest germination indexes, out of which Gigaspora presented Mn tolerance, even at the highest Mn2+ dose. Scutellospora presented stimulus for germination up to doses of 30 mg kg-1 of Mn2+.
fungistasis; heavy metal; Glomales