Water availability and formation of propagules of arbuscular mycorrhizal fungi associated with sorghum

• Water availability has no effect on the number of nuclei of AMF.
• The number of glomerospores is not directly related to the inoculum infectivity.
• AMF have distinct sporulation strategies under different levels of water availability.

Arbuscular mycorrhizal fungi (AMF) promote greater tolerance to the negative effects of water stress in their host plants, yet may also be influenced by the availability of water in the production of their infective propagules. The objective of this study was to assess the effect of water availability in the soil on the sporulation of Claroideoglomus etunicatum, Gigaspora albida and Scutellospora heterogama, and the influence of this condition on the infective potential and number of nuclei in glomerospores of these species. The reduction of water availability from 75 to 25% did not decrease significantly the sporulation of C. etunicatum, but resulted in decrease of sporulation of G. albida (600 to 7 glomerospores per 30 g−1 soil) and S. heterogama (274 to 2 glomerospores per 30 g−1 soil). The water availability at 75 and 71% promoted maximum sporulation of G. albida and S. heterogama, respectively. While G. albida and S. heterogama had greater sporulation than C. etunicatum, the infective potential of these species was lower, which may be related to the life-strategy and type of infective propagules of each species. The number of nuclei per glomerospore varied only among the species (p < 0.05), with C. etunicatum and G. albida presenting the higher number of nuclei when compared to S. heterogama, but no differences were found among the treatments of water availability (p > 0.05). These results suggest that AMF have distinct sporulation strategies and the amount of glomerospores is not directly related to the infectivity of the inoculum. Possibly, the differences in the life-strategies among the species were greater than the effects of water availability.