Acaulospora spinosissima, a new arbuscular mycorrhizal fungus from the Southern Guinea savanna in Benin

A new arbuscular mycorrhizal fungus was isolated from the Southern Guinea savanna in Benin, which represents a tree-rich savanna in the transition between the tropical atlantic rainforests and grass-rich savannas in sub-Saharan West Africa. The fungus was propagated in bait cultures and monosporic single species cultures, and is here described as Acaulospora spinosissima. It forms spores similar to those of Acaulospora spinosa, but in A. spinosissima the outer wall is thinner and the surface ornamentation is finer. Sequences obtained from the ITS and the partial 28S of the ribosomal gene revealed that the two species are phylogenetically not closely related. The new fungus was recovered from natural savanna at two locations and from one field site under yam cultivation in the first year after tree clearance. It was not detected in agricultural field sites cultivated for more than one year.