Glomus indicum, a new arbuscular mycorrhizal fungus

Abstract

A new arbuscular mycorrhizal fungal species of the genus Glomus , Glomus indicum (Glomeromycota), forming small, hyaline spores in hypogeous aggregates is described and illustrated. The spores are globose to subglobose, (17–)32(–52) µm in diameter, rarely egg-shaped, oblong to irregular, 17–38 µm × 19–43 µm. The single spore wall of G. indicum consists of two hyaline layers: a mucilaginous, short-lived, thin outer layer staining pinkish to pink in Melzer's reagent and a laminate, smooth, permanent, thicker inner layer. Glomus indicum was found in the rhizosphere of Euphorbia heterophylla  L. naturally growing in coastal sands of Alappuzha in Kerala State of South India and Lactuca sativa  L. cultivated in Asmara, Eritrea, North East Africa. In single-species cultures with Plantago lanceolata  L. as the host plant, G. indicum formed vesicular-arbuscular mycorrhiza. Molecular analysis of the phylogenetic position of G. indicum based on both SSU and ITS rDNA sequences showed the fungus to be a new species with its own cluster. Besides the sites where the spores were observed, sequence types belonging to the G. indicum cluster were documented from environmental samples mainly in the USA, Estonia, and Australia, suggesting the wide occurrence of the species. A key to all known species of the Glomeromycota producing hyaline to light-coloured glomoid spores is provided.