Arbuscular mycorrhizal fungi associated with green gram in south India

Field studies are necessary to understand the abundance and type of indigenous arbuscular mycorrhizal (AM) fungi present in the rhizosphere. Green gram [Phaseolus aureus Roxb. (= Vigna radiata var. radiata)] is a major pulse crop of South India. A field study was conducted to identify the AM fungi associated with green gram under field conditions in this region. The rhizosphere soil samples from these fields were analyzed for AM fungal spores. Glomus mosseae, Glomus microcarpum, Gigaspora margarita, and Scutellospora sp. were identified as the AM fungi associated with green gram. Glomus mosseae was the most frequent AM fungal associate identified in 81%, G. microcarpum and G. margarita in 24% each, and Scutellospora sp. in 5% of the soils studied. The range of distribution varied from a single species of AM fungus to three species belonging to two genera in one sample. Correlations of spore count and percentage colonization for all the AM fungi on the crop in the field, along with soil parameters like pH, N, P, and K were studied. Significant negative correlation (P < 0.01) was obtained between percentage colonization and P. The pH and N were positively correlated (P < 0.01) with K. The study indicates involvement of factors other than soil nutrients in the distribution and sporulation of AM fungi.