Persistence of introduced Glomus intraradices in the field as influenced by repeated inoculation and cropping system

We studied the persistence of an introduced vesicular-arbuscular mycorrhizal (VAM) fungus in the field under the influence of a mycorrhizal host, a non-mycorrhizal host, and when the field was left fallow. There was a significantly greater, build-up of the mycorrhizal fungus in plots cropped with mycorrhizal hosts (finger millet or field beans) compared to plots cropped with a nonmycorrhizal host (mustard) or left fallow. Glomus intraradices, the introduced fungus, was further monitored by the electrophoretic mobility of the isozymes of malate dehydrogenase extracted from the resting spores of the fungus. The zymogram from G. intraradices spores showed three distinct isozyme bands: 1,3 and 7. A zymogram of malate dehydrogenase spores isolated from plots inoculated with G. intraradices for three seasons exhibited similar bands. Spores isolated from plots inoculated with G. intraradices for one or two seasons showed only one weak band, corresponding to isozyme band 7. The results indicated that the introduced fungus persisted in the field for only one season.