Main Data :
A field experiment was conducted to evaluate the benefit to growth of Allium cepa L. of inoculation with a mixed culture of indigenous arbuscular mycorrhizal (AM) fungi. Four locally adapted onion cvs. Pusa White Flat (PWF), Pusa White Round (PWR), Early Grano (EG) and Pusa Madhvi (PM) were grown at two phosphorus levels (25 and 50 kg P ha) in a P deficient alfisol. Inoculation significantly increased mycorrhiza formation over that caused by the level of native AM fungi present at the site. At harvest, all inoculated onion varieties showed higher values of bulb diameter, fresh weight, shoot dry matter, shoot P content and bulb yield than uninoculated plants. However, the magnitude of AM response for yield in a given onion variety was found to be different at different levles of P. This holds true in all the varieties tested. Inoculated plants tended to have greater bulb yield for varieties OM and OWR grown at 25 kg P ha. On the other hand, PWF and EG plants showed similar response at 50 kg P ha. The percent root length colonized by AM fungi between both the P levels of inoculated plants did not differ significantly. However, the extent of colonization varied among the varieties. The dependence of plants on mycorrhizal fungi for bulb production varied among the varieties grown at a particualr P. EG and PWF plant showed maximum dependence on AM at 50 kg P ha, where as PM and PWR plants exhibited a maximum MD at 25 kg P ha.