Gigaspora margarita was increased in pot culture using Sorghum vulgare ('Shallu'). Soil was treated with methyl bromide (102 mg/L) for 24 h or heat treated at 82 °C for 6 h and mixed with vermiculite. Tobacco (Nicotiana tabacum) NC 2326 was inoculated at transplating with 500 (in 1978) or 4050 (in 1979) azygospores per plant and fertilized at three levels. Positive responses in growth to inoculation and significantly greater numbers of spores were observed both years at only the lowest fertilization levels. In the 1978 test, frenching of tobacco occurred in only the low fertilization level. Significantly less frenching occurred in the mycorrhizal inoculated treatment than in the control.