Synergistic effect of arbuscular mycorrhizal fungi and Bacillus subtilis on the biomass and essential oil yield of rose-scented geranium (Pelargonium graveolens)

Four different arbuscular mycorrhizal (AM) fungi, Glomus aggregatum, Glomus fasciculatum, Glomus intraradices and Glomus mosseae, were used alone and in combinations with Bacillus subtilis to evaluate their capability to increase the productivity of geranium. Mycorrhizal treatment increased the growth and total biomass invariably over non-mycorrhizal control plants. In AM alone treatment, the best result was obtained for G. mosseae treatment, where 380.9 and 335.3 g fresh herb yield per pot was recorded in 2005-2006 and 2006-2007, respectively, an increase of 75.3 and 85.9% over controls. Plants inoculated with B. subtilis alone yielded 287.8 and 252.3 g fresh herb, an increase of 32.4 and 39.9% over uninoculated controls. However, B. subtilis in combination with G. mosseae produced the highest herb yield, i.e. 410.8 and 347.8 g herbs pot(-1), an increase of 89.4 and 92.9% over untreated controls. The field experimental data validated the results of the pot experiment. Treatment with G. mosseae alone increased herb yield by 49.4%, whereas in combination with B. subtilis, it increased herb yield by 59.5%. Treatment with AM fungi and B. subtilis did not affect the essential oil content of the plant, but total oil yield was significantly increased because of the increase in biomass production.