Ultrastructural studies on the interaction between Bacillus subtilis MBI 600 (Integral) and the rice sheath blight pathogen, Rhizoctonia solani

The present study evaluated interactions of the biological control agent Bacillus subtilisstrain MBI 600 (Integral®) and Rhizoctonia solani, the rice sheath blight pathogen, through scanning electron microscopy (SEM). Ultrastructural effects related to antibiosis were studied by dual culture of B. subtilis (MBI 600) and R. solani on potato dextrose agar (PDA) plates. Hyphal growth near the inhibition zone was processed. To study the effects of hyperparasitism on fungal ultrastructure, Integral was sprayed on R. solani mycelia and observations were made three days later. Interactions of B. subtilis (MBI 600) and R.solani in planta were determined by spraying detached rice leaves with B. subtilis (MBI 600) and then inoculating with sclerotia of R. solani. In addition, sclerotia were dipped in Integral for 24 h, and cut sections were then observed. Overall the results indicate that B. subtilis (MBI 600) caused loss of structural integrity, shriveling, abnormal coiling, and lysis of the R. solani hyphae due to antibiosis and hyperparasitism in dual culture assays. On rice leaves, B. subtilis (MBI 600) also caused abnormal coiling, shriveling, and break down of hyphae. Sclerotia of R. solani dipped in Integral resulted in colonization of B. subtilis(MBI 600), maceration, and fragmentation of inner walls. Our results suggest that B. subtilis (MBI 600) from the product Integral was highly effective in suppressing R. solani