Control of Rhizoctonia solani and Sclerotium rolfsii in the greenhouse using endophytic Bacillus spp.

Isolates of different endophytic bacteria were recovered from surface-disinfected seeds obtained from commercial companies, plants in the field and tissue culture. The bacteria were isolated from seeds after stringent surfacedisinfection. Pseudomonas fluorescens (isolate no. 14) from bean inhibited growth of all fungi tested and was fluorescent on King B medium. Bacillus cereus from Sinapis (isolate no. 65) inhibited growth of Rhizoctonia solani, Pythium ultimum and Sclerotium rolfsii and also exhibited chitinase activity. Bacillus subtilis from onion tissue culture (isolate no. 72) inhibited R. solani and P. ultimum growth. B. cereus from cauliflower (isolate no. 78) inhibited growth of R. solani. B. pumilus from sunflower (isolate no. 85) inhibited growth of R. solani and S. rolfsii. B. cereus (isolate no. 65) was introduced into cotton, and by using radioactive labelling we found that it was present for 16 days in the root-stem junction. It is most likely that these bacteria were still found 72 days after their introduction in the root and stem, at levels of 2.8·10⁵ and 5·10⁴ cfu g^-1 fresh weight, respectively, when selective medium was used. There was no difference between control and treated plants in their height or in the fresh weight of roots, stems and leaves. When cotton seedlings were inoculated with B. cereus (isolate no. 65), B. subtilis (isolate no. 72) or B. pumilus (isolate no. 85), disease incidence caused by Rhizoctonia solani was reduced in the greenhouse by 51%, 46% and 56%, respectively. In bean seedlings inoculated with B. subtilis (isolate no. 72), B. cereus (isolate no. 78) or B. pumilus (isolate no. 65), disease incidence caused by Sclerotium rolfsii was reduced by 72%, 79% and 26%, respectively, as compared to control. In both cotton and bean seedlings, these endophytes reduced the disease index more than 50%. These results indicate that endophytic bacteria can survive inside cotton plants and are efficient agents for biological control against plant pathogens under greenhouse conditions.