Control ofRhizoctonia solani andSclerotium rolfsii in the greenhouse using endophyticBacillus spp.

Abstract

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 fromSinapis (isolate no. 65) inhibited growth ofRhizoctonia solani, Pythium ultimum andSclerotium rolfsii and also exhibited chitinase activity.Bacillus subtilis from onion tissue culture (isolate no. 72) inhibitedR. solani andP. ultimum growth.B. cereus from cauliflower (isolate no. 78) inhibited growth ofR. solani. B. pumilus from sunflower (isolate no. 85) inhibited growth ofR. solani andS. 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 withB. cereus (isolate no. 65),B. subtilis (isolate no. 72) orB. pumilus (isolate no. 85), disease incidence caused byRhizoctonia solani was reduced in the greenhouse by 51%, 46% and 56%, respectively. In bean seedlings inoculated withB. subtilis (isolate no. 72),B. cereus (isolate no. 78) orB. pumilus (isolate no. 65), disease incidence caused bySclerotium 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.