Screening of Antagonistic Bacteria for Biocontrol Activities on Colletotrichum gloeosporioides in Papaya

Of the 27 antagonistic bacteria isolated from the fructosphere of papaya and screened by dual and concomitant test, four isolates of bacteria (B23, B19, B04 and B15) had high antagonistic activities against Colletotrichum gloeosporioides of papaya. Using the Biolog system, isolates B23 and B19 were identified as Burkholderia cepacia and B04 and B15 as Pseudomonas aeruginosa. Both B. cepacia and P. aeruginosa strongly inhibited the fungal growth by an average of 74.13 and 68.45%, respectively during in vitro screening on PDA medium. The bacteria also produced volatile as well as diffusible substances. Malformation of hyphae occurred in the presence of both bacteria. Hyphae were thickened, vacuolar and many swellings occurred in them or at the tips of hyphal strand. However, B. cepacia was found most efficacious biocontrol agent in this study. Total inhibition (100%) in spore germination was noted in presence of B. cepacia at 24 h after treatment. Filter sterilized culture filtrate of B. cepacia also significantly inhibited the mycelial growth (59.2%) and spore germination (100%) of the test fungus, thus suggesting that an antibiotic substance (s) may be produced by the bacterium. Therefore, in vitro activities of the B. cepacia against C. gloeosporioides of papaya in this study suggested that the bacterium can be an effective biological control agent.