Bacillus amyloliquefaciens as a Biocontrol Agent Improves the Management of Charcoal Root Rot in Melon

Seventy five bacterial strains were isolated from cucurbits rhizosphere and examined for antagonistic activities against Macrophomina phaseolina isolate 44, the causal agent of melon charcoal root rot disease. The results of screening strains including B2, B11, B12 and BKN showed high potential of antagonistic activities against the pathogen in laboratory experiments. Inhibition of mycelial growth varied from 54.3 to 62.22%, 39.43 to 54.82%, 78.52 to 100%, and 64.45 to 88.89% in dual culture, volatile metabolite, antibiotic production, and cell free culture tests, respectively. In greenhouse experiment, seed treatment with strain B2 significantly (P=0.01) controlled the disease by increasing plant growth indices including height, shoot and root fresh weight, shoot and root dry weight by 37.98, 36.27, 32.97, 34.44, and 30.39%, respectively, as compared to the control. The biochemical and physiological tests as well as gyrA sequence confirmed these four strains as Bacillus amyloliquefaciens. Results indicated that strain B2 could be an important new biological control agent for charcoal root rot disease of melon.