Molecular identification and biocontrol activity of sugarcane rhizosphere bacteria against red rot pathogen Colletotrichum falcatum

A total of 226 sugarcane rhizosphere-associated bacterial strains from the six different cultivars were screened against three pathogenic strains of C. falcatum (cfNAV, cfCHA, and cf8436) for the suppression of red rot disease. On the basis of mycelial growth inhibition in dual culture assay, 26 bacteria were selected for further characterization of morphology, biochemical activity, plant-growth-promoting (PGP) activity, antifungal potential and molecular identity by 16S rRNA gene sequence. On the basis of the 16S rRNA gene sequencing, it was found that the isolates belonged to proteobacteria (13), Firmicutes (10), and Bacteroides (3). The antagonistic bacteria tested for PGP traits revealed that 10 strains were able to solubilize tricalcium phosphate, 11 strains were able to produce siderophore, and 14 strains were able to grow in the N-free medium. The quantitative estimation of indole-3-acetic acid production was ranged from 21.58 to 66.31 μg/mL. On the basis of PGP and biocontrol traits, five strains Ochrobactrum intermedium (TRD14), Acinetobacter sp. (PK9), Bacillus sp. (RSC29 and KR91) and Escherichia sp. (VRE34) were further chosen for pot trial under greenhouse conditions on highly susceptible variety CoC671. The results showed that the pathogen-inoculated sugarcane plants were able to germinate but died within one month. However, the CoC671 inoculated with selected biocontrol strains found protected from disease and an increase in plant growth parameters on par with carbendazim fungicides. This study proves that the isolates identified in this study could be used as an alternative to chemical fungicides to control red rot pathogen of sugarcane plants.