Evaluation of indigenous rhizoplane Bacillus and Pseudomonas species for eco-friendly management of red rot in sugarcane

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ABSTRACT The management of Colletotrichum falcatum, an incitant of sugarcane red rot disease is thought to be feasible with the implementation of biological control. Although many fungal antagonists against C. falcatum were documented, only few investigations have been done to reveal the antagonistic potential of native rhizobacteria. In this line, the present study revealed the biocontrol potential of 40 rhizoplane bacterial isolates of Bacillus and Pseudomonas species against C. falcatum. In a direct confrontation test, six isolates SRP3 (44.26%), SRP19 (80.78%), SRP20 (69.81%), SRB2 (65.74%), SRB4 (54.81%) and SRB20 (80.37%) had greatly impeded the growth of C. falcatum. The test fungal growth pattern varied in the interaction zone, as evidenced by hyphal tip shearing, hyphal wrinkling and thinning, protoplasm disintegration, and hyphae clustering during microscopy. Further, these potential six isolates substantially reduced pathogen growth in indirect and remote confrontation tests, attributing to the antimicrobial activity of non-volatile and volatile compounds secreted by the rhizobacteria, respectively. Under greenhouse milieu, four (SRB20>SRP19>SRB2>SRP20) of the six isolates were effective in decreasing pre-emergence mortality and post-emergence seedling mortality as a result of sett bacterization in C. falcatum inoculated pots. In conclusion, due to their ability to suppress disease in both in-vitro and in-vivo conditions, the native rhizobacterial isolates Bacillus vallismortis strain SRB20, Pseudomonas chlororaphis subsp. aurantiaca strain SRP19, Bacillus inaquosorum strain SRB2 and Pseudomonas aeruginosa strain SRP20 were considered the most promising isolates for enhancing plant health. In order to find an effective bacterial antagonist against C. falcatum, twenty isolates of indigenous rhizoplane Bacillus and Pseudomonas species were tested against redrot pathogen under three tier system i.e., Direct, Indirect and Remote confrontation. Then the disease suppressing ability was assessed by sett bacterization under greenhouse conditions. CF –Culture filtrate. PEM – Pre-emergent mortality. PESM- Post-emergent seedling mortality.