Biological control of ragi blast disease by chitinase producing fluorescent Pseudomonas isolates

Blast disease caused by the fungus, Magnaporthe grisea , is among the most damaging diseases of rice and ragi leading to heavy crop losses worldwide. To avoid losses, farmers resort to indiscriminate applications of plant protection chemicals that also harm the ecosystem and lead to resistance buildup in the phytopathogens. Therefore, alternative eco-friendly strategies need to be evolved and put in place. The present study was thus undertaken to identify competent rhizobacteria having promising biocontrol activity against M. grisea infecting ragi. A total of 70 rhizospheric pseudomonads were isolated from different annual plants, of which 10 isolates showed maximum inhibition of two test isolates of M. grisea . Pseudomonas fluorescens isolate Pf-30 exhibited maximum inhibition (81.25 and 88.43 %) against the test pathogen, followed by Pf-53. Of all, 19 isolates were prominent in chitinase production with Pf-30 showing maximum efficiency (218.18 %) for enzyme production. In general, 25 °C temperature and pH 5.0 were optimum for enzymatic activity, although maximum activity (15.42 IU ml −1 ) by Pf-30 was recorded at pH 6.5 and 35 °C, followed by Pf-53 (4.48 IU ml −1 ). In - planta evaluation in polyhouse revealed that different pseudomonads could suppress the disease significantly when given as seed treatment and foliar spray. Maximum disease suppression was exhibited by Pf-47 and Pf-53 (82.77 and 82.06 %, respectively). Effect of three-factor (pathogen, variety, and pseudomonads) interaction revealed that all interactions, except pathogen x variety, contributed significantly.