Role of Chitinolytic Enzymes and Volatile Compounds Produced by Endophytic Bacteria in the Inhibition of Mango ( Mangifera indica L.) Root Rot Pathogens

Endophytic and rhizobacteria isolated from different crops of Goa were studied for the chitinolytic activity and inhibition of fungal pathogens. Fifty-eight isolates were screened in vitro against three fungal pathogens, ., Macrophomina phaseolina, Rhizoctonia solani and Sclerotium rolfsii which cause seedling and graft mortality in mango nurseries. Results indicated that 40% of the isolates effectively inhibited the growth of all the three pathogens and 34% inhibited the growth of M. phaseolina and S. rolfsii under in vitro conditions. Chitinolytic ability of the isolates was tested by growing them in minimal synthetic medium with 0.2% colloidal chitin. Twelve isolates effectively utilized colloidal chitin as a sole carbon source for their growth. Quantitative chitinase assay revealed that the isolates produced significant amounts of chitinase in the minimal medium and the crude chitinase extract of nine endophytic (EB65, EB69, EBh11, EC2, EC2a, EC14, EC18, ESC4, ET14) and three rhizobacteria (IISR6, PDBC-AB2, RBh42) inhibited the mycelial growth as well as sclerotial germination of R. solani and S. rolfsii. Quantitative assay of chitinase showed that three endophytic bacteria (EBh11, EC18 and EC14) showed maximum chitinase activity. Chitinolytic bacteria reduced the population of all the three fungi when introduced into the soil. Further, most of the isolates produced IAA and solubilized inorganic phosphate in the medium. This study reveals that chitinolytic bacteria, especially endophytes with growth promoting mechanisms, could be better biocontrol agents in the suppression of soil borne phytopathogens.