Isolation and characterization of chitinolytic rhizobacteria for the management of Fusarium wilt in tomato

Sixty-three chitinase producing rhizobacteria (CRB) were isolated from 57 rhizospheric soil samples of tomato (Lycopersicon esculentum Mill.) growing in different regions of Karnataka, India. Among these, 13 CRB isolates were selected based on their ability to produce chitinase, colonize roots of tomato seedlings and reduce Fusarium wilt incidence. Four of these isolates produced statistically higher levels of chitinase and also zone of clearance/colony size (CZ/CS) ratios. One Bacillus subtilis isolate (CRB20) substantially reduced the severity of Fusarium wilt under greenhouse conditions. Combined application of chitin or crude fungal cell wall (CFCW) along with this isolate, substantially enhanced the ability of the isolate to colonize tomato roots and reduced the severity of Fusarium wilt. Under greenhouse conditions, amendments of chitin and CFCW along with isolate CRB20 significantly enhanced plant height, fresh weight, number of fruits per plant and average weight of fruit compared to the untreated control. The study clearly established the significance of CRB isolates and chitin/CFCW amendment in promoting plant growth and suppression of Fusarium oxysporum, and indicated the possibility of their use for Fusarium wilt management in tomato cultivation.