Nematicidal potential of rhizobacteria against Meloidogyne graminicola in the rice-wheat cropping system

The rice-wheat cropping system (RWCS) is one of the most important cropping sequences for food self-security. In this RWCS, rice root-knot nematode, Meloidogyne graminicola is an emerging problem. To manage this nematode, the rhizospheric bacteria were isolated from three treatments using three media, NA, Kings’ B and TSA (Rice - Wheat - Crotalaria; Rice - Wheat - Mungbean; Rice - Wheat - Fallow) followed by RWCS. Out of six isolated bacteria, four bacteria showed the antagonist potential against M. graminicola. In vitro conditions, the bacteria isolated from fallow showed up to 31 % J2s mortality, 55-61 % in mungbean and 54-96 % in Crotalaria. The isolate, SRB7 showed 100 % juvenile mortality and 98.6 % hatching inhibition; finally, the isolates followed a pattern of SRB7 > SRB13 > SRB9 > SRB6 > SRB2 > SRB9. The bacterial isolates, SRB7 and SRB13, performed better than others in the attraction and penetration test. Through molecular characterization by 16s rRNA sequencing, the isolates SRB7, SRB13, SRB9 and SRBS6 were identified as B. subtilis (OL716087), B. cereus (OL716088), B. megaterium (OM816754) and Pseudomonas stutzeri (OL716089) in the soil collected from long-term RWCS fields. In the case of the pot study, these isolates decrease the nematode infestation by 83 % and increase plant growth by 82 % over the control. In the case of the pot study, these isolates decrease the nematode infestation by around 50 to 80 % over the control. The plant defence enzymes, PO, PPO and PAL activity reached a maximum on the sixth day and started to decrease. The long-term incorporation of green manure crop Crotalaria and mung bean in RWCS increases the beneficial soil microbes, suppressing the M. graminicola population and increasing the yield in the rice-wheat cropping system.