Beneficial bacterial volatile compounds for the control of root-knot nematode and bacterial leaf blight on rice

Microbial volatiles can promote plant growth and suppress diseases, nematodes and insects. Our knowledge of the effects of microbial volatiles on monocots such as rice and its pathogens and pests is still incomplete. As part of a screening initiative for beneficial bacterial species, we identified three strains (Bacillus sp., Paenibacillus sp. and Xanthomonas sp.) lethal to the rice root-knot nematode (Meloidogyne graminicola). Using both in vitro and in planta dual-chamber pot experiments, we found that volatiles from the beneficial bacteria were lethal to M. graminicola J2s and significantly reduced infection of susceptible rice. We conducted similar in vitro and in planta experiments against rice bacterial leaf blight Xanthomonas oryzae pv. oryzae. Exposure to bacterial volatiles inhibited the growth of X. oryzae pv. oryzae by 50–60% in vitro, but did not impact infection in planta. Finally, we found that bacterial volatiles from Bacillus sp. and Xanthomonas sp. inhibited rice germination and seedling development in vitro but did not affect plant growth in planta. These findings suggest that volatiles from beneficial bacteria have the potential to control M. graminicola, but that high volatile concentrations may inhibit plant growth.