Effects of Serratia nematodiphila CT-78 on rice bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae

• Serratia nematodiphila CT-78 is a bio-control agent of rice bacterial leaf blight.
• The control mechanisms involve antibiosis and siderophore production.
• Seed coating and foliar spraying are the most effective application methods.

Bacterial leaf blight (Xanthomonas oryzae pv. oryzae) causes severe losses in many rice cultivation regions of the world. This study aims at isolating and identifying antagonistic soil bacteria to be used for biological control of this disease. Among the 830 bacterial isolates collected from rice fields in the Mekong Delta of Vietnam, CT-66, CT-78 and CT-88 from Can Tho city exhibited strong antagonistic effects against the pathogen. Their effects involved antibiosis (CT-66, CT-78 and CT-88) and siderophore production (CT-78). Seed soaking applications of the three isolates did not result in any observable adverse effects on rice seed germination and development. Under greenhouse conditions where rice plants were artificially inoculated at 45 days after sowing, the applications including foliar spraying at 14 days before inoculation (107 CFU/mL), seed coating (107 CFU/mL) and soil drenching (108 CFU/mL) with CT-78 showed the best and most extended protection among the three isolates tested. CT-78 was identified as Serratia nematodiphila based on its 16S rRNA gene sequence combined with its morphological and biochemical characteristics. Under field conditions, similar effects of S. nematodiphila CT-78 against bacterial leaf blight were observed. Foliar spraying at 14 days before inoculation and seed coating were the most effective treatments, resulting in a reduction in percent infected tillers (up to 83%), percent infected leaves (up to 88%) and disease severity (4.5-folds lower) and increases in grain yield and quality. Thus, S. nematodiphila CT-78 shows its potentials for large-scale applications to bio-control bacterial leaf blight in rice fields.