An antagonist of Caenorhabditis elegans controls root-knot disease and promotes tomato plant growth

ABSTRACT Continuous cropping often leads to plant diseases caused by root-knot nematodes (RKN). Owing to the difficulty in laboratory culture of RKN, microbial biocontrol agents are mainly screened for through contact killing assay, which requires a substantial effort to acquire RKN. This study was undertaken to verify the feasibility of using Caenorhabditis elegans – a model nematode that can be easily grown in the laboratory – to screen for microbial antagonists against RKN. Tomato (Solanum lycopersicum L. cv. Houpi Maofen 802) plants were grown in pots containing RKN-infested soil with and without inoculation of an antagonistic actinobacterial strain, designated Streptomyces albidoflavus T4. Exposure to T4 culture filtrate that contained catecholate siderophore and indole acetic acid resulted in a mortality rate of 95.4% for C. elegans and increased seed vigor by 113% for tomato. While root rotting rate and RKN incidence decreased following T4 inoculation, plant survival rate and stem diameter increased correspondingly. The root-associated microbiota of inoculated plants were optimized, as indicated by increased proportions of potentially beneficial bacteria (e.g. Bacillus amyloliquefaciens) and decreased proportions of pathogenic fungi (e.g. Fusarium oxysporum). The results demonstrate the outstanding performance of S. albidoflavus T4 to control root-knot disease and benefit tomato plant growth through multifaceted mechanisms.