Screening and Identification of Siderophore-Producing Endophytic Bacteria from Tomato Roots Infected by Root-Knot Nematodes

Tomato plants are highly sensitive to iron deficiency stress and are often subjected to combined infection by root-knot nematodes and soil-borne pathogenic bacteria such as Ralstonia solanacearum. To explore the resources of siderophore-producing endophytes and obtain biocontrol strains against root-knot nematodes with the potential to antagonize pathogens and mobilize soil nutrients, the Chrome Azurol S（CAS）assay was used in this study to determine the siderophore-producing capacity of 179 tomato root endophytic bacterial strains previously isolated from root-knot nematode-infected tomato roots in our laboratory. The results showed that 20 strains with stable siderophore secretion activity were obtained from the 179 tested strains, among which 11 strains exhibited siderophore activity at moderate positive level or above. Molecular identification and sequence analysis indicated that the 11 high siderophore-yielding strains were assigned to genera including Bacillus, Lysinibacillus, Brevibacterium, Xanthomonas and Rhizobium. Among them, the genus Bacillus was the most dominant group, accounting for 63.6% of the high-yield strains. This study enriches the resource pool of endophytic siderophore-producing bacteria from plant sources, and provides a reference for further research on the interaction mechanisms among plant beneficial bacteria, Ralstonia solanacearum and root-knot nematodes, as well as the development of novel nematode biocontrol agents with pathogen-antagonistic functions.