Isolation and characterization of nodules endophytic bacteria Pseudomonas protegens Sneb1997 and Serratia plymuthica Sneb2001 for the biological control of root-knot nematode

Root-knot nematode disease, caused by Meloidogyne spp., is one of the most serious soil-borne diseases for vegetable industry worldwide. A total of 448 endophytic bacteria isolates were obtained from root nodules and screened for the potential biological control activity against M. incognita in the field and pot under the greenhouse conditions. Strain Sneb1997 and Sneb2001 were screened with high biocontrol efficacy against M. incognita and identified as Pseudomonas protegens and Serratia plymuthica by morphology analysis, physiological biochemical test and biomolecular assay, respectively. Furthermore, 24 h after treatment, P. protegens Sneb1997 and S. plymuthica Sneb2001 showed high lethal effect on the second stage juveniles of M. incognita with mortality rate were 87.78% and 92.67% and inhibited egg hatching significantly (P < 0.05) with the hatch inhibition rate of 87.76% and 82.86%, respectively. Meanwhile, P. protegens Sneb1997 was effective in improving seed germination and S. plymuthica Sneb2001 did not affect seed germination. Then, the stability and efficiency of M. incognita control by P. protegens Sneb1997 and S. plymuthica Sneb2001 was further assessed in greenhouse and in the field in 2018 and 2019. The results of pot experiment showed that the metabolites of P. protegens Sneb1997 and S. plymuthica Sneb2001 both significantly (P < 0.05) decreased the number of root galls and egg masses of root and P. protegens Sneb1997 significantly (P < 0.05) promoted the growth of tomato plants. The results of field experiments demonstrated that two tested strains could significantly (P < 0.05) reduce gall index and significantly (P < 0.05) increased the tomato plant biomass. Confocal microscopy and colonization assay demonstrated that both endophytes could colonize in tomato roots and stems with a high density for a long period of time. In summary, our results demonstrate that endophytic P. protegens Sneb1997 and S. plymuthica Sneb2001 can be used as potential biological control agents to control root-knot nematode disease.

Automated summary

The study demonstrates that the endophytic bacteria Pseudomonas protegens Sneb1997 and Serratia plymuthica Sneb2001 have the potential as biological control agents against root-knot nematode disease, showing effective suppression of nematode population and promotion of plant growth.