Abstract:

Meloidogyne incognita is a major pathogen that affects vegetable crops, and currently, there are limited safe and efficient biological control options available. In this study, strain X-20 was isolated from soil where root-knot nematodes were present. When tested against second-stage juveniles (J2) of M. incognita, strain X-20 exhibited a mortality rate of up to 100% after 24 and 48 hours. The strain X-20 was identified as Pseudomonas fluorescens through various methods, including morphological, physiological, biochemical and molecular biological analysis. When 1 mg/mL fermentation broth of strain X-20 was used to treat J2 of M. incognita, the nematode body showed twisted and stiff changes, and the internal tissue decomposed. After 1 hour of treatment, the fluctuation frequency of the body decreased by 47.26%, the swing frequency of head and the bending frequency of the body also changed. After 24 hours of treatment, the body length of M. incognita J2 decreased 4.68%, while the stylet length and the hyaline tail length of M. incognita J2 increased by 7.64% and 83.9%, respectively. Meanwhile, the body fluids of M. incognita J2 leaked, and its conductivity increased with the increase of treatment concentration and time. After six hours treatment with 1 mg/mL methanol extract from fermentation broth, the sugar and glycerol content of J2 body increased by 39.10%, 66.67%, respectively; While the soluble protein content of J2 body 55.73% decreased compared to the control. In conclusion, the metabolites produced by strain X-20 were found to cause body fluid leakage, disrupt the body wall and internal structure of root-knot nematodes, and affect the metabolism of sugars, lipids, and proteins, ultimately leading to the death of M. incognita.

Key words: Pseudomonas fluorescens, metabolite, Meloidogyne incognita; control efficacy, biocontrol mechanism