Identification and Mechanism of Strain X-20 for Biocontrol against Meloidogyne incognita
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.
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