| Meloidogyne incognita,which represents the most important pathogenic nematodes in China,can cause serious losses in both the yield and quality of many crops.The endophytic Bacillus cereus BCM2 strain showed remarkable control effects on M.incognita.The efficiency of biocontrol agents is closely related to the soil ecological factors in the practical application.This study was designed to explore the soil factors influencing the biocontrol efficiency of BCM2 and the factors which enhance the BCM2-mediated tomato defense,so as to provide the theoretical basis for the biocontrol of M.incognita.BCM2 strain,which isolated from the plant,its colonization and growth in the roots of tomato are important for the biological control efficiency.The bacterial suspension of BCM2 strain was inoculated with the tomato root which grew in the isolated disease nursery under field condition to determine its colonization dynamics and biocontrol efficiency.The results showed that BCM2 strain can colonized in the roots during the whole life of tomato,and its colonization in 40 d after inoculation showed a tendency of slow decline,and then basically stabilized.By the end of the growth period of tomato,the population of BCM2 strain in the rhizosphere soils and roots of tomato were 5.86 log cfu g-1 and 3.38 log cfu g-1 respectively;The decrease rate of the eggs and larvae in tomato roots were 43.19%and 37.07%compared to the untreated control respectively,and there was an increase in the tomato yield of 47.4%.These results prove that BCM2 strain can colonize tomato roots for long periods of time and had a significant reduction in the population of M.incognita in tomato.BCM2 strain was tagged with streptomycin resistance,and the influence of different soil types,pH,water content and organic matter content on the colonization and biocontrol efficacy of BCM2 strain were investigated through pot experiments.The results showed that the population in tomato roots of BCM2 strain in sandy soil was significantly higher than that in clay and loam,and the biocontrol effects of BCM2 strain was no difference between different types of soil.When the soil pH was 7,the colonization of BCM2 strain in tomato roots and the control effects against M.incognita were significantly better than pH 5 and 9.When the soil water content was 25%,BCM2 strain showed the best colonization in tomato rhizosphere soils,and the gall index of tomato was significantly less than 15%and 35%.Rich organic matter content was conducive to a reduction in the number of M.incognita 2nd stage juveniles(J2s)in soil.The results of Split-root experiments showed that BCM2-mediated induced systemic resistance(ISR)in tomato may be enhanced by M.inconita.Further determination of BCM2-mediated ISR in tomato was enhanced by M.incognita through the activity of phenylalanine lyase(PAL)in tomato roots.The induction substance that enhanced PAL activity during the M.incognita invasion were screened from the content of M.incognita,galls and the secretions of M.incognita,the results showed that the secretions of M.incognita could induce the increase of PAL.And the analysis of M.incognita secretions was conducted by LC-MS/MS,a total of 25 proteins were identified and 12 of them were reported that involved in the nematode parasitic process.However,the specific protein of enhanced BCM2 mediated tomato defense still needs to be further confirmed.The B.cereus BCM2 strain has remarkable effects in controlling the M.incognita,and the biocontrol efficiency was influenced by soil pH,water content and organic matter content.Moreover BCM2 strain mediated tomato defense has close interaction with M.incognita,and these factors can be used to provide a basis for its development and application. |
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