Screening Of Meloidogyne Incognita Biocontrol Bacteria And Research On Its Influencing Factors

Meloidogyne incognita is one of the most important diseases of crops and causes serious economic losses.Chemical pesticides can not satisfy people’s needs because of their potential dangers to people and environment.Endophytic bacteria show great potential against M.incognita by reason of the unique advantage of natural environment,but they are easily affected by environment and that restricts their application.This study was designed to screen endophytic bacteria against M.incognita and research their influence factors of colonization and biocontrol effect.Primary screening for gelatinolytic activity through gelatin selective media,secondary screening for nematicidal activity of culture supernatant and bacterium suspension by co-culture with second-stage juveniles(J2)and in vivo screening for testing effect in pot experiment on tomato were used for screening endophytic bacteria against M.incognita.Candidate isolates were evaluated for growth-promoting effect and colonization ability by pot experiment on tomato.Finally the isolate with high biocontrol effect,growth-promoting effect and colonization ability was further evaluated in disease nursery and its colonization ability and biocontrol effect was investigated under different conditions of inoculum densities,inoculation methods,soil water content,soil pH,soil texture,fertilization and metal ions in pot experiment.Morphology and 16s rRNA was used for bacteria identification.Nineteen gelatinolytic isolates were screened out from 59 endophytic bacteria,among them,H1,SHI and E62 showed the highest gelatinolytic activity.The highest corrected mortality was observed with culture supernatant of ZC13(81.11%)and culture supernatant of Q1(52.76%).Four candidate isolates Q1,LA1,H1,and SHI were obtained with an inhibition rate of egg masses and galls more than 68%in pot experiment.All the four candidate isolates showed growth-promoting effect on tomato and colonized in rhizosphere soil with a population about 106 cfu/g,while only Q1 and SHI could colonize in tomato roots with a population about 104 cfu/g and Q1 showed the highest colonization ability.Biocontrol agent made from Q1 not only reduced M.incognita juveniles in roots by 68.75%but also promoted tomato growth in disease nursery.Q1,LA1,H1 and SHI were identified as Lysinibacillus sphaericus,Pseudomonas vancouverensis,Bacillus subtilis and B.cereus.High inoculum densities,inoculation through pouring the wound roots and 30%soil water content could increase the colonization in tomato roots;there was a positive correlation between biocontrol effect and colonization ability;high inoculum densities,inoculation through pouring the wound root,30%soil water content,neutral soil,clay loam,chemical fertilizer except kalium fertilizer and Ca2+ contributed to the control effect against M.incognita.This study indicates that endophytic bacteria have huge potential to control M.incognita and their colonization and effect can be stabilized or improved through changing conditions.