Study On The Pathogenicity Of Different Matting Type Beauveria Bassiana Strains And Their Colonization In The Field

Beauveria bassiana is the one entomophagous fungus has been widely used toagainst Ostrinia furnacalis in the world,,and it’s an important member of agroecosystem,has good control effect to agricultural pests.B. bassiana has been applied tocontrol O. furnacalis by stalk piles covered1.33million hectare every year since last5years in Jilin province, producing significant economic, social and ecological benefits.This thesis aimed to improve breeding efficiency of B. bassiana strains and controlefficiency through proposed researches.To clarify the genetic background of B. bassiana strains is the prerequisite to carryout relevant research.Standard procedures based on molecular markers to distinguishmatting-type of B. bassiana strains were funded in this study.21were MAT1-1strains(GZ18,GZ19,GZ20) within23strains tested, GZ01was MAT1-1strain and GZ12were mixed strains.Study the biology of B. bassiana strains is a basic work of screening fine strains. Thebiological characteristic indicators including spores production, spores germination andcolony growth speed of GZ19and GZ01strains were compared. Colony growth speedand spores production of GZ01strain were both10%higher than GZ19strain. Thesetwo strains were significant differences in above two indicators.; the average sporesgermination rate of GZ19strain was (57.±8.6)%, and GZ19strain was (60±8.9)%.GZ19and GZ01strains were significant differences in colony diameter and sporesproduction, though there were no significant differences in spores germination.Standard toxicity bioassay method can accelerate the screening time and cycle.Thepathogenicity of B. bassiana against3rd instar larvae of O. fumacalis were assessedwith dose-response assays by Feeding and Dipping method respectively. No significantdifferences were observed among corrected mortality, LT50and LC50of the larvae bytwo methods under different spore concentrations of105cfu·L-1,106cfu·L-1,107cfu·L-1and108cfu·L-1in treatment groups. But the mortality of the larvae by Feeding methodwere significant lower than that of Dipping method in the control groups, respectively. It suggested that Feeding method is a sensitive method with alternative to Dippingmethod.B. bassiana strain had no significant differences in LT50between different instarlarvae by Feeding method,3rd instar larvae were ideal selection as test agents. Thepathogenicity of different spores mixed ration of GZ19and GZ01strains against3rdinstar larvae of O. fumacalis were assessed.The mortality of GZ01strain alone was6.5%higher than GZ19strain alone The mortality of larvae could reached86%usingGZ01strain. Equal mixed spores of the two strains showed synergies in pathogenicity.Definition of the pathogenicity of B.bassiana strains is important reference ofapplication of biological control agents. Transmission electron microscope(TEM) wastaken to observe the cuticle and mid-gut histopathological changes of5rd instar larvaeinfected by GZ19strain using Feeding and Dipping method respectively. It had beenrevealed unlike histopathological symptom under different infection way. B.bassianamainly infected larvae through cuticle by Dipping method, however, mid-gut infectionwas one possibly approach by Feeding method.Phenol oxidase is an important defense enzymes of insect against pathogen. It showedthat phenol oxidase activity had quicker response to injection method. Feeding anddipping methods were also taken to measure the changes of phenol oxidase activity.GZ01strain was more sensitive than GZ19strain and phenol oxidase activity ratereached its high peak in40h.Colonization of B. bassiana in O. fumacalis larvae and different parts of maizetissues under field condition were investigated. Results showed that B.bassiana couldcolonized as the endophytic fungi in tissues of maize, persistence of B.bassiana wereroots> stems> leaves, the detection rate was95%、75%and55%. GZ01strain was andominant endophytic strain,the detection rate was82.5%, in contrast to17.5%of GZ19strain. Colonization of B. bassiana had severely restrained the growth of O. fumacalislarvae,Endophytic B. bassiana presented potential control effect as a new approach inpest biological control.