Trichoderma Collection And Its Function To Promote Growth Of Syringa Oblata And Induce Resistance Against Powdery Mildew Disease

Trichoderma,as an internationally recognized biological control fungus,can prevent and control pathogenic fungi by means of hyperparasitism,competition and resistance,which also can improve the immunity of host plants by improving the systemic resistance of host plants.Syringa oblata,the Harbin city flower,is damaged by S.oblata powdery mildew which will not only affect its ornamental value,but also affect the health of trees.However,chemical control is usually adopted to prevention and control powdery mildew,so it's urgent to find an environmentally friendly biological control method.In this study,biological control of powdery mildew was carried out by using Trichoderma which was collected from soil samples around the S.oblata roots.A total of 181 Trichoderma strains were isolated from 16 soil samples in District 8 of Harbin city.According to their morphological characteristics on PDA medium test tubes,181 Trichoderma strains were divided into 44 groups,and 1 strain was selected from each group for morphological and molecular biological identification.A total of 10 species of Trichoderma have been identified,which respectively are T.pseudoharzianum,T.afroharzianum,T.atroviride,T.viridescens,T.virens,T.brevicompactum,T.asperelloides,T.veluinum,T.hamatum and T.longibrachiatum.Among them,T.pseudoharzianum and T.afroharzianum were the dominant species with 46 and 41 strains respectively,and the inferior species were T.velutinum and T.brevicompactum with 2 and 1 strains respectively.Strains T.pseudoharzianumT1(TpseT1),T.afroharzianumT52(TafrT52)and T.asperelloidesT57(TaspT57)were screened for solid fermentation with large spore production,fast growth rate and good biocontrol effect.Formula of solid medium is rice husk:wheat bran=4:1,add 1%ferrous sulfate and 75%water to stir,then plate and seal in an environment of 28? for 5 days,the spores yield can reach 1 X 107 spores/g fermentation material.However,?inhibition occurred in all three Trichoderma strains when they were cultured in two or three confrontations.Furthermore,strain TafrT52 showed strong inhibition to strains TpseTl and TaspT57,with inhibition rates of 57%and 59%,respectively,reaching over 50%.And when the three Trichoderma species were co-cultured,the inhibition rate of each other reached more than 60%.Therefore,the three Trichoderma species can't be used together.Potted seedlings were watered by Trichoderma agents to study the growth promotion of Trichoderma on S.oblata seedlings.The results showed that TpseT1,TafrT52 and TaspT57 all promoted the increase and growth of the lateral roots of S.oblata seedlings at 15d and 30d,and the effect was more obvious with the increase of time.After treatment with TpseTl and TafrT52 agents for 7 days,the chlorophyll content was 1.58mg/g and 1.82mg/g,respectively,which significantly lower than that of the control leaves at 2.28mg/g.It is caused by negative regulation of Mg chelatase H subunit CH80451 gene in the middle stage of chlorophyll synthesis and chlorophyllide a oxygenase CA67767 gene in the later stage.The adult trees,with powdery mildew,were sprayed with the fermented Trichoderma agent to explore the biocontrol effect of Trichoderma agent on S.oblata powdery mildew.The results showed that the three Trichoderma agents could control powdery mildew,but in different ways.After TafrT52 treatment for 9 days,compared with the control group,the abscisic acid(ABA)content and catalase(CAT)activity of the leaves increased by 42.40ng/mL and 216.80nmol/min/g,respectively.After treatment with TaspT57 for 9 days,ABA content increased by 33.54ng/mL and malondialdehyde(MDA)content decreased by 1.81nmol/g.After TpseTl treatment for 9 days,CAT activity of diseased leaves was increased by 81.22nmol/min/g,MDA content and incidence of disease in the leaves were decreased as well.Therefore,both TafrT52 and TaspT57 strains can prevent and control S.oblata powdery mildew by promoting leaf fall,new leaf germination,reducing peroxides content and so on.TpseTl strain can not only reduce the content of peroxides in diseased leaves but also reduce the incidence of disease leaves.Trichoderma spray can restore the withered and constricted guard cells to full size.At the same time,after sprayed Trichoderma agent,stomatal SL/SOL value can be increased,stomatal closure can be promoted to prevent pathogenic fungi from invading plant cells,and finally achieve the purpose of disease resistance and plant protection.In conclusion,Trichoderma isolated from the soil samples of lilac roots had good growth promoting effect on S.oblata seedlings,and had good control effect on S.oblata powdery mildew,and different Trichoderma strains act in different ways.