Induced Systemic Resistance And Mechanism Of Cucumber To Botrytis Cinerea By Trichoderma

Trichoderma (Trichoderma spp.) are important biological control fungi which play animportant role in biocontrolling plant disease. A mass of researches indicate that theantagonistic properties of Trichoderma are based on the activation of multiple mechanisms.Trichoderma strains exert biocontrol against fungal phytopathogens not only by mechanismsof competition, mycoparasitism, antibiosis, but also by the mechanism of induced systemicresistance of plants. At present, the induced systemic resistance mechanism by Trichodermahas been made a certain progress, but still not completed. Studing it in-depth is beneficial toconstruct efficient biocontrol Trichoderma strains, and produce good effect agent ofTrichoderma. It is significant for controlling plant diseases. In this research paper, we selectedTrichoderma strains which can induced systemic resistance, identificated the strains bymorphological and ITS rDNA molecular identificated methods, studied the induced resistantmechanism, and constructed induced resistant technique protocol of Trichoderma initially.We selected the Trichoderma strains with induced systemic resistance to Botrytis ciner-ea on cucumber by plant bioassay from the antagonistic strains that kept in our laboratory.The results show that significantly different Trichoderma strains induced different controleffects by induced cucumber roots. Among them, strains of Tr-28and Tr-92have the bestcontrol effects,53.7%and56.0%respectively. The results indicate these two Trichodermastrains have strong induction systemic resistance on cucumber. The two Trichoderma strainswere identifed by morphological and ITS rDNA molecular identificated methods. Combiningthe results of these two identificated methods, Trichoderma Tr-92strain is Trichodermaatroviride, while Trichoderma Tr-28is Trichoderma spp.After inducing cucumber seedlings roots with Trichoderma Tr-28and Tr-92,wedeterminate the changes of POD, PPO, PAL, chitinase and beta-1,3-glucanase enzymesactivity in leaf, stem and root tissues. The results showed that POD, PPO, PAL, chitinase andbeta-1,3-glucanase enzymes activity in different tissues of induced group were significantlyhigher than those in control group. The Tr-28induced treatment group,the peak activity of POD, PPO, PAL, chitinase, beta-1,3-glucanase enzymes activity in leaf tissue are1.86,1.00,2.94,1.11,1.02times of that of the control treatment; the peak activity of POD, PPO, PAL,chitinase, beta-1,3-glucanase enzymes activity in stem tissue are1.00,1.15,2.01,2.66,1.17times of those in the control treatment; the peak activity of POD, PPO, PAL, chitinase,beta-1,3-glucanase enzymes activity in the root tissue are1.30,1.18,1.50,1.18,1.02times ofthose in control treatment.While the treatment group induced by Tr-92, the peak activity ofPOD, PPO, PAL, chitinase, beta-1,3glucanase enzymes activity in leaf tissue are3.61、1.44、3.94、1.34、1.39times of those in the control treatment; the peak activity of POD,PPO, PAL,chitinase, beta-1,3-glucanase enzymes activity in stem tissue are3.11、1.65、2.12、1.38、1.31times of those in control treatment; the peak activity of POD, PPO, PAL, chitinase, beta-1,3-glucanase enzymes activity in the root tissue are1.37、1.70、2.23、1.23、1.01times of thosein control treatment. Compared with the induced resistance ability of two Trichoderma strainsin different tissues of cucumber seedlings，the induction ability of Tr-92is even moresignificant.After inoculating with Trichoderma Tr-92in cucumber roots, the POD isozyme andpathogenesis-related proteins (PRS) in the cucumber leaves were examed by polyacrylamidegel electrophoresis analysis. The result showed that new POD isozyme was induced byTrichoderma Tr-92in cucumber leaves. These indicate that Trichoderma Tr-92has the abilityto increase expression of POD isozyme in cucumber leaves. The pathogenesis-related proteinbands were increased in cucumber leaves which mean that Trichoderma has the ability ofinducing potential defense gene expression in cucumber.Surveying the cucumber roots treated with Trichoderma by transmission electronmicroscopy of ultrathin sections, the picture revealed that Trichoderma can penetrate into theroot epidermal cells, enter into the cortex where cells are tightly packed.Tr-92can survive inthe cells root tissues.and leading large amounts of wall appositions just as callose andcellulose contained in the cells in the root tissues. The epidermal and cortical cell walls werestrengthened. So, the invasion by pathogens were decreased.Inoculated Trichoderma by different concentrations of spore suspension, differentintervals and other factors, we initially built the technique protocol induced resistance to Botrytis cinerea on cucumber by Trichoderma Tr-92, The results showed that inoculated withspores suspension with the concentration of106cfu/mL, challenged inoculation with Botrytiscinerea pathogens after3d induce, inoculate position at the roots of cucumber seedings whencucumber seedings with one leaf, were the best induced resistance of cucumber seedlings doaquire.