The Induction Of Induced Tobacco Systemic Disease Resistance And Its Mechanism By Trichoderma

Tobacco black shank disease is a typical and destructive soil borne disease caused by Phytophthora nicotianae during tobacco growt,it can occur at any stage of tobacco growth and has a wide range of occurrence,which may lead to crop failure in severe cases,causing huge economic losses to the tobacco industry.The control measures of tobacco black shank disease mainly rely on chemical control,but longterm chemical control will not only cause drug resistance of plants,but also cause many environmental problems,such as polluting the atmosphere,making the soil acidic,making water eutrophication and other ecological problems.Trichoderma spp.is a widely distributed microbial group with important biocontrol applications in the soil environment,due to its diverse biological control mechanisms,high efficiency and broad-spectrum,safety against various non target organisms,and environmental friendliness,it has become a widely used functional fungus.This article screened the most suitable tobacco varieties and Trichoderma growth promoting functional strains.by studing the interaction between six different varieties of tobacco and biocontrol Trichoderma.Through the screening of antagonistic strains between Trichoderma and three plant pathogens: Alternaria alternata,Phytophthora capsica and Phytophthora nicotianae,Trichoderma hamatum ACCC 31649 and Trichoderma harzianum ACCC 32808 were selected as broad-spectrum biocontrol experimental strains,and Trichoderma harzianum ACCC 32808 had an inhibition rate of 62.00% on Phytophthora nicotianae,with a control effect of 63.63% and 82.48%on Phytophthora capsica and Alternaria alternata,respectively.Clarified the colonization status of tobacco inoculated with two types of Trichoderma in the rhizosphere soil of different tobacco varieties by dilution plating procedure,using Trichoderma selective culture medium,and the effect of inoculation with Phytophthora nicotianae on the Colonization of Trichoderma.The results showed that the colonization of Trichoderma hamatum ACCC 31649 and Trichoderma harzianum ACCC 32808 in the rhizosphere soil of Hong Da tobacco variety after 30 days was 1.86×106spores/g soil and 9.38×105spores/g soil.The colonization of Trichoderma hamatum ACCC 31649 and Trichoderma harzianum ACCC 32808 in K326 tobacco rhizosphere soil for 30 days was 4.17×104spores/g soil and 2.47×105spores/g soil.Trichoderma has stronger colonization ability in Hong Da than K326.Simultaneously discovered their promoting effects on different tobacco varieties,the fresh and dry weight of Hong Da tobacco seedlings treated with spore suspension of Trichoderma hamatum ACCC 31649 were significantly increased,1.15 and 1.3 times higher than the control group.However,the promotion effect on the dry and fresh weight of K326 tobacco seedlings is not significant.Verified the indoor biocontrol effects of two Trichoderma species on different tobacco varieties through greenhouse pot experiments.After 2 days of inoculation with Trichoderma spore suspension,inoculate with Phytophthora nicotianae,the indoor control effects of Trichoderma hamatum ACCC 31649 and Trichoderma harzianum ACCC 32808 on tobacco black shank disease were 44.6% and 51.74%,respectively.And further clarified the physiological,biochemical,and molecular mechanisms of Trichoderma harzianum ACCC 32808 strain in inducing tobacco resistance.the activities of Catalase(CAT),peroxidase(POD)and Superoxide dismutase(SOD)in tobacco leaves were determined,the results showed that Trichoderma can significantly induce an increase in the activity of disease-resistant enzymes in tobacco.The induction increased the CAT,POD,and SOD of the leaves of Hong Da by 1.42,2.49,and 1.17 times,respectively;The CAT,POD,and SOD of K326 leaves increased by 2.15,2.29,and 1.15 times,respectively.Trichoderma harzianum ACCC 32808 treatment of Hong Da variety can induce upregulation of NPR1 expression by 2.03-fold,PR1 a up-regulated by 100.90 times in the salicylic acid metabolism pathway,Two key genes in the ethylene pathway,EFE upregulated by 10.31 times and ET upregulated by 3.19 times;The Jasmonic acid pathway gene PDF1 was up-regulated by 2.06 times;Active oxygen related gene AO was up-regulated by 5.35 times,and activated galactosidase gene Nt SGT1 was upregulated by 1.86 times.Treatment of tobacco variety K326 with Trichoderma harzianum ACCC 32808 can induce upregulation of salicylic acid pathway NPR1 expression by 3.04-fold,but there was no upregulation of PR1 a gene expression.Two genes in the ethylene pathway,EFE upregulated by 2.21 times and ET upregulated by3.45 times;The expression of Jasmonic acid pathway gene PDF1.2 was up-regulated1.40 times;The expression of reactive oxygen species related gene AO was upregulated by 15.30 times;The activated galactosidase gene Nt SGT1 was upregulated 1.71-fold.This study screened functional strains that promote growth and resistance,combining the pathogenic situation of indoor tobacco black shank disease,revealed the induced resistance mechanism of Trichoderma functional strains to tobacco diseases,Provide a theoretical basis for the in-depth application of Trichoderma biocontrol bacteria in tobacco disease prevention and control.