Effectiveness Of Plant Phenolic Compounds On The Control Of Two Fruit Diseases And Its Action Mechanism

As one important secondary metablisms during growth and development of higher plants,phenolic compounds are not only involved into the plant induced resistance to pathogen,but also possed excellent antifungal activity against microorangism.In our study,the effectiveness of phenolic compounds on the control of gray mold of table grapes and litchi downy bilght was determined from the point of plant induced resistance and antifungal activity,also together with microscopic analysis,metabolite determination and moleculer assay to explore the action mechanism of phenolic compounds.Our results demonstrated the antifungal activity of phenolic compounds and highlight their potentials as an alternative strategy in the control of grape gray mold and litchi downy blight.The main results listed as follows:1.The effectivess of fulvic acid on the control of gray mold of table grapes was determined and the results indicated that the application of fulvic acid significantly increased the disease resistance of table grapes against Botrytis cinerea.Then,the action mechanism of fulvic acid against gray mold was explored by using the method of qRT-PCR and metabolites analysis,the results showed the fulvic acid treatment significantly induced the expression of genes involved into phenylpropanoid pathway,improved the activities of enzymes related to phenylpropanoid pathway in the table grapes and induced the accumulation of flavonoids,including flavone,flavonol and flavanone.2.The antifungal effect of 18 natural or synthetic phenolic compounds purchased from commercial suppliers,including simple phenolic,phenolic acids,stilbenes and flavonoids,were determined on four gray mold strains by an in vitro agar dilution assay.Overall,seven phenolic compounds were effective on inhibiting B.cinerea growth and were selected to test their activity on conidial germination as well as in vivo application on grape berries.Pterostilbene showed the highest antifungal activity and greatly reduced the growth of the mycelia,caused hyphae deformation,suppressed conidial germination of B.cinerea,and completely inhibited the germination of conidia at the concentration of 50 mg/L.Furthermore,treatment of grape berries with pterostilbene and piceatannol significantly reduced the disease incidence and severity.3.The synergistic antifungal activity of resveratrol in combination with pyrimethanil against pyrimethanil-resistant B.cinerea was evaluated in vitro and the results indicated that the combination of resveratrol and pyrimethanil showed excellent synergistic interactions according to LA theory.Significant synergistic values were recorded by the two-drug combination on the suppression of mycelial growth and conidia germination of B.cinerea.The combination of resveratrol and pyrimethanil caused malformation of mycelia.Moreover,the inoculation assay was conducted on table grapes and consistent synergistic suppression of the two-drug combination was found in vivo.4.Here,the method of fluorescent staining assay,microscopic analysis and biochemistry technology were used to explore the action mechanism of pterostilbene against B.cinerea,the results indicated that pterostilbene significantly damaged the plasma membrane and organelles,caused significant deformation of hyphae and conidiophore.Up-regulation of laccase gene Bclccl and Bclcc2 were observed in B.cinerea treated with pterostilbene,together with the increasing production of laccase activity.5.In this study,eight phenolic compounds(catechol,resveratrol,piceatannol,pterostilbene,catechin,naringenin,quercetin and luteolin)were selected to determine their effect on the sporangia germination of P.litchii,and pterostilbene exhibited strongest inhibition activity,with inhibition rate of 100%in the treatment of pterostilbene at 32 mg/L,and the concentration inhibiting 50%of zoospore release(IC50 value)was evaluated to be 6.8 mg/L.Then,the effectiveness of pterostilbene on the control of litchi downy blight and its action mechanism was investigated.The results showed that pterostilbene inhibited the mycelial growth of P.litchii and induced deleterious morphological modifications and ultrastructural alteration,including deformation and shrinking of mycelia and sporangia,the damage of cell wall,plasma membrane and organelles.Pterostilbene application significantly reduced the decay of litchi fruit and leaf caused by P.litchii,with the decay index reduction up to 48.6%and 88.0%,respectively.Moreover,peel browning of litchi caused by P.litchii reduced from 3.5 to 1.8 after treated with 1600 mg/L pterostilbene.