Biocontrol Mechanism Of Volatile Organic Compounds Of Hansenispora Uvarum On Postharvest Gray Mold Of Strawberry

Strawberry fruits are popular with people all over the world because of their delicious flavor and rich nutrition.However,the extensive occurrence of gray mould brought loss to strawberry planting and storage.Because yeast could produce volatile metabolites with antagonistic effect,it had been concerned by many researchers and was used to control postharvest diseases of fruits and vegetables.Our laboratory previous study found that the volatile compounds of Hanseniaspora uvarum had inhibitory effect on Botrytis cinerea,and reduced the gray mold of strawberry during storage.On this basis,this thesis further studied the mechanism of volatile metabolites of Hanseniaspora uvarum against Botrytis cinerea in vitro,and the effect on the expression of strawberry resistance genes during fumigation;In addition,the antagonistic effect and mechanism of trans-cinnamaldehyde,the volatile monomer of the yeast,on Botrytis cinerea in vitro had been investigated and we studied the inhibitory effect of trans-cinnamaldehyde on strawberry gray mold during storage and its specific mechanism.The specific research results were as follows:1.To study its inhibitory mechanism on Botrytis cinerea growth and effect on strawberry storage quality and resistance genes,the volatile metabolites of antagonistic yeast were used to fumigate Botrytis cinerea and strawberry respectively.From the results,it could be concluded that the antagonistic yeast volatiles had an inhibitory effect on the growth of Botrytis cinerea,and the mycelium inhibition rate gradually decreased with the increase of the culture time.Compared with the control,the expression of its pathogenic genes(NADPH oxidase:BcNoxA?BcNoxB?BcNoxD?BcNoxR?BcPls1?BcBem1:cell wall degradation enzymes:BcPg1?BcPg2?BcPme1?BcPlc1;toxic metabolites:BcP450?BcBoa6?BcBoa9?BcBot1?BcPksl4)changed,affecting its pathogenicity.Among them,the BcNoxB gene of NADPH oxidase was up-regulated,while the others were down-regulated.The expression of BcPlc1 gene in the cell wall degrading enzyme was down-regulated,while the others were up-regulated.The expression levels of virus-related genes were significantly increased.During fumigation,the expression levels of strawberry resistance-related genes FaCAT,FaSOD,FaPPO.FaAPX and FaPAL increased significantly;the volatiles could reduce the decay and deterioration of strawberry during storage,maintain color,slow down the decline of soluble solids and titratable acid,and maintain strawberry hardness to a certain extent.2.The inhibitory effect and mechanism of volatile monomer trans-cinnamaldehyde on the growth of Botrytis cinerea were studied in vitro.The results showed that transcinnamaldehyde significantly inhibited the mycelial growth of Botiytis cinerea and it had different effects on expression of the pathogenic genes:NADPH oxidase(BcNoxA,BcNoxB,BcNoxD,BcNoxR,BcPlsl and BcBeml),cell wall degradation enzymes(BcPg2,BcPme1 and BcPlc1),toxic metabolites(BcP450,BcBoa6,BcBoa9,BcBot1,and BcPks14).Different levels of up-or down-regulation occurred when compared with the control.Therefore,it was speculated that trans-cinnamaldehyde could affect pathogenicity by changing the expression of related pathogenic genes of Botrytis cinerea.3.The inhibitory effect of trans-cinnamaldehyde on strawberry gray mold under different concentrations(15.6 ?L/L,31.25?/L,62.5?L/L)and different fumigation time(1 d,2 d,and 3 d)was investigated.The results showed that different concentrations of transcinnamaldehyde had different inhibitory effects on strawberry gray mold,and also had different effects on strawberry color,hardness,soluble solids,and titratable acid.Among them,trans-cinnamaldehyde at 62.5 ?L/L had the best effect.Strawberries were fumigated by 62.5 ?L/L trans-cinnamaldehyde at 25? for 1 day,2 days,and 3 days,respectively.The lesion diameter of strawberry was the smallest when fumigated for 3 days.During fumigation,trans-cinnamaldehyde could improve the activities of CAT,PPO,APX and GLU,and delay the decline of SOD and PAL enzyme activities.The changes of expression of FaCAT,FaPPO and FaAPX genes were basically consistent with the enzymes activity.The expression of FaPAL gradually decreased during fumigation,and the gene expression of FaGLU showed an increasing trend in the late stage.4.Strawberry was fumigated with 62.5 ?L/L trans-cinnamaldehyde at 25? for 3 days?and then stored at 2(±1)? for 9 days.The effect of trans-cinnamaldehyde on strawberry gray mold during storage and its mechanism of inducing strawberry resistance and improving disease resistance were studied.According to the results,the lesion diameter of strawberry was significantly decreased after fumigation of trans-cinnamaldehyde.In terms of quality.trans-cinnamaldehyde could effectively maintain the color of strawberry,delay the reddening,slow down the change of soluble solids and titratable acids,while had little effect on the retention of hardness.Trans-cinnamaldehyde could induce resistance of strawberry,significantly increase the activities of CAT,PPO and APX,and delay the decline of SOD.For PAL and GLU,trans-cinnamaldehyde could delay the decline of enzyme activities to a certain extent.Enzyme activity was basically consistent with the corresponding gene expression trend except SOD.In addition,it also inhibited the increase of MDA content.In conclusion,the volatile compounds of Hanseniaspora uvarum could affect its growth and pathogenicity of Botrytis cinerea by inhibiting the expression of pathogenicity related genes in vitro,and induce strawberry disease resistance by improving resistance-related gene expression.The volatiles of the antagonistic yeast could also maintain the quality of strawberry during storage.Meanwhile,similar results were obtained in the study of the inhibitory effect of cinnamaldehyde on Botrytis cinerea in vitro.In addition,it was also found that trans-cinnamaldehyde could increase the activity of resistance-related enzymes and gene expression in strawberry,so as to reveal the inhibition mechanism of trans-cinnamaldehyde on gray mold of strawberry.It is expected that these results will provide theoretical support for further research on the inhibitory mechanism of volatiles of Hanseniaspora uvarum on strawberry gray mold.