Inhibition Of 9 Common Volatile Organic Compounds On Spore Formation Of Penicillium Digitatum And Its Mechanism

In this experiment,the main pathogenic fungus of citrus postharvest-Penicillium digitatum was used as the tested strain,and 9 kinds of microbial volatile organic compounds were selected for the determination of mycelial growth,spore production and spore germination inhibition.The 9 commonly used chemical fungicides were used as controls to study the antibacterial activity of these 9 volatiles.Orthogonal test was used to screen out the most active ratio,and test its inhibition of green mold on citrus fruits and the incidence of natural storage to determine its effect on postharvest preservation and disease prevention of citrus.By observing the morphology of the conidiophore of P.digitatum after treatment with 9 volatiles and determining the expression of key spore-producing genes,the mechanism of inhibition of the sporulation of P.digitatum was determined.This research is of great significance to the research and development of green fresh-keeping bactericidal fumigants and the green control of citrus postharvest diseases.The main results of the study are as follows:(1)Among the nine selected volatiles,ethyl propionate,isobutanol,2-methyl-1-butanol and phenethyl alcohol have inhibitory effects on the growth of P.digitatum hyphae,with EC50 values of 1.816,0.272,0.154,3.923,respectively μL/cm3.Among them,ethyl butyrate,isobutanol and 2-methyl-1-butanol have the best inhibitory effects on P.digitatum sporulation,with EC50 values of 0.008,0.009,and 0.010 μL/cm3,respectively.Isobutanol,2-methylbutyl acetate and 2-methyl-1-butanol have the best activity in inhibiting the germination of P.digitatum spores.Nine kinds of volatiles have excellent inhibitory effects on the spore formation of P.digitatum.(2)A three-level orthogonal test was performed on nine volatiles.Among the 27 combination formulas,No.17 combination(ie ethyl propionate:isobutyric acid inhibition:2-methyl butyrate:ethyl butyrate:isobutanol:2-methylbutyl acetate:2-methyl-1-butanol:isobutyric acid:phenethyl alcohol=1:2:3:3:1:3:1:3:3)on the P.digitatum inhibitory activity of mycelium growth and sporulation of mold is the best.Among the traditional pesticides tested,Pyraclostrobin,Prochloraz and Fluazinam have the best activity against P.digitatum,with EC50 values of 0.005,0.019,and 0.035 mg/L,respectively.The conventional antistaling agent prochloraz has the best control effect on green mold,but it starts to develop on citrus on the 5th day after inoculation.On the other hand,the onset time of volatiles of mixed diatomite is one day later,and only white hyphae grow without spores.(3)The inhibitory effect of volatiles on P.digitatum may be related to the changes in the expression of key genes related to sporulation.The test results show that the treatment of ethyl butyrate will cause the expression of three key sporulation genes of P.digitatum(brlA,abaA,wetA)to be significantly increased,2-methylbutyl acetate,2-methyl-1-Butanol and isobutyric acid treatment resulted in a significant up-regulation of the three genes;low-level ethyl propionate treatment stimulated a significant up-regulation of the three genes,and high-level treatment resulted in a significant down-regulation;isobutanol treatment was just the opposite.The combination of 9 volatiles significantly resulted in a significant down-regulation of three genes.The regulation of volatiles on the expression of key sporulation genes resulted in poor development of P.digitatum conidiophore and spore-shaped spore-forming cells,thereby inhibiting P.digitatum sporulation.The above test results showed that:9 kinds of volatiles changed the expression of key genes of P.digitatum sporulation,causing the conidiophore to fail to develop normally,thereby inhibiting the production of spores of P.digitatum.It can effectively inhibit the spread of P.digitatum in postharvest citrus,and has good application prospects for postharvest storage and preservation of fruits.