| China’s apple production ranks the first in the world,effectively driving the development of China’s agricultural economy.However,apples are often infected by pathogenic fungi during post-harvest storage,reducing their quality and commercial value.Aspergillus rot is one of the common post-harvest diseases of apples during long-term storage.Some studies showed that A.niger caused the most serious Aspergillus rot symptoms of several Aspergillus isolated from apple fruit.At present,the main control method is chemical fungicide treatment,but excessive use of chemical substances will bring many hazards to the environment and human health.Therefore,it is necessary to develop new green control methods to control fruit postharvest diseases.Antagonistic yeast is an environment-friendly biological control agent with great market potential and is expected to gradually replace chemical fungicides.In this study,the object of study was Sporidiobolus pararoseus CC-HS1,which was isolated from the fruit surface,to investigate its biocontrol effect on postharvest A.niger infection in apples,and to explore the main biocontrol mechanism through phenotypic and transcriptome techniques,laying a theoretical foundation for the application of yeast in apple practical biocontrol.In addition,by adding glycine to the culture medium to cultivate antagonistic yeast,the resistance to oxidative stress and biological control effect of the yeast CC-HS1 can be improved,which provides a new way to enhance the biocontrol effect of the yeast in apple.The main research conclusions are as below:(1)Through in vitro and in vivo antagonistic tests,it was found that yeast CC-HS1 had a good inhibitory effect on A.niger,and the greater the concentration of yeast,the more obvious the inhibitory effect was.When the concentration is 1×10~8cells/m L,the inhibition effect of mycelium growth diameter in vitro reached 70%,and the inhibition effect of apple lesion diameter and decay incidence in vivo reached88.7%and 90%,respectively.(2)The experiment on the effect of different inoculation times of yeast on apple biocontrol showed that the earlier the yeast inoculation time,the smaller lesion diameter of apple was,when yeast was inoculated 36 hours in advance,the inhibition effect of lesion diameter could reach 91.6%;In addition,after spraying yeast on postharvest apples for 30 days,the apple decay incidence decreased by 50%,and there was no significant adverse effect on their quality indicators,indicating that yeast CC-HS1 wouldn’t affect the postharvest apple storage quality.(3)Preliminary exploration of yeast antagonistic mechanism showed that:The yeast CC-HS1 can rapidly colonize in apple wounds,the count of yeast reached its maximum on the third day at 25°C and 4°C,increased by 15 and 7 times,respectively;The biofilm formation ability gradually increases within 72 hours to isolate the contact between A.niger and apple wounds,thereby inhibiting the proliferation of A.niger;When the yeast co-cultured with A.niger,β-1,3-glucanase activity significantly increased,the enzyme activity increased nearly three times during 24 h,which had a certain degradation effect on the mycelial cell wall of A.niger;The inhibited spores of A.niger co-cultured with yeast can regerminate when transferred to fresh culture medium without yeast cells,confirming that nutrition competition is an important antagonistic mechanism.(4)Transcriptome experiments indicated that:In the presence of antagonistic yeast CC-HS1,there were 1621 differential genes in A.niger,692 up-regulated genes,and 929 down-regulated genes.Among them,genes related to energy metabolism,amino acid metabolism,cell membrane and cell wall related component synthesis,and antioxidant activity were down-regulated,indicating that the normal growth of A.nigerr was inhibited.In addition,the stress pathway related genes such as MAPK were up-regulated in order to resist external environmental stimuli.What’s more,five differential genes involved in these pathways were selected for verification,and the acetyl-co A synthase encoding gene ACSA,β-glucosidase encoding gene BGLM,the sterol 24-C-methyltransferase encoding gene ERG6,and the catalase encoding gene CATA were all down-regulated,and the Cytochrome P450 encoding gene CYP7A1was up-regulated.Compared with transcriptome results,the expression times was slightly different,but the trend of change was the same.(5)When the yeast CC-HS1 was treated by glycine,the content of free radicals and MDA in yeast cells significantly decreased,the activities of antioxidant enzymes and glutathione content significantly increased under oxidative conditions;Moreover,the biological control activity of apple is enhanced,thereby enhancing its practical effectiveness. |
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