Biological Control And Mechanisms Of Burkholderia Contaminans On Postharvest Gray Mold Of Strawberry

Strawberry fruit is attractive in color and rich in nutrition.It has been loved by people for many years because of its unique taste and rich nutritional value.At present,China's strawberry planting area reaches1.3 million mu,with an annual output of 1.3 million tons,ranking first in the world.However,strawberry is very vulnerable to rot and economic losses due to its soft tissue,strong respiratory function and extreme pressure resistance.In order to meet the market demand and reduce economic losses,strawberry preservation has become a hot topic.At present,the most effective measure to control strawberry postharvest diseases is low temperature storage combined with chemical fungicides.However,chemical agents can easily make pathogenic bacteria resistant,which has adverse effects on human health,environment and people's health.Therefore,biological control methods are sought to replace traditional chemical fungicides.Starting from the main diseases of strawberry fruits after harvest,the effects of B.contaminans B-1,an antagonistic bacterium,on strawberry storage and its inhibiting mechanism were studied.The preparation of fungicides and the induction of differentially expressed proteins in pulp were also discussed,which provided theoretical basis for a new biological preservation method of strawberry after harvest.The main results are as follows:(1)The main pathogens causing strawberry postharvest decay were Botrytis cinerea and Penicillium expansum by combining traditional morphological and molecular identification methods.(2)The inhibitory effect of Burkholderia contaminans B-1 on postharvest strawberry pathogen Botrytis cinerea in vitro was studied.The results showed that the antagonistic bacteria not only could effectively inhibit the mycelial growth of B.cinerea,but also had broad spectrum,and could inhibit other postharvest pathogens of fruits and vegetables.(3)The effects of pre-harvest spraying of Berkholderia contaminans B-1 on postharvest decay and fruit quality of strawberries were studied.It was found that pre-harvest spraying of antagonistic bacteria could not only effectively reduce the incidence of powdery mildew,but also promote the growth of strawberry plants.Compared with the control,the plant sprayed with biocontrol agent before harvest had better quality during storage after harvest.(4)The inhibition of antagonistic bacterium B.contaminans B-1 on postharvest diseases of strawberry fruits was studied.The results showed that the antagonistic bacteria could effectively inhibit the occurrenceof postharvest diseases of strawberry,whether natural rot or wound inoculation diseases,the inhibition effect was obvious.Chitosan and calcium chloride were selected from six cofactors which could effectively improve the antagonistic effect.It was proved that the inoculation mode of antagonistic bacteria first and then pathogenic bacteria was more conducive to disease control,which indicated that it was more important to prevent and control postharvest diseases of fruits.(5)The mechanism of antagonistic bacteria inhibiting fruit diseases was studied.Firstly,antagonistic bacteria treatment could lead to structural changes of Botrytis cinerea,which resulted in mycelial growth deformity,blurred subcellular structure and protoplast outflow.Moreover,antagonistic bacteria had strong colonization ability at fruit wounds and could compete with pathogenic bacteria in space and nutrition.Finally,antagonistic bacteria could induce fruit growth.Resistance is involved in the process of phenylpropane metabolism and reactive oxygen species metabolism of fruit disease resistance,and can also cause changes in the related substances of fruit disease resistance.(6)Carriers,auxiliaries and stabilizers of B.contaminans B-1 wettable powder were screened.The optimum formula of Burkholderia cepacia was 70% antagonistic fermentation broth,4% sodium carboxymethyl cellulose,LS4% detergent,PEG8000 5% and 100% diatomite.(7)Lable free non-labeled quantitative proteomics was used to screen differentially expressed proteins against gray mildew in strawberry pulp.The results showed that 568 differentially expressed proteins(FC=1.5)were screened in strawberry tissues,of which 189 were up-regulated and 379 were down-regulated.Bioinformatics analysis showed that differentially expressed proteins were mainly concentrated in binding proteins and catalysis.Active protein(catalytic activity),cell part,membrane,cellular process and metabolic process.It is speculated that the protein up-regulated significantly participates in amino acid metabolism and ribosome metabolism.