Biological Control Of Postharvest Blue Mold Of Kiwifruit By Meyerozyma Caribbica And Its Formulation

China is the world’s largest producer of kiwifruit.However,kiwifruit belongs to berries,its flesh is soft and tender,and it is easy to be infected by pathogen during storage and transportation,resulting in rot.Especially Penicillium expansum,which not only severely damaged the nutritional value and food safety of fruit,but also caused major economic losses to China’s fruit trade.At present,the main control methods for postharvest diseases of fruits are physical and chemical methods.Physical methods have high costs and are easy to affect the sensory quality of fruits,while chemical methods also have certain hidden dangers to human health and natural environment.In recent years,biological control has become a new method for controlling fruit postharvest diseases due to its safety,environmental protection,and effectiveness,and have become a research hotspot in the field of fruit postharvest disease control.In this paper,an antagonistic yeast,Meyerozyma caribbica,which can effectively control postharvest blue mold of kiwifruit,was isolated and purified from the surface of healthy kiwifruit.The physiological mechanism of M.caribbica’s biocontrol effect was explored,and the molecular mechanism of M.caribbica inducing resistance of kiwifruit to pathogen infection was reavealed.Finally M.caribbica was formulated with appropriate protective agent by freeze-drying technology which is expected to provide a theoretical basis for the commercial application of antagonistic yeast.The main research results of this paper are as follows.1.An antagonistic yeast M.caribbica was isolated from the surface of the healthy kiwifruit and verified the effect of controlling blud mold of kiwifruit with the known biocontrol yeast of my laboratory to prove M.caribibica has the best effect.The acute oral toxicity test showed that the yeast was actually safe and non-toxic.2.By exploring the biological control of blue mold of kiwifruit after harvest at different concentrations of M.caribibica and 1×10⁸ cells/m L was the optimal concentration to use.At the same time,after 26 days of spraying M.caribibica,the decay rate of kiwifruit decreased significantly,and the quality did not change apparently.3.The physiological mechanism of M.caribibica in controlling postharvest blue mold of kiwifruit mainly includes:（1）M.caribibica can significantly inhibit the growth of P.expansum on solid medium also obviously inhibit the spores germination of P.expansum in liquid medium and shorten the length of germ tube of the pathogen;（2）The volatile gas produced by M.caribibica can reduce colony diameter of P.expansum on solid medium;（3）M.caribibica has moderate ability of biofilm formation in vitro;（4）M.caribibica can rapidly colonize and grow stably on the surfaces and in the wounds of kiwifruit at 4℃and 20℃;（5）M.caribibica can increase defense enzyme（PPO,PAL,GLU）activities and the content of secondary metabolites（lignin,total phenols,flavonoids）in kiwifruit;（6）M.caribibica can improve the scavenging capacity of reactive oxygen species in kiwifruit,including improving antioxidant related enzyme（POD,SOD,APX）activities,and reduce the content of malondialdehyde（MDA）and the rate of superoxide anion(O^2-)production.4.The differentially expressed genes in kiwifruit of M.caribibica treatment group and control group were investigated by transcriptomics technology based on high-throughput sequencing and bioinformatics analysis and we found that many genes encoding different defense-related pathways（pathway of flavonoid biosynthesis,pathway of glycolysis/gluconeogenesis,pathway of plant-pathogen interaction,pathway of glutathione metabolism and pathway of phenylpropanoid biosynthesis）were identified by M.caribibica inducing expression to activate the pathway.At the same time,some key differentially expressed genes that may be related to the resistance of kiwifruit to blue mold was classified and selected（related to plant stress and disease resistance,related to improving plant antioxidant capacity,related to plant material transportation,related to plant signal transduction,related to improving plant cell wall strength and synthesis,and related to plant resistance material synthesis）5.Through response surface analysis,the optimal combination scheme of freeze-drying protective agent of M.caribibica was designed:11.59 g/100 m L skimmed milk powder,14.57 g/100 m L trehalose,2.74 g/100 m L L-sodium glutamate and 3.42 g/100 m L yeast extract.The results showed that the freeze-dried formulation of M.caribibica preparation can maintain a high survival rate and biological control effect on blue mold of kiwifruit during a long storage period.