The Antimicrobial Effect Of Metschnikowia Pulcherrimayeast On Anthracnose Of Postharvest Mango Fruits And The Related Mechanism

Mango(Mangifera indica L.)is one of the fruits widely cultivated in tropical and subtropical regions.Anthracnose caused by Colletotrichum gloeosporioides(Penz)is well known as one of the most destructive postharvest diseases in mango industry.The traditional method for controlling postharvest anthracnose in mangoes is to use chemical fungicides.Traditional chemical fungicides residuces on the fruits surface threaten human health and environmental safety.Biological control caters to China's national green development strategy.A variety of domestic and foreign studies demonstrated that the use of the antagonistic yeasts have been the effective ways to control of postharvest diseases of fruits and maintained storage quality of various fruits.In this paper,the effects of Metschnikowia pulcherrima(M.pulcherrima)isolated in our laboratory on controlling anthracnose and storage quality of mango fruit were investigated.The mechanisms of M.pulcherrima against C.gloeosporioides were also studied.The results are as follows:(1)The bacteriostasis effect of M.pulcherrima on C.gloeosporioides was studied in vitro.The results demonstrated that M.pulcherrima could inhibit the growth of C.gloeosporioides hyphae in the YPD medium.The wet weight of mycelial in the control group was 38.89 times that of the treated group,and dry weight of the mycelial of control group was 88.85 times that of the treated group on 5th day.The population dynamics of M.pulcherrima were measured at low and normal temperatures,the population peaks of M.pulcherrima appeared on day 5 at 15 ? but the peaks were appeared on day 3 at 25 ?.With the increase of yeast concentration,the inhibitory effects on anthracnose increased and then decreased,and its optimal concentration was 108 CFU/mL.(2)The inhibitory effect of M.pulcherrima on anthracnose was studied in vivo.The yeast and C.gloeosporioides were inoculated on the wounded mangoes,the inhibitory rates of yeast to C.gloeosporioides were 57.81%and 78.82%respectively when stored at 15 ? and 25 ? for 12 days.(3)After immersed in M.pulcherrima suspension of 108 CFU/mL,treated mangoes were benificial to maintain of the chroma b*values,fruit firmness,titratable acidity,vitamin C and soluble solids content compared with the control.(4)Competition for nutrients and space is one of the mechanisms of M.pulcherrima yeast against anthracnose.Competition for nutrients was detected based on the addition of the nutrients.It was observed that M.pulcherrima was able to compete for nutrients with C.gloeosporioides,and to assimilate carbohydrates rapidly,especially glucose.Competition for space was detected through the inoculation of pathogens and yeast in chronological order and different time spans.The earlier the yeast inoculated was,the smaller the lesion diameter was.(5)Competition for iron existed between M.pulcherrima and C.gloeosporioides,yeast inhibited the growth of C.gloeosporioides by consuming the iron elements in the environment.(6)M.pulcherrima could produce biofilm.It was observed that M.pulcherrima formed a biofilm on the mango surface under the scanning electron microscope.The biofilm did not begin to degrade after 72h,indicating that the biofilm maintained for a long time and would not degrade in a short time.(7)The results of experiments suggested that the activities of defence enzymes including phenylalanine ammonia-lyase(PAL),peroxidase(POD),chitinase(CHT)and?-1,3 glucanase(GLU)in mango fruits could be accelerated when only inoculated with the yeast,and anthracnose could induce the increase of defensive enzymes in mango fruit when only inoculated with the anthracnose pathogen.However,when the mango fruit was inoculated with yeasts and anthracnose pathogens at the same time,the defence-related enzyme activities were not superimposed.(8)It was found that M.pulcherrima could produce traces of nonvolatile antimicrobial substances in vivo and in vitro,but it was not enough to inhibit the growth of C.gloeosporioides.At the same time,M.pulcherrima could produce certain volatile antimicrobial substances,and the bacteriostasis rate reached 30.71%in vitro.GC-MS analysis showed that most of the volatile substances were alcohols,acids,esters,ketones,aldehydes and amides.(9)M.pulcherrima could produce extracellular chitinase and ?-1,3 glucanase,and the chitinase activity was higher in the presence of hyphal cell wall(CWP)and colloidal chitin,?-1,3 glucanase activity was higher in the presence of CWP and glucose.The PCR amplification on the DNA fragment of chitinase of M.pulcherrima showed that the product was about 500 bp.