Postharvest Biological Control Of Fruits And Vegetables By Marine Yeast Rhodosporidium Paludigenum

Considerable amount of fruits and vegetables is lost due.to decay after harvest.Microbial biocontroi agents have shown great potential as an alternative to synthetic fungicides for the control of postharvest decay of fruits and vegetables.Unfortunately,at present,the effectiveness and stability of yeast antagonists have not been reached a sufficient control level Wben compared with the synthetic fungicides.Meanwhile,although screening of large numbers of organisms has been reported, a serious shortcoming of biological control as currently tested and studied is that too few strains are examined.Thus,there is an increasing need for isolation of yeasts from new source,selection,testing of the yeast on the surfaces of fruits and studying the biocontrol mechanism of the yeast.According to the experiment design,one of the marine yeasts isolated from the south of East China Sea was identified as Rhodosporidium paludigenum Fell & Tallman(1984),which showed great biocontrol efficiency in inhibiting postharvest diseases of fruits and vegetables.The capability of growth of R.paludigenum,the separation and dryness methods,the safety of R.paludigenum,the efficacy of R.paludigenum alone or in combination with Other control means for controlling postharvest disease of cherry tomatoes,Chinese jujubes,oranges,pears,apples and persimmons were tested.Meanwhile,the efficacy of R.paludigenum for reducing natural decay development and quality parameters and the middle model application experiments was done.In addition,the mechanisms of R.paludigenum were studies.The results were shown as below:1.One of the marine yeasts isolated from the south of East China Sea was identified as Rhodosporidium paludigenum Fell & Tallman by CABI Bioscience Identification Services,which was shown great biocontrol efficiency in inhibiting the black and gray rots of cherry tomato.2.On the salt endurance and growth curve test,the marine yeast R.paludigenum showed more tolerance to osmotical stress than Rhodotorula glutinis or Cryptococcus laurentii in the nutrient yeast dextrose broth(NYDB).R.paludigenum stoped growing in the liquid medium(NYDB) added sodium chloride up to 16%(w/v),whereas R.glutinis or C.laurentii could not grow in the presence of sodium chloride over 12%(w/v).3.On the safety test,the results of acute toxicity to mice(food standard) showed the dried powder ofR.paludigenum is safe.4.On the test of manipulation of formulations,the activity of R.paludigenum was affected by the skim milk.The better protection from freeze-drying injury to R.paludigenum was provided by 10%skim milk.5.R.paludigenum showed great biocontrol activity in reducing the development of postharvest diseases of fruits and vegetables,including:black rot of cherry tomato and Chinese jujube,caused by Alternaria alternata;gray mold decay of cherry tomato,pear and apple;caused by Botrytis cinerea; green mold of orange caused by and Penicillium digitatum and Penicillium expansum;postharvest rot .of persimmon caused by Pestalotis diospyri.The concentrations of R.paludigenum had significant effects on biocontrol effectiveness to postharvest diseases of fruits:the higher the concentrations of R. paludigenum,the better the control efficacy.6.The main mode of action of R.paludigenum is competitive for nutrients and space.R. paludigenum rapidly colonized fruits wounds at ambient temperature so as to control pathogens of fruits.R.paludigenum induced the production of resistance enzymes of fruits,including polyphenol oxidase(PP0) and peroxidase(POD).Enhancing the resistance activity of fruits to pathogens may be another mechanism of control postharvest disease of fruits and vegetables of R.paludigenum.7.The efficacy of R.paludigenum on the control of postharvest decay of cherry tomato,Chinese jujube and.pear was enhanced significantly by combining with metal salts(NaCl and CaCl₂),food additives(carbonate,CMC-Na and sodium paraben) in vivo test.Meanwhile,the combination of 1x10⁷ cells/mL R.paludigenum and low doses of pesticide(0.1mg/g pyrimethanil) may enhance the inhibition of gray mold of cherry tomato.The efficacy of R.paludigenum for control of black mold of cherry tomato was improved when combined with heat treatment.Moreover,1x10⁷cells/mL R. paludigenum in combination with SBP and heat treatment showed great inhibition against of black rot of cherry tomato caused by A.alternata.8.R.paludigenum alone or in combination with CaCl₂,CMC-Na and sodium paraben significantly reduced the natural development of decay of cherry tomato,Chinese jujube and citrus, which suggested that R.paludigenum could be an alternative to chemicals for control of postharvest rots on these fruits.The quality parameters of fruits treated with R.paludigenum alone or in combination with CaCl₂,CMC-Na and sodium paraben were similar to those of control fruit,which suggested that R.paludigenum did not impair quality parameters of fruits.9.On pilot-scale experiment tests,R.paiudigenum had great biocontrol activity against gray mold and black mold of cherry tomatoes,1x10⁸ cells/mL R.paludigenum in combinationwith 2% CaCl₂ or 1x10⁷ cells/mL R.paludigenum in combination with low doses pesticide(0.1mg/g pyrimethanil) showed great biocontrol activity,which showed the great potential of R.paludigenum to control the postharvest decay of fruits and vegetables.