Isolation And Screening Of Antagonistic Yeast Strains And Control Effects On Postharvest Of Apples And Peppers

In order to prevent and control postharvest diseases of fruits and vegetables safely and effectively,30 yeast strains have been isolated from the leaves and fruits in three orchards in Tai'an.The purpose of this study was to screen out the yeast strains with antagonism against Botryosphaeria berengeriana,Penicillium expansum,Botrytis cinerea and Colletotrichum gloeosporioides.Testing effect of selected yeast strains H3,T2,T3,Z8 and their different treatment solutions on growth of fungal pathogens,and inhibitory effect of different concentration of yeast strains on 4 fungal pathogens and postharvest diseases,and growth and colonization of yeast strains on apple and peper fruits have been carried out,respectively.The effect of different elicitors on growth of yeast strains and fungal pathogens has been examined,respectively.Finally,4 yeast strains have been identified by morphological characteristic and molecular biology.The major results of this study are as follows:1.Results of inhibition activity in vitro and disease prevention effects in vivo showed that yeast strains H3,T2,T3 and Z8 had strong inhibition against pathogen of apple fruit ring rot,and their inhibition rates were 91.46%,91.06%,77.20%and 88.66%,respectively.After inoculation with 1×10⁸ cfu/mL yeast for 7 d,the disease control effect was 65.09%,82.54%,69.84%and 84.13%,respectively.Yeast strains H3,T3 and Z8 had strong antagonism against pathogen of apple gray mould,and their inhibition rates have reached 66.32%,61.26%and62.07%,respectively.After inoculation with 1×10⁸ cfu/mL yeast for 7 d,the disease control effect has reached 52.63%,47.37%and 63.15%,respectively.The yeast strain T3 produced an obvious inhibitory zone on the activity test plate of Penicillium expansum.After inoculation with 1×10⁸ cfu/mL yeast for 7 d,the disease control effect has reached 43.75%.Yeast strains H3,T2,T3 and Z8 had strong antagonism against pathogen of peper anthracnose,and their inhibition rates have reached 52.84%,88.76%,60.60%and 49.00%,respectively.After inoculation with 1×10⁸ cfu/mL yeast for 7 d,the disease control effect has reached 68.00%,60.00%,68.00%and 64.00%,respectively.2.Results of effect of elicitor on the growth of yeast and fungal pathogens showed that NaHCO₃ had the greatest influence on the growth of four yeast strains.The greater the concentration was,the more growth of yeast cells was inhibited.When the concentration of NaHCO₃ reached 4%and 2%,yeast was not able to grow.CaCl₂ had no effect on the growth of yeast cells.Chitosan had not influenced the growth of T3,Z8 and T2,but inhibited the growth of yeast strain H3.The higher the concentration was,the slower the growth of yeast cells,but the inhibition of NaHCO₃ was strong.Three different concentrations of different elicitors inhibited the growth of fungal pathogens.The expansion diameter of the mycelium treated with the elicitor was less than that of the control,in which the inhibition of NaHCO₃was the strongest.4%NaHCO₃ could completely inhibit the growth of four fungal pathogens.With the decrease of concentration,the inhibitory effect was weakened.3.Results of effects of different concentration and treatment solutions of yeast on growth of four fungal pathogens and their control effect showed that the higher yeast concentration,the better disease control effect when the yeast concentration was 1×10⁴¹×10⁸ cfu/m L.The inhibitory effect of yeast culture solution and yeast cell suspension on fungal pathogens was strong,and the average diameter of colonies was less than 4 cm.But the supernatant and the solution treated with high temperature did not inhibit the growth of the fungal pathogens.4.Results of determination of the growth dynamics of yeasts showed that the concentration of 4 yeast strains increased exponentially in YPD medium.The peak value occured at 24 h in YPD medium,and at 48-72 h on fruit wound.4 yeast strains were able to colonize rapidly in apple and pepper fruit,and yeast can steadily colonize fruit wounds.5.Results of effect of yeast on the mycoparasitism and the growth of mycelia of the pathogen showed that only strain T3 had mycoparasitism on the hypha of apple fruit ring rot under microscopic observation.In the co-culture experiment of yeast and pathogen mycelium,the inhibition rate of mycelia growth by yeast was over 90%.6.Identification of antagonistic yeast.According to the sequence alignment and phylogenetic tree analysis of specific DNA fragments and morphological characteristics.H3,T2,T3 and Z8 were preliminarily identified as Meyerozyma guilliermondii.