Study On The Enhancement Of Antagonistic Yeast Stress Tolerance And Biocontrol Efficacy By Mannitol And Sorbitol

The objective of the present study was to determine the effect of sugar alcohol?mannitol or sorbitol?on the antioxidant response and subsequent stress tolerance and biocontrol efficacy of the antagonistic yeast,Debaryomyces hansenii.Which contains,the survival rate of antagonistic yeasts?D.hansenii?under different stress?oxidation,high temperature,salt?conditions was determined.Cell viability of pretreatment of mannitol or sorbitol to a subsequent exposure to high temperature,oxidative?H₂O₂?stresses,over a range of time.The effect of mannitol or sorbitol on induction of antioxidant enzymes,including catalase?CAT?,superoxide dismutase?SOD?in D.hansenii.The effect of mannitol or sorbitol treatment on antioxidant genes expression of D.hansenii using quantitative RT-PCR,and the yeast growth in apple wounds and in vitro at p H 4.0,yeast-peptone-dextrose?YPD?.The biocontrol efficacy of pretreatment cells of D.hansenii against blue mold and gray mold of apple.The research results show that,compared to the control yeast cells without pretreatment,the 0.1 M mannitol and 0.1 M sorbitol treatments improved the tolerance of D.hansenii to subsequent oxidative and high-temperature stress,pretreated yeast cells had a significantly higher cell survival.Treated cells also exhibited a lower accumulation of intracellular reactive oxygen species?ROS?,relative to non-treated,control yeast cells,when exposed to a subsequent oxidative?30 m M H₂O₂?or heat?40.5 ^oC?stress for 30 min.Pretreated yeast cells had a significantly higher enzyme activity?CAT and SOD?,and catalase and superoxide dismutase gene expression level,relative to non-treated,control yeast cells,when exposed to a subsequent oxidative?30 m M H₂O₂?or heat?40.5 ^oC?stress for 30 min.All D.hansenii multiply rapidly in fruit wounds and in vitro p H 4.0?YPD?.The population of Pretreated yeast cells was significantly higher than the population of untreated yeast cells at 1 to 4 days.The in vitro growth assay also indicated that pretreated yeast cells of D.hansenii grew more rapidly in YPD at p H 4.0?a p H value similar to Fuji apple flesh?in the initial 48 h.The antagonistic yeast,D.hansenii,significantly reduced both disease incidence and lesion diameter of both blue mold and grey mold of apple caused by P.expansum and B.cinerea,respectively.More important,lesion diameters caused by P.expansum and B.cinerea were significantly smaller on apple fruits inoculated with mannitol or sorbitol pretreated yeast cells,compared to untreated yeast cells.The incidence of the untreated yeast cells group was reduced by about 40%relative to the 100%disease incidence of the control group.At the same time,the incidence of mannitol or sorbitol pretreated yeast cell groups was reduced by about 60%.It can be seen that the biological control effect of D.hansenii is significant.More importantly,prereatment yeast cells exhibited a greater level of control efficacy than untreated yeast cells for both disease incidence and lesion diameter.