| As an essential nutritional source,fresh fruits play an important role in people’s daily life.However,postharvest decay caused by pathogenic fungi results in significant economic losses of stored fruits.Synthetic chemical fungicides are still the main method used to control postharvest decay over the past years.Concerns on health issues,ecological environment and food safety issue have made the continued use of chemical fungicides a serious consideration The utilization of wild species and strains of antagonists is recognized as one of the promising alternatives for the management of postharvest diseases in a variety of fruits.In this project,the objective was to evaluate a new yeast-based biocontrol system in morphology transition(yeast-like single cell to biofilm forms)of the antagonistic yeast,C.diversa.The conditions of biofilm formation in biocontrol yeast were figured out.Compared with the single-cell form,the tolerance to heat or oxidative stress and the biocontrol efficacy against gray mold was evaluated on apple and kiwifruit in biofilm forms of C.diversa.In order to gain more biomass of C.diversa to manage postharvest diseases on pre-and post-harvest in practical agriculral application,the study also investigated the effects of three key metal ions(Mg2+、Fe2+、Zn2+)on effective biomass and survival in yeast fermentation by using of experimental design method.Effective biomass,survival,antioxidant enzyme activity,levels of protein and lipid damage under the different initial concentration of metal ion were observed in C.diversa.The main findings are as follows:(1)When C.diversa was cultured on 2% agar YPD,the cells exhibited a single-cell morphology.In contrast,when a colony was transferred to 0.3% agar YPD,the yeast cells transitioned to a pseudohyphal morphology.(2)Compared with single-cell morphology,the biofilm form had higher tolerance to heat and oxidative stresses and greater biocontrol efficacy against gray mold on apple and kiwifruit than the yeast-like form.(3)Single factor experiments were utilized to determine the optimal range of three factors of Mg2+,Fe2+ and Zn2+ for the yeast biomass.Using the developed model,the maximum effective biomass of 5.28 g/L was obtained when Mg2+,Fe2+ and Zn2+concentrations were 1511.13,2.16 and 26.77 mg/L,respectively.(4)Different initial metal ion concentrations of fermentation conditions have significant effects on viability,biomass and physiological or biochemical characteristicsby C.diversa.The treatment Best(concentration of Mg2+,Fe2+ and Zn2+ by experimental design method in yeast fermentation)had higher biomass,viability and greater biocontrol efficacy than treatment Lack(Lack of Mg2+,Fe2+ and Zn2+ in in yeast fermentation)and MM(Minimum mineral in in yeast fermentation).Lower levels of protein and lipid damage under better fermentation conditions of response surface were observed in the Treatment Best and may be due to the activation of higher antioxidant enzyme activity.These optimized conditions significantly improved stress tolerance and biocontrol efficacy of C.diversa.In this study,the antagonistic yeast,C.diversa,reversibly shifted from a single-cell morphology on yeast peptone dextrose(YPD)medium with 2% agar to a pseudohyphal morphology on YPD with 0.3% agar.The tolerance of the pseudohyphal form to heat and oxidative stresses,as well as the biocontrol efficacy against Botrytis cinerea on apple and kiwifruit,was significantly higher as compared to the single-cell form.Mg2+,Fe2+ and Zn2+ were effective for accumulating effective biomass production,improving the activity of SOD and GSH-PX and inhibiting the accumulation rate of lipid peroxidation and protein carbonylation in C.diversa.These results provide new information on the impact of the morphology shift on stress tolerance or biocontrol performance and effective biomass accumulation by metal iron in biocontrol yeast C.diversa.It is essential for the potential application and development of biocontrol agents. |
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