| Citrus fruits are one of the most important fruits, and highly popular in the world. As reported, postharvest diseases of citrus fruits during transportation and storage, caused by a variety of pathogens, result in serious economic losses every year. Currently, control of postharvest diseases of citrus is mainly carried out by the application of fungicides. However, frequent application of synthetic fungicides have led to the proliferation of fungicide-resistant strains and increasingly degenerated the effectiveness of these fungicides. Besides, a growing environmental contamination and human health problems caused by misapplication of fungicides on crops have raised global concerns. Therefore, it is necessary to develop safe and effective alternative methods for disease control of citrus fruits.Recently, biocontrol have been proved effective alternative measures for disease control of fruits and vegetables. Many antagonistic yeasts were reported to greatly inhibit postharvest disease of citrus. However, biocontrol efficacy of yeasts under semi-commercial conditions are often lower than synthetic fungicides. The objective of this study were to isolate effective yeast and enhance synergetic effect of antagonistic yeast combined with phosphatidylcholine on postharvest control of green mold of citrus.This study focused on following aspects:(1) isolation of effective antagonists;(2) the effect of Hanseniaspora uvarum and phosphatidylcholine on green mold of citrus caused by Penicillium digitatum;(3) possible defense mechanisms of induced disease resistance of citrus by the treatment of H. uvarum and phosphatidylcholine.The main research findings were summarized as follows:(1)in vitro and in vivo screening experiments indicated that, antagonistic yeasts labeled Y1, Y2, Y3 and Y4 all showed inhibitory effect to the pathogen Penicillium digitatum in citrus, Y3 was observed to show the best inhibitory effect. Experiments on DNA molecule sequencing, morphological characteristics analyses were conducted, the results identified Y1 as Issatchenkia hanoiensis strain, Y2 as Candida zemplinina strain, Y3 as Hanseniaspora uvarum strain and Y4 as Pichia manshurica strain. There was no report on the prevention of postharvest green mold of citrus fruits by using the yeast Hanseniaspora uvarum.(2)The results showed that H. uvarum at concentrations 1×106, 1×107, 1×108 and 1×109(cells/m L) significantly inhibited green mold of postharvest citrus compared to the control. The higher the concentration, the better and the efficacy was. Different concentrations of phosphatidylcholine significantly improved the efficacy of H. uvarum against postharvest green mold decay compared with control at 20°C. Especially, the combined treatment of phosphatidylcholine(1.5% w/v) with H. uvarum was the most effective treatment and reduced the green mold decay incidence and lesion diameter of fruits up to 93.5% and 5.6 mm, respectively. It was observed from the findings that, phosphatidylcholine(1.5% w/v) significantly improved the population dynamics of H. uvarum in citrus wounds at 20°C. H. uvarum treatment alone significantly reduced natural decay of postharvest citrus compared with the control. Phosphatidylcholine(1.5% w/v) enhanced the efficacy of H. uvarum in controlling natural decay of postharvest citrus. There were no significant influences with respect to storage quality parameters to citrus in three treatments. Weight loss of citrus treated with H. uvarum in combination with phosphatidylcholine(1.5% w/v) was significantly less than control treatment and H. uvarum treatment alone.(3)The possible mechanisms involved include: Improved the ability of antagonists to survive and proliferate in fruits wounds for better competition for nutrients and space with pathogens; inhibited spore germination and mycelial development of P. digitatum in wounds; induced the postharvest fungal diseases resistance by regulating the defense-related enzyme activity, active oxygen metabolism and antioxidant system in citrus peel. |
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