Study On Effect And Mechanism Of Antagonistic Yeast In Combination With Hot Air Treatment On Postharvest Disease Of Strawberry

Strawberry is a highly economical and nutritional fruit with flavor, soft and juicy. However, due to the thin peel and high water content of strawberry fruit and mechanical wounds is easy to appear, which is infected by postharvest pathogen during storage and transportation. Gray mold decay is the major postharvest fungal disease of strawberry. In this paper,we select strawberry fruit (Fragaria X ananassa Duch. cv. Toyonoka) as experimental material, and the study is designed to research the effect and the possible mechanism of antagonistic yeast(Cryptococcus laurentii), alone or in combination with hot air treatment (38℃) on the reduction of major fungal disease of grey mold on strawberry. The results are as follows:1. A cell suspension of C. laurentii at108CFU ml-1significantly reduced grey mold decay and natural disease on strawberry fruit whether it is stored at room temperature or under refrigerated conditions. C.laurentii can reduce weight loss of strawberry fruit, but have no effect on the other storage quality. The results showed that C.laurentii did not secrete an antifungal substance and parasitism of pathogen. C.laurentii could inhibited postharvest disease on strawberry mainly through competing nutrition and living space with pathogens and inducing the activity of POD, PAL, SOD, CAT and (3-1,3-glucanase, and enhance the resistance. This may be one of the important mechanisms.2. Hot air treatment at38℃for24h effectively inhibited grey mold decay as well as natural decay and reduced the degree of the disease. However, prolonged heat treatment will accelerate fruit decay. Hot air treatment at38℃for12h or24h have no significantly affect on fruit quality parameters, but Hot air treatment at38℃for36h impaired the quality parameters. Furthermore hot air treatment38℃for36h will make the fruit color change fast. Therefore, we select hot air treatment at38℃for24h as heat treatment condition in the following experiments. The in vitro experiment showed that hot air treatment significantly inhibited spore germination and mycelial growth of B. cinerea. Also hot air treatment could induce the activity of PAL, POD and chitinase, promote the synthesization of the total polyphenol, and enhance the resistance to pathogen. Therefore these results indicate that hot air treatment can effectively control postharvest disease of strawberry possibly through indirectly inducing disease resistance and directly inhibiting pathogen growth.3. The combined treatment of hot air treatment (38℃,24h) and C. laurentii showed the lower incidence of grey mold decay and natural disease on strawberry than each treatment alone. The results showed that combined treatment reduce the weight loss, delay the hardness decrease under refrigerated conditions, but have no effect on other storage quality. The in vitro experiment showed that combined treatment has lower rate of spore germination and shorter length of germ tube of B.cinerea. Meanwhile, the combined treatment induced higher activities of the defense-related enzymes including PAL and β-1,3-glucanase, and accelerated composition of total phenolics in strawberry than each treatment alone to enhance the resistance. Thus, these results suggested that a combination of heat treatment and C. laurentii may be a useful technique to reduce postharvest disease in strawberry fruit.4. The results showed that the concentration of108CFU mL-1of yeast cell suspension spraying could effectively reduce strawberry fruit rot caused by Botrytis cinerea as well as natural disease, the more the number of preharvest spraying, the better the inhibitory efficacy. Antagonistic yeast before harvest spraying could reduce the weight loss rate, delay the hardness and ascorbic acid content decrease of strawberry fruit, but had no significant effect on the contents of soluble solids, titratable acidity, fruit surface color and aroma. Preharvest application with C.laurentii induce the defensive enzymes of strawberry, such as β-1,3-glucanase, POD and PAL. Meanwhile, the effect of induction was correlated with the spraying frequency of C.laurentii. Furthermore, the ability of C.laurentii to colonize on the epidermis of strawberry fruit was also correlated with the spraying frequency of yeast. Bengal agar plate and scanning electron microscopy test results showed that preharvest application with C.laurentii before harvest6d,3d and Od could improve its ability to colonize on the epidermis of fruit in the field and during storage.