The Antagonist Of Marine Yeast In The Biocontrol Of Fruit Postharvest Diseases

Fruit rot caused by pathogenic bacteria seriously impede the development of fruit industry in China. Chemical germicides are common postharvest disease control methods. But the chemical germicides have some shortcomings, for example, they could lead to environmental pollution, endanger human health, be hard to degrade and so on. However, for biocide could protect the ecological environment, reduce pesticide residues of chemical germicides, and ensure human health in food, it can be used for disease prevention and treatment In recent years, the application of microorganisms in biological control has developed rapidly, it is considered to be the most promising methods to replace the chemical germicides. The living environment of marine yeast is low temperature or high concentrations of NaCl, so it may have some excellent properties such as good tolerance to low temperature and high osmotic stress. Once the marine yeast is applied in the postharvest biocontrol, it may have more advantages than other microorganisms which live on land. As a result, the yeast collected from the ocean may has a significant inhibitory effect on postharvest pathogens of fruits. Our work carried out mainly from the following aspects:1. Both in vitro and in vivo methods were used to screen the marine biocontrol yeast. 9 strains of yeasts labeled DG-1, SA-1, M-1, NH-1, NJB-1, ZZF, HZ-9, PA-1, W-1 were found to have obvious inhibitory effect on Botrytis cinerea in YPD medium. 7 strains of yeasts labeled DG-1,HZ-2,SA-1,NH-1,ZZF,HF-2,HH-3 were found to have obvious inhibitory effect on Monilinia fructicola (G. Wint.) Honey in YPD medium. The yeasts laeled DG-1,SA-1,ZZFand NH-1 have obvious inhibitory effect both on the M. fructicola and B. cinerea And the yeast which is labeled DG-1 had higher inhibitory effect than the yeast labeled DG-1,SA-1,NJB-1,and W-1in both the diameter of plaque and the morbidity.2. In the study, the morphological, physiological, biochemical and molecular methods were used to identify the yeast of DG-1. The cell and colony of the yeast labeled DG-1 were served for the experiment of fermentation of sugars and the only carbon source. Meanwhile, 18sRNA and ITS sequences were used to identify the phylogenetic relationship. From the Morphological, physiological , biochemical identification and molecular biological identification, the yeast of DG-1 was identified as Aureobasidium pullulans preliminaryly.3. In the inhibitory effect of A. pullulans on the peach fruit, the results showed that incidence of peach fruit was inversely proportional to the concentration of A. pullulans.At the same time, the fruit lesion diameter and morbidity were closely related to the concentration of A. pullulans .However, the inhibitory effect of A. pullulans on the spore germination of Botrytis cinerea was not obvious. A. pullulans could not completely inhibit the spore germination of B. cinerea. And the inhibitory effect of A. pullulans cultured on PDA was better than that cultured on YPD medium.4. In the study of A. pullulans'antibacterial mechanism, the cell suspension had the strongest inhibitory effect on B. cinerea, but the solution of heat treatment and the filtrate culture had no inhibitory effect. The result showed that there was no valid material existed in the filtrate of A. pullulans. It can be primeryly proved that the inhibition mechanism of A. pullulans belonged to the type of nutrition competition.5. The fermentation of A.pullulans under different salinity, pH, temperature and time conditions were researched respectively. The results showed that A.pullulans had strong tolerance to both acid and alkali, and it growed rapidly especially on the alkaline condition. The best growth conditions for A. pullulans was 0% salinity, 25℃, and 36 h after incubation .In this study, among the existed 61 strains of marine yeast, one strain which had significant inhibitory effect on the pathogenic bacteria was identified as A. pullulans, and it preliminaryly proved that the inhibition mechanism of A. pullulans belonged to the type of nutrition competition. The germination conditions were also optimized at the same time.