The Effect And Mechanism Of Antagonistic Yeast, Alone Or In Combination With Hot Air Treatment On The Reduction Of Postharvest Disease On Cherry Tomato Fruit

Cherry tomato is an important agricultural commodity and widely planted in China. Because many postharvest pathogens infect through wounds caused during harvest and are readily accessible to treatment with antagonists, biological control is considered a desirable alternative to chemical control. Furthermore, heat treatment is a non-damaging physical treatment that can be used to alleviate physiological diseases of various commodities. Therefore, in this paper, we will select cherry tomato fruit as experimental material, and our purpose is to research the effect and mechanism of antagonistic yeast (Pichia guilliermondii), alone or in combination with heat treatment (Hot air treatment,38℃) on the reduction of postharvest disease on cherry tomato fruit.The contents and results are as follows: 1. Biological control of the postharvest pathogens Botrytis cinerea, Alternaria solani and Rhizopus stolonifer on cherry tomato fruit by P. guilliermondiiIn mature green cherry tomato fruit, P. guilliermondii controlled three postharvest pathogens of tomato (B. cinerea, A. solani and R. stolonifer). Moreover, there was a close link between the concentration of the antagonistic yeast and the control effect. Cell suspensions at 108 CFU mL-1 were most effective in controlling all three tomato pathogens. P. guilliermondii showed efficacy against all three pathogens, but it appeared to be most effective against R. stolonifer.In tomato fruit at three different stages of maturity (red, pink, or mature green), a cell suspension of P. guilliermondii at 108 CFU mL-1 significantly decreased the rate of natural infection. Based on the results of an inoculation experiment, lower yeast concentrations (107 CFU mL-1) could effectively inhibit infections caused by all three pathogens, and it may be possible to use lower numbers of cells of the antagonistic yeast to control natural diseases. In this study, P. guilliermondii did not significantly affect fruit quality parameters such as FW loss, total soluble solids content, titratable acidity content, ascorbic acid content, and fruit colour of cherry tomato fruit during postharvest storage. 2. Mechanism of the yeast P. guilliermondii against postharvest pathogens on cherry tomato fruitThe yeast P. guilliermondii, was examined for its effects to control R. stolonifer on cherry tomato fruit during storage time, and in order to highlight the reason for biocontrol, possible mode of action was discussed. Results showed that the yeast autoclaved culture and culture filtrate had no effect in controlling postharvest disease caused by R. stolonifer, and inoculating P. guilliermondii prior to R. stolonifer had better biocontrol efficacy. Moreover, rapid colonization of the yeast on wound sites was observed during initial three days at 20℃, and then the population stabilized for the remaining four days. This phenomenon indicated that at room temperature, P. guilliermondii could acclimatize itself to the environment of tomato fruit wounds and occupy the living space quickly. All of the above results indicated that P. guilliermondii did not produce an antifungal substance, however, competition for nutrients and space on wounds appeared to play a role in the activity of biocontrol and it might be one of the mechanisms. In addition, the fruit inoculated with P. guilliermondii changed the expression of activities of peroxidase (POD), polyphenoloxidase (PPO), superoxide dismutase (SOD), catalase (CAT), phenylalanine ammonia-lyase (PAL), chitinase (CHI) andβ-1,3-glucanase, all of which were correlated with the onset of induced resistance. This result suggested that cherry tomato fruit was capable of responding to the yeast P. guilliermondii, which could activate defensive enzymes, thereby induced host disease resistance. This might be also one of the mechanisms.3. Effects of postharvest hot air treatment on quality parameters and decay development of cherry tomato fruitCompared to synthetic fungicides, biocontrol agent such as antagonistic yeast lacks eradicative ability, its spectrum of activity is narrower, and the effect of environmental factors is generally greater. It is therefore necessary to use an integrated strategy rather than a single approach. Heat treatment is a non-damaging physical treatment that can be used to alleviate physiological diseases of various commodities. The current study investigated the effects of heat treatment and antagonistic yeast, either alone or in combination, on the quality parameters and incidence of fungal infection in cherry tomato fruit.Hot air treatment (38℃) was used in this experiment and the results are as follows:(1) hot air treatment controlled three postharvest pathogens of tomato (B. cinerea, A. solani and R. stolonifer) effectively. Moreover, longer heat treatment gave a lower incidence of disease. Although cherry tomato fruit received hot air treatment (38℃) for only 24 h, the postharvest gray mold decay, black spot decay and Rhizopus decay were all significantly reduced. (2) hot air treatment (38℃for 24 h) did not significantly affect fruit quality parameters. However, hot air treatment (38℃for 48 h or 72 h) impaired the contents of total soluble solids, titratable acidity and ascorbic acid of cherry tomato fruit. Furthermore, hot air treatment (38℃for 72 h) made fruit color change fast. Therefore, considering all of the above results and the rule for saving energy and social capital, hot air treatment (38℃for 24 h) was selected in the following experiments.4. A combination of P. guilliermondii and hot air treatment prevents cherry tomato spoilage by fungiResults showed that antagonistic yeast P. guilliermondii’s ability to survive was inhibited gravely by the 38℃hot air treatment and this yeast was not heat-resistant, thus controlling postharvest diseases by applying P. guilliermondii after postharvest hot air treatment is recommended. In addition, for controlling various diseases, heat treatment or antagonistic yeast alone is not satisfactory; the best method, according to this research, is the combination of hot air treatment and P. guilliermondii, which has significant efficacy in controlling postharvest diseases of cherry tomato fruit caused by B. cinerea, A. solani and R. stolonifer.Scanning electron microscopy (SEM) observation indicated that hot air treatment at 38℃for 24 hours can inhibit hyphae growth and spore germination of R. stolonifer. Furthermore, P. guilliermondii multiplied rapidly on fruit wounds, and its cells had a strong capability of competing for nutrient substance and living space with pathogen. Although the combination of hot air treatment and P. guilliermondii not to eradicate pathogens existing on fruit wounds, the cells of yeast P. guilliermondii reproduced on fruit wounds and firmly attached to fungal hyphae, inhibiting their ability to infect cherry tomato fruit and competing for nutrients and living spaces to provide persistent protection. Furthermore, the result of electronic nose also showed that a combination of hot air treatment and P. guilliermondii is one of the most effective techniques at controlling postharvest fungal spoilage in cherry tomato fruit.5. Antagonistic yeast in combination with hot air treatment reduces diseases and elicits the active defense responses in harvested cherry tomato fruitIn recent years, considerable amount of research has focused on the active resistance in harvested fruits and vegetables, which acts as an important manageable form of crop protection. Results showed that hot air treatment at 38℃for 24 h in combination with P. guilliermondii at 108 CFU mL-1 was the most effective approach to reduce various infections on cherry tomato fruit’s wounds. Moreover, the combined hot air and P. guilliermondii treatment stimulated a rapid increase of H2O2 and higher lignin deposition in cherry tomato fruit showing that the oxidative burst and biological synthesis of lignin might play important roles in the fruit’s active defense responses. In addition, the reduction of the fruit’s susceptibility to pathogens by the combined treatment was positively correlated with higher activities of phenylalanine ammonia-lyase (PAL) andβ-1,3-glucanase in cherry tomato fruits, both of which are associated with plant defense responses.6. Effects of preharvest P. guilliermondii treatment on quality parameters and decay development of cherry tomato fruitMany pathogenic microorganisms have penetrated the fruit during the period of fruit growth, but the symptom of diseases usually be shown until fruit being stored with appropriate environmental conditions. In order to reduce the incidence of postharvest diseases, the primary prevention for such diseases should be taken to strengthen the field management before fruit harvest. Therefore, the purpose of this study was to evaluate the effects of preharvest P. guilliermondii treatment on quality parameters and decay development of cherry tomato fruit. Based on the results of this experiment, we suggested that:(1) both preharvest P. guilliermondii treatment and the spraying frequency did not significantly affect fruit quality parameters regardless cherry tomato fruit growing or stored after harvest. (2) preharvest P. guilliermondii treatment significantly reduced the incidence of postharvest natural decay, and the efficacy of biological control was positively correlated with the spraying frequency of P. guilliermondii. (3) preharvest P. guilliermondii treatment induced the defensive enzymes of cherry tomato fruit, such as POD, PAL andβ-1, 3-glucanase, which was related to host disease resistance. Furthermore, the efficacy of induction was positively correlated with the spraying frequency of P. guilliermondii. (4) the ability of P. guilliermondii to colonize on the surface of fruit was also positively correlated with the spraying frequency of antagonistic yeast.