| Blue and grey mold are primary postharvest diseases of apple fruits. Pathogens attacks are main cause of postharvest losses. Generally, synthetic fungicide was considered to be an effective means for controlling postharvest diseases. However, its disadvantages such as chemical residues in foods, environmental pollution, and the occurrence of fungicide-tolerant strains of pathogens, have accelerated the development of alternative approaches. Among these, biological control using harmless antagonistic microorganisms was proved to be a promising strategy for managing fruit diseases.The aim of this research is to isolate and screen effective antagonistic yeasts against blue and grey mold. The inhibition effects and their population dynamics in wounds were evaluated after the antagonistic yeasts AY-2 and F-5 were screened. Main conclusions were drawn as follows.1. There were 376 strains isolated from the surface epiphytes of apples and rhizosphere soil using the method of serial dilution. After primary and further screening in vitro, 12 strains exhibited inhibitory activity to Penicillium expansum and 11 strains exhibited inhibitory activity to Botrytis cinerea. Among screened strains, it was found that the isolates AY-2 was the most effective antagonists against P. expansum and F-5 was the best one against B. cinerea on apples through Fruits-inoculation test. The inhibition rate of isolates AY-2 got to 81.67% at 25℃.And the inhibition rate of isolates F-5 reached 83.33% at 25℃.2. The effects of antagonistic yeasts increased with the increase of antagonists cell population when the yeast at the concentrations of 10 -10 CFU/mL. Fruits were treated with antagonistic yeast suspension at 3 × 108 CFU/mL at various time intervals (48h, 24h, 4h, 0h) before and after challenge-inoculated with pathogenic spore suspension at 104 spores/mL. The efficacy of yeast against B. cinerea and P. expansum was maintained when it was applied simultaneously with or before the pathogens. However, the efficacy decreased when applied after the spores. The result of inoculation-time test showed that the efficacy of biocontrol increased significantly with the time antagonists applied before pathogen inoculated. In mixed-antagonists inoculation test, the blue mold infection rate was reduced to 8.33% when the two yeast AY-2 and 34-9 suspensions were applied simultaneously. This meant that the efficacy of the mixture excelled they applied individually and indicated significant discrepancy between them. The infection rate of grey mold was 15% when isolates AY-2 was mixed with F-5. And this rate was 13.33% when yeast 34-9 was mixed with F-5. It suggested that the efficacy of the two mixtures was better than that of F-5 and 34-9. In the antangonists-enhancement test, the resultshowed that CaCl2 elevated biocontrol efficacy of yeast AY-2. While the infection rate of blue mold was doubled than yeast AY-2 applied alone. And the infection rate of grey mold increased nearly 3 folds compared with yeast F-5 separate application when antagonists were combined with chitosan.3. Rapid colonization of isolates AY-2 and F-5 in wounds was observed whether pathogenic spores inoculated. The population of AY-2 increased 116.67 folds after 48h. When P. expansum spores inoculated simultaneously, the population increased 132.67 folds after 96h. The population of F-5 increased almost 200 folds after 72h. While it was 290.12 folds compared with the start point at 72h when B. cinerea spores co-inoculated.
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