The Study Of Control And Mechanism Of Action On Postharvest Diseases Of Fruit And Vegetables By Essential Oils

Considerable postharvest losses of fruit and vegetables are brought about by decay caused by fungal plant pathogens. Chemical synthetic fungicides are the primary means of controlling postharvest diseases. The side-effects of synthetic fungicides such as leaving high residues, high and acute toxicity, long degradation period, environmental pollution, in addition to causing the appearance of fungicide-resistant populations of storage pathogens mean that alternative effective, safety, eco-friendly strategies need to be developed for reducing losses due to postharvest decay pose negligible risk to human health and environment. The particular interest has focused on the potential applications of essential oils that have low mammalian toxicity, a broad spectrum of antifungal properties and eco-friendly properties as alternative chemical control measures. But there are no systematic studies about these essential oils to control the phytopathogenic fungi especially in vivo. The studies of these essential oils to control postharvest diseases and the antifungal mechanism will be helpful for the practical application of essential oils.According to the experiment design, the fumigant toxicity and contact antifungal activity of five essential oils (thyme oil, sage oil, nutmeg oil, eucaptus oil and cassia oil) against eight phytopathogenic fungi (Aspergillus nige, Alternaria alternata, Penicillium citrinum, Penicillium expansiun, Penicillium dititatum, Penicillium italicum, Botrytis cinerea and Pestalotia sp.) was tested at different concentrations in vitro. Thyme oil and cassia oil had strong fumigant toxicity and contact antifungal activity against some phytopathogenic fungi. The fumigant toxicity and contact antifungal activity of the two essential oils in vivo, the effect of the two essential oils in combination with other control means on postharvest disease of cherry tomatoes were studied. Meanwhile, the antifungal mechanisms of essential oils were studies.The results were shown as below:1. Thyme oil had strong fumigant toxicity followed by cassia oil. Nutmeg oil exhibited a moderate action while sage oil and eucaptus oil presented weak fumigant toxicity to all pathogens. Thyme oil and cassia oil exhibited strong contact antifungal activities against the tested fungi. Nutmeg oil exhibited a moderate contact action while sage oil and eucaptus oil presented nocontact antifungal activity to all pathogens.2. Thyme oil as a fumigant showed a significant inhibitory effect against Alt. alternata on cherry tomatoes. Thyme oil and cassia oil reduced the percentage of decayed cherry tomatoes, jujubes, grapes, sweet orange and cherry caused by fungal pathogens. But thyme oil and cassia oil showed no inhibitory effect on the decay of peach, apple, pear, cumquat, and orange.3. The antifungal effect of cassia oil and thyme oil against Alt. alternata was enhanced significantly by combining with KG, NaCl, MgSC"4 and CaC^ in vitro and in vivo. The combination of thyme oil and CMC or phenolic acids or chitosan may enhance antifungal effect of thyme oil in vivo. Cassia oil with phenolic acids could show a significant inhibitory effect against Alt. alternata on cherry tomatoes. The inhibitory effect of cassia oil against Alt. alternata on cherry tomatoes was good when inoculated pathogen before treated with 500 uL/L cassia oil and hot air.4. The antifungal effect of cassia oil and thyme oil against Alt. Alternata were affected by the conditions in vitro and in vivo. The antifungal effect of 200 \iLIL cassia oil at pH 5 was best in vitro. Tween-20 and tween-80 weakened the antifungal effect of 200 uL/L cassia oil in vitro. Emulsifier op enhanced the antifungal effect of 200 uL/L cassia oil in vitro. The storage times and storage temperature had no effects on the antifungal effect of cassia oil in vitro and in vivo. The storage times had no effects on the antifungal effect of thyme oil in vitro and in vivo. But the proper temperature treatments would enhance the antifungal effect of thyme oil in vitro and in vivo. The inhibitory effect of 500 uL/L thyme oil against Alt. alternata in vivo was best after thyme oil was treated for one hour at 60°C in a water bath. The inhibitory effect of cassia oil and thyme oil at pH 5 against Alt. alternata of cherry tomatoes was best in vivo. Tween-20, tween-80 and emulsifier op weakened the antifungal effect of 500 (iL/L cassia oil and thyme oil in vivo. The treatment of adding 500 \iL/L cassia oil after inoculating pathogen could reduced the percentage of decayed cherry tomatoes effectively.5. Cassia oil and thyme oil alone or combined with other treatments significantly reduced the natural development of decay of cherry tomatoes. The quality parameters of cherry tomatoes treated with these treatments were similar to those of control cherry tomatoes, which suggested that these treatments did not impair quality parameters of cherry tomatoes.6. The main components of thyme oil and cassia oil were benzene, l-methyl-2-(l-methylethyl-, thymol, and cinnamaldehyde, respectively. These components were relative to the antifungal activity of these essential oils. The antifungally activities of cassia oil and thyme oil against Alt. Altemata were dependent on the concentration and exposure time. Spore germination assay demonstrated the inhibitory effect of cassia oil alone or in combination with salts against the spores of Alt. altemata. Cassia oil and thyme oil above 1000 uL/L showed significant lethal effect to the spores of Alt. alternata. Cassia oil affected the growth of hyphae of Alt. alternata. Cassia oil damaged the structures of cell membrane of hyphae and rendered them more permeable.In conclusion, the results indicated that cassia oil and thyme oil have good antifungal effect against Alt. alternata in vitro and in vivo. As long as the conditions and means of treatments were proper, cassia oil and thyme oil could reduce the percentage of some decayed fruit and vegetables. So essential oils can be used as a potential source of sustainable eco-friendly botanical fungicides, after successful completion of wide range trials.