| As a worldwide vegetable crop, tomato (Solanum lycopersicum) is one of the main vegetables in China. In recent years, tomatoes were continuous monocropped, driven by economic interests and limiting production cultivation conditions, hence causing serious continuous cropping obstacle. Continuous monocropping decreased tomato growth, and increased soil-borne disease, affecting tomato yield and quality. Thus, it is vital to overcome continuous cropping obstacles in tomato sustainable production. Previous studies showed that with the allelopathy, potato onion as a companion plant could increase tomato growth and alleviate tomato Fusarium wilt, caused by Fusarium oxysporum. However, the mechanisms of how allelochemicals were released from potato onion are not yet been proven.In this study, tomato and onion were as experimental materials. Pots experiments were conducted to explore the effects of allelochemicals from potato onion root exudates, natural evaporation and shoot leaching on tomato growth and physiology, for the purpose of finding the main pathway from which the allelochemicals were released. The potential allelopathy of volatile matter from different parts of potato onion on tomato growth and tomato Fusarium wilt were evaluated. The flavones in potato onion in bulbs were extracted using ultrasound and macroporous adsorption, and the effects of the flavones on F. oxysporum were examined. GC-MS was employed to isolate and identify the main substances in volatile matter from different parts of potato onion. Furthermore, ultraviolet spectroscopy (UV), infrared spectroscopy (IR), high performance liquid chromatography (HPLC) were employed to identify the structures of the flavonoid compounds, hence determine the main substance. This study would reveal the mechanisms in which companion cropping with potato onion could promote tomato growth and alleviate tomato Fusarium Wilt, and provide theoretical basis and technical support to associated studies.Main results of this paper were as flowing:1. Pots experiments showed that the potential allelochemicals were released from root exudates, volatilization and leaching from potato onion. The potential allelochemicals acquired by the three pathway could promote tomato growth at a low concentration, but inhibit at a high concentration, suggesting the double effects of the potential allelochemicals. At a concentration of 40 plants/plate in root exudates,80 plants/1.77m3 in volatiles and 0.02g/mL treatment in leaf extracts, the potential allelochemicals promoted tomato growth, increased activities of POD, CAT and SOD, increased proline content, and decreased electrical conductivity and MDA content.2. The volatiles from different parts of potato onion had inhibitory effects on tomato seedlings growth, and it was concentration dependent. The volatiles from potato onion leaves and root dry matter significantly inhibited F. oxysporum growth, and it was most inhibiting when the concentration of volatiles from leaves was at 0.03g/mL, with the inhibitory rate of 75.76%.3. The extraction methods for total flavonoids of potato onion were examined and optimized by single factor experiment and response surface analysis. The extraction process with the method of ultrasonic assisted extraction (UAE) was:ultrasonic for 25 min, ultrasonic power 345 W, extraction temperature at 60, liquid material ratio of 30 mL/g. The product rate of total flavonoids was 2.286% under this condition. The extraction process of reflux extraction (RE) was:extraction for 90min, extraction temperature at 70, ethanol concentration 65%, solid-liquid ratio of 30 mL/g, under this condition. The product rate of total flavonoids was 2.323%. The extraction efficiency in terms of product rate of total flavonoids between UAE and RE was similar, but it was less time and low temperature with the method of UAE, compared to RE, so UAE method was determine to extraction total flavonoids from potato onion in this study.4. Single factor experiment was used to optimize the purification process of total flavonoids from potato onion. The results showed that AB-8 macroporous resin was better for purification, and the process was as follows:the concentration and pH of sample was 0.558mg/mLand 4, respectively, and flowed through macroporous resin column with speed of 2BV/h. Followed by static adsorption for 30min, and then the sample was eluted using 3BV 70% ethanol solution with speed of 1BV/h. After this purification process, the purity increased from 17.43% to 52.56%.5. The total flavonoids abotained from potato onion had inhibiting effects on F. oxysporum, in terms of spore germination, sporulation, growth and biomass amount of mycelium. and the inhibition increased with the increase of concentration. The total flavonoids completely inhibited F. oxysporum mycelia growth at the concentration of 20mg/mL. After treatment with total flavonoids from potato onion, the relative conductivity and MDA content was higher than those of control. SOD and CAT activity increased at the beginning and then decreased, and were both lower than those of control after treatment for 72h.6. The chemical constituents of the volatile compounds from different parts of potato by GC-MS analysis. The results showed sulfur compounds were main ingredient, anddibutyl phthalate〠dipropyl disulfide and 2-ethyl-3-methyl tetrahydrothiophene were all detected in roots, stems and leaves of potato onion. Importantly, dibutyl phthalate and dipropyl disulfide have been proved to be allelochemicals.7. The structures of main active ingredients in total flavonoids from potato onion were analyzed by By UV, IR and HPLC analysis. The results suggested the main active ingredients are quercetin and kaempferol, which are both flavonol compounds... |
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