| Eggplant is widely cultivated in China. With the development of protected production, continuous cropping obstacle problem is increasingly serious, leading to poor plant growth, disease severity and significant reduction of production, has seriously affected the sustainable and healthy development of eggplant produciton. Continuous cropping obstacle is composed of soil borne disease, nutritional imbalance and allelopathy, the role of soil spread diseases is the key of the research. With the deepening of the research, people realize the close relationship between allelopathy and continuous cropping obstacles, and the toxic effect of allelopathy is one of the leading causes of eggplant continuous cropping obstacle, especially the toxic effect of root secretion. Many allelochemicals including cinnamic acid, vanillin and benzoic acid are detected in eggplant root secretion, cinnamic acid and vanillin are main allelochemicals. The release and accumulation of eggplant root secretion induce toxic effect, increase soil borne disease, cause the changes in the soil. Eggplant root secretion of allelopathy affects the plant itself and rhizosphere microorganisms, and the changes are related to the occurrence and development of continuous cropping obstacle. The research of root secretion has become a key of the continuous cropping obstacle.According to two main allelochemicals, vanillin and cinnamic acid, allelopathic effects of eggplant root secretion and grafting regulation mechanism were studied, in order to make sure the relationship between root secretion and continuous cropping obstacles, reveal the harmful and beneficial effects of grafting on allelopathy, clarify the mechanism of grafting on the stress relief and prevent the continuous cropping obstacle. This study has important theoretical and practical significance to eggplant production and promoting agricultural sustainable development in our country.The main results are described as follows:1.With root ventilation immersion method and high performance liquid chromatography(HPLC) technology, the vanillin and cinnamic acid content in eggplant root secretion and dynamic change were studied to clarify the sense of material accumulation and crop growth and the relationship between the continuous cropping years. Cinnamic acid and vanillin were existed in eggplant root secretion, rhizosphere and continuous cropping soil, and the contents of the two substances were different in growth period and continuous cropping years. Later the eggplant growth period and longer the continuous cropping years, higher the content was. With the extension of eggplant growth period, the content of cinnamic acid and vanillin in the root secretion and in the rhizosphere increased, and the content of cinnamic acid was lower than the vanillin, and the content of cinnamic acid in root secretion is 1.04%～ 4.40% of vanillin and cinnamic acid in the rhizosphere is 3.30%～25.00% of vanillin.Along with the increasing of planting years, vanillin and cinnamic acid content in the soil increased, and cinnamic acid accumulated average year 0.101μg.g-1, vanillin 0.372μg.g-1, and cinnamic acid content in soil was 17.08%～27.09% of vanillin. With the increase of crop growth period and plantation age, vanillin and cinnamic acid content in root secretion and soil presented the increasing trend. We infer that cinnamic acid and vanillin in eggplant root secretion could enter into the rhizosphere soil, stayed in soil after the changes such as migration and transformation, therefore lead to the accumulation of allelochemicals in different degree.2. With the bioassay and field simulation test, the allelopathy of vanillin and cinnamic acid was verified, the influences of the allelochemicals on different receptors (eggplant itself, other crops, verticillium wilt fungus) were revealed, and the relationship between allelopathy and continuous cropping obstacle was clarified.Intraspecific allelopathy:vanillin and cinnamic acid on eggplant itself (Xi’an green eggplant and Liao eggplant) with allelopathy characterized by "low to promote high inhibitory effect". Cinnamic acid (0～0.1 mmol·L-1) and vanillin (0～0.5 mmol·L-1) promoted the eggplant seed germination. seedling growth, and enhanced the capacity of plant growth and metabolic activity. With the increase of the concentration (cinnamic acid 0.1～4 mmol·L-1 and vanillin 0.5～4mmol·L-1). seed germination and seedling growth were restrained, the growth metabolism ability was reduced, showed significant poison effect. Xi’an green eggplant inhibition degree was stronger than Liao eggplant, and cinnamic acid strength was greater than vanillin.Interspecific allelopathy:vanillin and cinnamic acid on interspecific crops (red eggplant, bam, tomatoes, peppers) were characterized with allelopathic effect, but there were certain differences.With cinnamic acid (0～0.5mmol·L-1)and vanillin (0～1mmol·L-1), the seed germination,seedling growth,physiological and biochemical metabolism of red eggplant, bam, tomatoes and pepper were promoted; with the increase of the concentration (cinnamic acid 0.5～4 mmol·L-1 and vanillin 1～4mmol·L-1), the above indicators was restrained. The roles of cinnamic acid and vanillin are red tomato> bam, chili> tomatoes,respectively. Allelopathic effects on seed germination rate were particularly outstanding, pepper germination rate was less than 50% of tomatoes.Microbial allelopathy:the allelopathy of vanillin and cinnamic acid inhibited or promoted the spore germination and mycelial growth of eggplant verticillium wilt pathogen, tomato blight pathogen, pepper blight pathogen. The effect of vanillin and cinnamic acid on the spore germination was "low concentration to promote or high to inhibit", and the allelopathic effect on mycelial growth was not obvious. Cinnamic acid (0～0.5mmol·L-1) and vanillin (0～0.1mmol·L-1) inhibited spore germination, and cinnamic acid (0.5～4mmol·L-1) reduced the inhibited effect on spore germination, vanillin (0.1～4mmol·L-1)promoted the spore germination. Cinnamic acid (0～0.1 mmol·L-1) on the mycelium showed weak promoting, cinnamic acid (0.5～4mmol·L-1) showed weak inhibitory effect; in addition to the concentration of 0.1mmol·L-1, the rest of concentrations of vanillin and Ommol·L-1 treatment had no difference.The allelopathic effect of cinnamic acid and vanillin on eggplant, crops in the same family but not in the genus such as wild eggplant, tomatoes, peppers, and microbial bacteria (Verticillium wilt, etc.) could occur, which were autotoxicity and interspecific and microbial allelopathy, and showed that allelopathic effects of vanillin and cinnamic acid were characterised with diversity and multiplicity. Cinnamic acid and vanillin were generally existed in the eggplant root secretion, rhizosphere and continuous cropping soil, and constituted the complex relation with eggplant, other crops(wild eggplant, tomatoes, peppers)and microbial bacteria (Verticillium wilt, etc.). Although the receptor, ways, intensity and concentration range of allelopathy were different, but the rule showed the general consistency of "low to promote high to inhibit", namely when the allelochemicals reached a certain high level, it will produce more or less inhibition on eggplant and interspecific crops (wild eggplant, tomatoes, peppers), but promoted microbial bacteria (Verticillium wilt), which accorded with the continuous cropping obstacle phenomenon of growth and development of crops, severe diseases and insect pests. Th autotoxicity, interspecific allelopathy and microbial allelopathy of vanillin and cinnamic acid had intimate relationship with continuous cropping obstacle.3. With the simulated allelochemicals and pot experiment method, the regulation effects of grafting on content and allelopathy of vanillin and cinnamic acid were conducted. The secretion content of vanillin and cinnamic acid decreased in grafted eggplant root, especially vanillin.Grafting also reduces two substances accumulated in the eggplant rhizosphere, especially in middle and later stage. Grafting help relieve the stress of vanillin and cinnamic acid, especially for cinnamic acid stress. Under the stress of cinnamic acid and vanillin, the growth of grafted eggplant (plant height, stem diameter) and physiological metabolism (chlorophyll, photosynthesis, root conductivity, MDA, SOD activity, POD activity and proline content, soluble sugar content, soluble protein content, N, P, K absorption level) remaind the stronger advantage.4. Verifying the grafted eggplant resited cinnamic acid and vanillin stress, and revealing the mechanism of the grafting induced antioxidant protection systems, membrane stability, as well as the rhizosphere microecological environment change.Under vanillin and cinnamic acid stress, root growth and development of grafted eggplant (fresh weight, dry weight and root activity), leaf elements (N, P, K) content, chlorophyll content and photosynthetic capacity (net photosynthetic rate, stomatal conductance, transpiration rate, intercellular CO2 concentration) were higher than the root in tomato, and O2.- producing rate, H2O2 and MDA content of grafted eggplant were significantly lower than own root eggplant. It followed that grafting could induce eggplant resiste allelochemicals stress, maintain or enhance the advantage of the growth and physiological and biochemical metabolism activity.Under the vanillin and cinnamic acid stress, the osmotic regulation system, oxidation protective enzyme system, root membrane system stability of the grafted eggplant were better than the own root eggplant. Protine, soluble sugar, soluble protein content of grafted eggplant were higher than the own root eggplant.Grafting stimulated the activities of SOD, GPX, APX, DHAR and GR in eggplant, showed that they played an important role of reducing allelochemicals poison caused by the accumulation of reactive oxygen species. CAT activity of grafted eggplant decreases obviously, and POD activity decreasing or difference was not significant, showed that the CAT, POD may not be the key enzyme of clearing H2O2 in grafted eggplant. Under the stress of vanillin and cinnamic acid, plasma membrane of P-H+ATPase, P-Ca2+ATPase and vacuole membrane V-H+ATPase, V-Ca2+ATPase, V-H+ PPase of grafted eggplant were generally higher than the own root eggplant, P-Ca2+ATPase, V-Ca2+ATPase of vanillin and cinnamic acid reaction was more sensitive. Under the stress of vanillin and cinnamic acid, plasma membrane redox systems, the oxidation rate of NADH and NADPH, Fe (CN)63+ and EDTA-Fe3+ reduction rate of grafted eggplant were higher than the own root eggplant. Thus, grafting induced plasma membrane P-H+ATPase, P-Ca2+ATPase and vacuole membrane V-H+ATPase, V-Ca2+ATPase, V-PPase activity enhancement, enhanced the activity of plasma membrane redox system, protected the physiological function of plasma membrane from or adapted to stress of cinnamic acid and vanillin.Under the stress of cinnamic acid and vanillin, rhizosphere effects of bacteria and actinomyces in grafted eggplant strengthened, meanwhile rhizosphere effects of fungi weakened, and rhizosphere effect of soil enzymes (sucrase, urease and phosphatase) strengthened. Grafting increased the rhizosphere effect of the beneficial bacteria,and inhibited the rhizosphere effect of fungi,made the soil type change from fungi to bacteria,enhanced the rhizosphere effect of soil enzymes. To a certain extent, grafting repaired the negative influence of soil ecology caused by vanillin and cinnamic acid stress, had played a role in improving soil environment, which help to alleviate the occurrence of continuous cropping obstacle. |
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