| Allelopathic autotoxicity is an important factor to cause continuous cropping obstacle in flue-cured tobacco. The effect of allelopathic autotoxicity and preliminary exploration of abatement measures of continuous cropping obstacle in flue-cured tobacco were studied by field experiment and pot experiment and indoor culture method."Yunyan87"and"Yunyan97"and"K326" of flue-cured tobacco varieties were used as experimental material in this research. Firstly, in order to determine the the main source of allelopathic autotoxicity, this article was studied on the effects allelopathic autotoxicity in flue-cured tobacco through four main sources of substance of plant leaching, root exudates, root rhizosphere extracts and root residue decomposition. Then four resources were analyzed by GC-MS to identify types of allelochemicals and relative amount. At last, studies were carried on to detennine appropriate plants for rotation through biological effects of the strongest type among four sources of allelopathic autotoxicity on other crops seeds and their seedlings. Consequently, it would provide a scientific basis of abatement technology of continuous cropping obstacles in flue-cured tobacco. The main conclusions were as follows.Allelopathic effects of extracts from four sources on germination potential of Yunyan87and Yunyan97and germination rate of K326were highly significant (P<0.001), while on the germination potential of flue-cured tobacco K326was significant (P<0.05). The allelopathic effects of extracts from four sources on seed germination potential and germination rate of Yunyan87and Yunyan97and K326took on a trend of increasing firstly and then decreasing with concentration increasing, but the concentration of each extract to reach the highest point was different. Among the extracts from four sources, the promotion of root exudates on germination potential and germination rate of the three flur-cured tobacco varieties were weakest or the inhibition of those were strongest, especially high concentration of root exudates had significantly inhibited the germination potential of Yunyan87and Yunyan97and the germination rate of K326. Four sources all inhibited radicle elongation and promoted hypocotyl elongation for Yunyan87. Root exudates had the strongest inhibition on radicle elongation and weakest promotion in hypocotyl elongation for Yunyan87. High concentration of root exudates have a strong inhibitory effect on the elongation of radicle and hypocotyl for Yunyan97and K326.Allelopathic effects of extracts from four sources on plant height, stem diameter, maximum leaf length, maximum leaf width of Yunyan87and on height, stem diameter of Yunyan97and on maximum leaf length of K326were highly significant (P<0.001), while on the plant height, stem diameter of K326was significant (P<0.05). Allelopathic effects of extracts from four sources on content of soluble sugar and Malondialdehyde (MDA) and activity of phenylalanine ammonialyase and root activity of the three flur-cured tobacco varieties were all significant (P<0.05). The allelopathic effects of extracts from four sources on agronomic traits and physiological characteristics of Yunyan87and K326took on a trend of increasing firstly and then decreasing with concentration increasing, however, the concentration of each extract to reach the highest point was different. Among the extracts from four sources, the promotion of root exudates on agronomic traits and physiological characteristics of the three flur-cured tobacco varieties were weakest or the inhibition of those were strongest. Especially high concentration of root exudates had significantly inhibited maximum leaf length and maximum leaf width of Yunyan87and K326, and also had similar effects on content of soluble sugar of Yunyan97and root activity of K326. Furthermore, high concentration of root exudates had inhibited the absorption of nitrogen and phosphorus and potassium of leaves and whole plants for the three flue-cured tobacco varieties.Extracts from four sources for the three flue-cured tobacco varieties all contained9categories substances, that was, they were hydrocarbons, lipids, acids, ketones, alcohols, ethers, amines, aldehydes, phenols and so on. Furthermore, root exudates for the three flue-cured tobacco varieties were highest among the total of all materials. Hydrocarbons and lipids and ethers were of the highest in four allelochemicals sources of Yunyan87and K326. Hydrocarbons and lipids and ethers were also of the highest in plant leaching and root rhizosphere extracts and root residue decomposition for Yunyan97, while amines (15.71%) was the highest one, then ethers (5.73%) and lipids (5.25%) and hydrocarbons (3.2%) followed it in root exudates for Yunyan97. It contained48substances classified as7categories, in which23substances were included in hydrocarbons and14substances in lipids and the only one (Trimethylsilyl Ethers of Glycerol,11.76%) in ether, which was the highest among the total of all materials, in root exudates for Yunyan87. It contained47substances classified as6categories7, in which10substances were included in amines and17substances in lipids and13substances in hydrocarbons and only4substances in ethers, and the2,2,2-Trifluoro-N-Trimethylsilyl-Acetamide (13.97%) was the highest among the total of all materials, in root exudates of Yunyan97. It contained47substances classified as8categories, in which23substances were included in hydrocarbons and14substances in lipids and the only one in ethers, in which the1,23-three (Trimethylsiloxy) Butane (4.52%) was of the highest inamong the total of all materials, in root exudates of K326. The Octamethyltrisiloxane had a higher content in total hydrocarbons in root exudates for the three flue-cured tobacco varieties.Root exudates of the three flue-cured tobacco varieties all promoted seed germination potential and germination rate of Astragalus sinicus and Ryegrass and Leonurus Artemisia and Senna obtusifolia. And, with the concentration elevating, the promotion of root exudates of Yunyan87and Yunyan97took on a trend of increasing firstly and then decreasing. The promotion on Lolium perenne gradually increased with the concentration elevating, while the promotion on Astragalus sinicus and Leonurus Artemisia and Senna obtusifolia was reduced at high concentration, for root exudates of K326. Root exudates of the three flue-cured tobacco varieties inhibited germination potential and germination rate of Baby Cabbage, and the inhibitory were enhanced with concentration increasing. Moreover, Root exudates of the three flue-cured tobacco varieties promoted the elongation of radicle and hypocotyl in Astragalus sinicus, ryegrass, and Leonurus Artemisia, and inhibited the elongation of radicle in wheat.Root exudates of the three flue-cured tobacco varieties increased dry weight of shoot and root in Astragalus sinicus and ryegrass and Leonurus Artemisia. Root exudates had part inhibition of dry weight of shoot in wheat. It also had inhibition of dry weight of root in Senna obtusifolia, and the inhibition was enhanced with the concentration increasing. Effects of Root exudates of the three flue-cured tobacco varieties on MDA and activities of phenylalnine ammonialyase were significant (P<0.05). They significantly increased MDA content of Astragalus sinicus and Lolium perenne and Leonurus Artemisia, and also significantly enhanced activity of phenylalanine ammonialyase of Astragalus sinicus and ryegrass and Leonurus Artemisia and Senna obtusifolia and wheat. |
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