| Pogostemon cablin is a plant of the Lamiaceae family, which is extensively cultivated in the Philippies, Malaysia and Vietnam and other Southeast Asian countries, as an important medicinal plants. P. cablin has good prospects for development, however consecutive monoculture problem of P. cablin was serious during the continuous cultivation, which always resulted in a significant reduction in yield and quality, root system underground performance degradation, root disease and rot, leaf yellowing, poor plant growth and even death of the whole plant, seriously affected the production of patchouli. Thus, it is necessary to commence studies on the causes and mechanism of its continuous cropping obstacles. In this paper, allelopathic effects and molecular ecological of patchouli were studied in order to provide a theoretical basis and technical support to achieve effective control of patchouli cropping obstacles.The allelopathy of roots, stems and leaves of P. cablin were studied by conducting the pots experiments on patchouli seedlings. The results showed that the leaves had highest allelopathic potential, followed by roots and steams at the concentration of1:10. As compared to the control, plant height was reduced by99.8%in the treatment with leaves extracts (1:10)(p<0.05). The SOD and POD activities showed an increase trend at the low concentration, followed by a decline phase at the high concentration of roots and leaves extracts (1:10). The concentration of roots extracts (1:25) increased SOD activity by284.2%and POD activity by99.5%(p<0.05) and the leaves extracts (1:25) increased SOD activity by71.2%and POD activity by137.5%. The concentration of leaves and roots extracts (1:10) increased MDA contents by158.3%and358.3%(p<0.05).The allelopathy of aqueous extracts made from rhizosphere soil were studied by conducting the pots experiments on patchouli seedlings. The results, on the one hand, demonstrated that the high strength (pure) treatment had the most autotoxic effects on growth parameters of P. cablin in all treatments, especially on root length. It reduced by147.1%. On the other hand, the total fresh mass was greatly reduced by the medium strength (1:1) and high strength (pure) soil extracts, and the decrement was19.6%and22.7%, respectively (p<0.05). Moreover, the high strength (pure) soil extract greatly increased the SOD and POD activity and MDA content, and their contents were30.7μg-1FW,1.6umol g-1FW and3.3μmol g-1FWh-1, respectively.The differences that8kinds of allelochemicals had some phytotoxicity on patchouli seedling growth were observed in our hydroponic experiments. The results showed that the p-hydroxybenzoic acid had the highest allelopathic potential. Plant height, root length and total fresh weight of patchouli seeding were greatly reduced by p-hydroxybenzoic acid, and the decrement was77.0%,42.0%and70.0%, respectively, at the concentration of200μM (p<0.05). The SOD and POD activities were also reduced by p-hydroxybenzoic acid, and the decrement was101.6%and437.4%respectively, at the same concentration.In this study, terminal restriction fragment length polymorphism (t-RFLP) technique was used for fingerprinting fungal and bacterial diversity in the rhizosphere soil sampled from the fields of P. cablin monocultured for1and2yr. The results showed that the type and quantity of bacterial were declined as compared to the control. Simpson and Evenness index were both decreased during the consecutive monoculture of P. cablin. The type and quantity of fungal were increased in1yr-soil, followed by a decline in2yr-soil, and the beneficial fungi was reduced in2yr-soil as compared to the control. The total potassium and pH of soil is the main factor which lead to changes of microbial diversity in the rhizosphere soil of P. cablin. Ralstonia solanacearum and Laccaria laccata were two major pathogenic bacteria and antagonistic fungus in rhizosphere soil of P. cablin. |
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