Synergistic Effect Of Autotoxins And Phytopathogenic Fungi On The Pathogenieity To Rehmannia In Consecutive Monoculture System

Rehmannia (Rehmannia glutinosa Libosch) is in the Scrophulariaceae family and is one of the most common and important medicinal herbal plants in China. However, the consecutively monocultured plants are prone to severe diseases resulting in reduced biomass, especially the tuberous products. In this study, the propagation system of Rehmannia was established, the autotoxicity of fibrous root was evaluated, and the host-specific pathogenic fungi were isolated from replanted soil and wilt plants of Rehmannia. Furthermore, the synergistic effect of autotoxins and phytopathogenic fungi on the consecutive monoculture of Rehmannia was explored. The main results were as follows:In this study, the experiments were conducted to evaluate the quality of Rehmannia due to consecutive monoculture, and to explore the decline in the quality of Rehmannia from the sides of soil micro-ecology (soil microbes and enzyme activities). The results showed that, the quality of Rehmannia from the origin region (Jiaozuo, Henan province) and production region (Linfen, Shanxi Province) were different, but the differences between the newly planted soil and monoculture soil were significantly higher than the differences in regions. The monoculture soils from the two regions both inhibited the seedling growth. The continuous cropping caused the reduction in the number of rhizosphere soil bacteria, accompanied by the increase of fungi and actinomycetes, resulted in the transition of soil type from "bacteria" to "fungi". Compared to the rotational soil, the activities of urease, sucrase and catalase in the continuous decreased significantly (P＜0.05), while the activities of polyphenoloxidase, cellulase and protease were slightly increased soil. But the phosphatase activity showed an opposite trend in the newly planted soil and monoculture soils from the two regions. Therefore, we speculated that autotoxicity changed the soil micro-ecology, affected soil enzyme activity, thereby reduced Rehmannia to absorb nutrients.To establish the technical system of rapid propagation, the root tuber, leaves, apical buds, and radical buds of Rehmannia were cultured, and the results showed that using the radical buds as explants was best. Further, by optimizing the culture condition, the rapid propagation system of Rehmannia was established base on of radical buds inducing, which is MS+6-BA1+N AA0.1for induction, MS+6-BA0.3+NAA0.2for prolifera tion, and MS+PP3330.1for rooting. The cultivated aseptic seedlings grew in good condition and were used as material for the further study. The evaluation of potential autotoxicity showed that, fibrous root extract, replanted soil extracts and root exudates could inhibit the growth of Rehmannia glutinosa under the same concentration, and the fibrous root showed the strongest inhibitory effect. Four groups of autotoxic compounds from the aqueous extracts of the fibrous roots were isolated and characterized. The ethyl acetate extracts of these water-soluble compounds were further analyzed and separated into five fractions. Among them, the most autotoxic fraction (Fr3) was subjected to GC/MS analysis, resulting in32identified compounds. Based on literature, nine compounds were selected for testing their autotoxic effects on radicle growth. Seven out of the9compounds were phenolic, which significantly reduced radicle growth in a concentration-dependent manner. The other two were aliphatic compounds that showed a moderate inhibition effect at three concentrations. Concentration of these compounds in soil samples was determined by HPLC. Furthermore, the autotoxic compounds were also found in the top soil of the commercially cultivated Rehmannia fields. It appears that a close link exists between the autotoxic effects on the seedlings and the compounds extracted from fibrous roots of Rehmannia. Further analysis found that the autotoxic compounds not only resulted in membrane lipid peroxidation, the increasing of membrane permeability and antioxidant enzymes content, but also acted on plant indirectly by changing levels of endogenous phytohormones.In this paper,66fungi strains were isolated from replanted soil and wilt plants of Rehmannia. Next, morphological observation and ITS sequence analysis were employed to identify the strains. The results showed that66fungi strains could be divided into phylums of Ascomycota, Zygomycota, Basidiomycota and Deuteromycotina. By the back infestation test, the strains of CCS038, CCS043, CCS025and CCS012were screened as host-specific pathogenic fungi of Rehmannia, they were grouped into Fusarium nivale, Fusarium oxysporum, Aspergillus flavus and A spergillus fum igatus re specti vely.Finally, the synergistic effect of autotoxins and pathogenic fungi was discussed. The autotoxins especially ferulic acid and p-hydroxy benzoic acid not only promoted the hypha growth, spores proliferation directly, but also upgraded the expression of signal transduction system and nutrition metabolization related genes. In addition, the expression of some pathogenic genes were enhanced, which caused more sever damage to rehmannia.