Abstract
Rehmannia is a medicinal plant in China. Autotoxicity has been reported to be one of the major problems hindering the consecutive monoculture of Rehmannia. However, potential autotoxins produced by the fibrous roots are less known. In this study, the autotoxicity of these fibrous roots was investigated. 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 (Fr 3) was subjected to GC/MS analysis, resulting in 32 identified compounds. Based on literature, nine compounds were selected for testing their autotoxic effects on radicle growth. Seven out of the nine compounds 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.
Highlights
Rehmannia (Rehmannia glutinosa Libosch) is in the Scrophulariaceae family and is one of the most common and important medicinal herbal plants in China
Our results demonstrate that the compounds isolated from ethyl acetate-soluble extracts of Rehmannia fibrous roots had the most auto-inhibitory effects on the seedling growth
The 7 phenolic compounds and 2 aliphatic acids selected for testing the inhibition effects showed a significant suppressive function on the seedling growth
Summary
Rehmannia (Rehmannia glutinosa Libosch) is in the Scrophulariaceae family and is one of the most common and important medicinal herbal plants in China. It is perennial and its fresh or dried tuberous roots are used as a high demand traditional Chinese medicinal ingredient for hematologic conditions, sedation, insomnia and diabetes [1,2]. Its commercial cultivation has been practiced for almost 1500 years in China. The consecutively monocultured plants are prone to severe diseases resulting in reduced biomass, especially the tuberous products. The farmers commonly limited the cultivation on a same plot once every eight years. Less desirable areas outside Jiaozuo had to be used for the planting with decreased tuber yields and lower product quality [3]
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