Bioassay, Isolation And Identification Of Herbicidal Active Substance Of Tithonia Diversifolia

Plant-derived herbicide has received much more attention with the increase in environmental and ecological pressure nowadays. Echinochloa oryzoides is a common weed in rice (Oryza sativa) cropland that significantly reduces its yields. This study screened out several plant species that can inhibit the germination of E. oryzoides seeds based on allelopathy, and evaluated their their allelopathic effects. Tithonia diversifolia was identified as the main plant species that has significant inhibitory effects. The study further examined the inhibitory effects on seedling growth of E. oryzoides and evaluated the security of transplanted rice, and found that the aboveground part of fresh T. diversifolia was the most valuable research target in controlling E. oryzoides in rice fields. Active allelopathic compounds were separated and one compound was obtained, with its allelopathic activity studied to establish a foundation for exploring plant-derived herbicide that could control E. oryzoides, and provide a reference for relevant research on natural herbicides.1. Twelve plants from21plants in12families that are common in Hainan were identified as useful in inhibiting seed germination of E. oryzoides based on allelopathy. Murraya exotica, Parthenium hysterophorus, and T. diversifolia were further identified that can have strong inhibitory effects on seed germination of E. oryzoides but little effects on seed germination of rice based on integrative effects of four concentration. These suggest that the three plant species have the potential to be explored as plant-derived herbicides that can inhibit E. oryzoides during their germination period.2. Effects of water extracts from T. diversifolia on seed germination and seedling growth of Cucumis sativus, Raphanus sativus, Zea mays, and E. oryzoides were studied. Allelopathic substances that can control E. oryzoides were screened out from water extracts of the aboveground part, stems and litter of T. diversifolia. Effects from different water extracts were various on the same target, and effects of the same water extracts were various on different targets. T. diversifolia could inhibit the growth of other crops through allelopathy.3. Effects of water extracts from aboveground part, stems and litter of T. diversifolia on the growth of transplanted rice plants were evaluated through pot experiments. After integrated weighing of indices such as biomass, seedling height, malondialdehyde content, peroxidase enzyme, superoxide dismutase enzyme, leaf chlorophyll content, carotinoid content, and chlorophyll fluorescence content of rice plants, this study confirmed that aboveground part of T. diversifolia could stimulate the growth of transplanted rice plants.4. Organic solvents such as95%ethanol, petroleum aeher, chloroform, ethyl acetate, and btanol were used to extract aboveground part of T. diversifolia through the activity tracking method, and gel and silica gel chromatography methods were used to isolate and purify compounds. One allelochemical was isolated from the aboveground part of T. diversifolia. Spectral analyses such as mass spectrum and nuclear magnetic resonance were used to identify the compound, and it was tagitinin A.5. Effects of tagitinin A on seedling growth of R. sativus, C. sativus, E. oryzoides, and Brassica campestris Linn. were measured, and the strength of inhibition increased from B. campestris, C. sativus, R. sativus, to E. oryzoides.