Allelopathy in the natural and agricultural ecosystems and isolation of potent allelochemicals from Velvet bean (Mucuna pruriens) and Hairy vetch (Vicia villosa)

Abstract

6Our group has been engaged in the search for allelopathic plants in order to determine allelochemicals and its mechanism. In the course of this study, we developed new methods to discriminate and identify allelopathic actions from other competitive factors such as nutrients, light and water . We reported allelopathy in Velvetbean , Hairy vetch (Fujii et al. 1992, 1995, medicinal plants , and other species as well.In the course of those research, we established a new bioassay system that could demonstrate and assess the potential allelopathic action of plants. It was named "plant box method," and "sandwich method". This method involves mixed planting using agar medium, and is effective to study on the exudation of allelochemicals from leaves and/or roots. These methods can be applied to evaluate the allelopathic action of root exudates and leaf leachates.On the other hand, we realized a difficulty to use allelopathic plants directly to agriculture by itself, because other competitive factors such as light and nutrients are also acting on them in parallel. We decided to use the allelopathic factor together with such competition factors for plants growth. In this sense, cover crop is probably a good application of allelopathy. If other competition factors are the same, allelopathy will play an important role in weed suppression in combination with other factors. Some farmers suggested from their experiences that some ground cover plants suppress weeds drastically. There is a possibility that some cover crops could be used for practical weed suppression. In order to study its feasibility, we began to screen the allelopathic activity of cover plants by the plant box method and the sandwich method. Based on these primary selections, and experiences on the fields, we conducted a field experiment to select the most promising cover crop species for the weed control in orchard garden and abandoned fields. (Fujii et al. 1990a(Fujii et al. , 1990b: 70 plant species were tested on their allelopathy following the Richards' function method (Richards, 1959), which was proved to be suited for germination tests of lettuce and some weed plants ( Lehle & Putnam, 1982). In order to stop the action of enzymes, which degrade certain constituents of a plant, and to minimize the alteration of the constituent organic substances, the leaves, stems and roots were dried at 60°C for 24 hrs. One hundred mg of the dried samples was extracted with 10 ml water. Extracted mixture was sonicated for 60 sec to complete the migration of chemicals into aqueous solution. The extracts were filtered with Whatman No.4 filter papers. Ten lettuce seeds were placed in 4.5 cm diameter-Petri dishes soaking 0.5 ml of test solution on Whatman No.1 filter papers. The seeds on Petri dishes were incubated in the dark at 25 °C. Numbers of the germinated seeds was counted, and growth of hypocotyl and radicle were measured on the 4th day. Biological Sciences in Space, Vol.17 No.1 (2003): 6-13 Materials and Methods 1) Survey on allelopathic plants Allelopathy i...

The role of L-DOPA in plants

“…31 In studies with lettuce and chickweed, L-DOPA suppressed radicle growth in both by 50% compared with the control at 50 ppm; however, it exerted less of an effect upon hypocotyl growth and was virtually ineffective with regard to germination. 8 Soares et al 2 reported that L-DOPA was effectively absorbed by soybean, inhibited root growth and increased the contents of tyrosine and phenylalanine. In this plant, L-DOPA could have been detoxified toward phenylalanine, providing a substrate for phenylalanine ammonia-lyase (PAL), the first enzyme of the phenylpropanoid pathway.…”

“…Furthermore, its ability to control weeds and nematodes greatly reduces the need to apply artificial chemicals to the crops. 5,7,8 In addition, its cultivation in tropical areas is aimed at enriching the soil due to its ability to fix nitrogen. 9 Velvet bean has been intercropped with maize and rice in Nigeria and Japan, respectively.…”

Bioactive l-DOPA induced quinoprotein formation to inhibit root growth of cucumber seedlings

“…has high l-DOPA content (>5% in seeds). 2,3) l-DOPA selectively inhibits the growth of many plant and weed species. l-DOPA (0.1 mM) suppressed root growth (>50%) of 24 plant species from 9 diverse families irrespective of monocotyledonous and dicotyledonous, broadleaf and narrowleaf, and C 3 and C 4 .…”

Growth and Nutrient Accumulation of Winged Bean and Velvet Bean as Cover Crops in a Subtropical Region

“…The allelochemical activity of velvet bean has been attributed to L-DOPA, which is exuded from leaves and roots. Velvet bean contributes 200-300 kg ha -1 of L-DOPA to the soil each year (Fujii et al, 1991;Fujii, 2003;Nishihara et al, 2005). However, the allelochemical compounds of winged bean remain unknown.…”