Allelopathic Activity of Naturally Occurring Compounds from Mung


1Department of Biochemistry and Molecular Biology, Oklahoma. Agricultural ... Allelopathic chemicals are secondary plant metabolites that have roles i...
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Chapter 18

Allelopathic Activity of Naturally Occurring Compounds from Mung Beans (Vigna radiata) and Their Surrounding Soil Downloaded by NORTH CAROLINA STATE UNIV on October 26, 2012 | http://pubs.acs.org Publication Date: December 9, 1994 | doi: 10.1021/bk-1995-0582.ch018

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G. R. Waller , C. S. Cheng , Chang-Hung Chou , D. Kim , C. F. Yang , S. C. Huang , and Y. F. Lin 2

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Department of Biochemistry and Molecular Biology, Oklahoma Agricultural Experiment Station, Oklahoma State University, Stillwater, OK 74078-0454 Institute of Botany, Academia Sinica, Taipei, Taiwan 115, Republic of China Asian Vegetable Research and Development Center, Tainan, Taiwan Republic of China 2

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Continuous cropping of mungbean (Vigna radiata) presents a problem in certain parts of the world (such as Taiwan) where the plant is grown. Now we show that allelopathy may contribute as much as 10-25% of the growth inhibition of mungbean plants grown following mungbean plants. These plants have been found to be allelopathic, and their surrounding soil toxic also. Distribution of the phytotoxic activity showed it to be in the stems and the aerial parts (excluding the stems), with the roots causing little inhibition of the mungbean plant. Partitioning of the stem extracts with water and organic solvents showed that water extracts were most inhibitory to the mungbeans and lettuce; and the organic solvents were both inhibitory and stimulatory. Bioassay of compounds present in soils after mungbean harvest (72 h incubation) also showed inhibition of mungbean plants grown to maturity. The discovery of enhancement of growth of mungbeans by crude mungbean saponins was serendipitous; those plants showed quicker germination and enhanced growth; however, such treatment did not increase the yield.

Allelopathic chemicals are secondary plant metabolites that have roles in plantplant, plant-soil, plant-disease, plant-insect, and plant-predator interactions that may be beneficial or detrimental to the plant. Mungbeans (Vigna radiata L.) planted in soil just used to grow mungbeans (plant-soil interaction) can encounter and produce such secondary metabolites. Mungbeans, a crop plant of economic significance in Taiwan and many developing countries of the world, were not known to have allelopathic activity until the recent finding of Tang and Zhang (/). Isolation of the inhibitory compounds produced isovitexin, which was the most active of three Cglucosyl flavanoids found. The concept of allelochemical spheres was introduced, which extended their observation from the germinating seed to the plant root system (7), and many biologically active metabolites occur at the root-soil interface; (2) thus the rhizosphere can be an allelochemical sphere in the environment 0097-6156/95/0582-0242$08.00/0 © 1995 American Chemical Society In Allelopathy; Dakshini, K., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1994.

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Allelopathic Activity of Compounds from Mung Beans

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Downloaded by NORTH CAROLINA STATE UNIV on October 26, 2012 | http://pubs.acs.org Publication Date: December 9, 1994 | doi: 10.1021/bk-1995-0582.ch018

surrounding the plant in the soil. The C-glycosyl flavanoids that were identified and bioassayed are present predominantly in the seed coat, not in the growing tissue of the mungbean plants; however, they possess only a slight inhibitory activity toward lettuce seedlings, and even less so for mungbean seedlings. Their role as allelochemicals in lowering the production of mungbeans remains unknown. In 1980 the Asian Vegetable Research and Development Center (AVRDC) of Taiwan (3) noted that five continuous mungbean croppings showed lack of uniformity of growth patterns; the plants were smaller and produced fewer pods per plant, fewer and lighter seeds, and poor yields (only 25 kg/ha). By comparison, where mungbeans had not been grown for at least three cropping seasons, yield was 440 kg/ha. This led to the recommendation that a mungbean crop should not be followed by another such crop for at least three cropping seasons (J, 4). Among different crops (mungbean, soybean, tomato, Chinese cabbage, sweet potato, corn, crotalaria, sorghum, and buckwheat), mungbean was the most detrimental to a succeeding mungbean crop. In one instance, yields after mungbeans were 65 kg/ha compared to 346 kg/ha after tomato. A series of experiments using a plant culture system designed to determine whether an allelopathic agent existed in the mungbean plant was performed (Young, C. C , National Chung-Hsing University, Taichung, Tawain, personal communication). The results strongly indicated that the mungbean plant produces phytotoxic substance(s) in its aerial parts and its root system; however, he did not follow up this lead. A few years later the mungbean root disease in the Philippines was described and it was reported that the primary cause was not fungi; however, the researchers did not mention that allelochemicals from the mungbean plant might have an effect (5). Cheng (