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Allelopathy in South China agroecosystems.

Luo, Shiming1, 1 South China Agricultural University, Guangzhou, Guangdong, China

ABSTRACT- Chemical interaction is one of the key mechanisms within agroecosystem in the tropical and subtropical Southern China. Allelochemicals are important for the success of exotic species like Eucalyptus, Chromolaena odoratum, Mikania micrantha, Ageratum conyzoides to develop in new area. Auto-toxicity of tea, tomato, Casuarnia equisetifolia,and Wedelia chinensis were existed. It could explain the suppression of seed and seedling of tea under a well grown tea canopy, and the degradation of the C. equisetifolia community. It suggested that the choice of coexisting plants in the hydroponics system for tomato production must be very careful. It also reminded us that the effective level of allelochemicals for auto-toxicity may higher that for other plants. Allelopathic effects of the water extract from Bidens pilosa and volatile compounds from leave of Eucalyptus citriodora negatively correlated with the rainfall. The amount of volatile oil in Ageratum conyzoides was negatively correlated with soil nutrient condition. A. conyzoide infected by powdery mildew disease produced more volatile oil than the healthy plants. Acceptor plants were more vulnerable to allelopathic effect under suboptimal environment. Research on the physiological an biochemical mechanisms of allelopathic effect on receiver plant, rice seedling, by Secalonic Acid F (SAF) from fungi Aspergillus japonicus showed that the allelochemical reduced the activity of Superoxide dismutase (SOD) and Peroxidase (POD) of the receiver plant, destroyed the cell membrane system and increased cell electronic conductivity, hence decreased the photosynthesis and increased the respiration. Allelopathic effect of different mixture of allelochemicals from tomato on lettuce, cabbage, and radish, and from Ageratum conyzoide on radish showed that the effect of mixture is quite different from its individual components. Both augment effect and diminishing effect could be observed. Ageratochromene from Ageratum conyzoides could act as anti-juvenile hormone on insect, at the same time had inhibition effects on the growth of radish, ryegrass, barnyard grass, and on the pathogens like rice banded sclerotial blight and phytothora foot rot of pepper. Volatile oil from Mikania micrantha also had inhibitory effect on both plants and fungi.

Key words: Allelopathy, South China, Agroecosystem

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