Role of allelopathy in sustainable agriculture: use of allelochemicals as naturally occurring bio-agrochemicals.

摘要

Alleopathy is the process whereby plants release toxic compounds into the environment, resulting in a detrimental effect on neighbouring plants or its own sharing the same habitat. The toxic metabolites are released into environment through volatilization, leaching, decomposition of plant residues in soil and root exudation. The phenomenon was earlier found in agricultural practice by Theophrastus (372 to 285 BC), who reported the inhibitory effect of pigweed on lucerne. In 1832, De Candolle suggested that the soil sickness problem in agriculture might be due to exudates of crop plants. Since then, many scientists had reported the significance of toxic effects of plant residues decomposing in soil, leading to the reduction in crop productivity. The productivity of many crops (Sorghum bicolor, Medicago sativa, Oryza sativa, Asparagus officinalis, Phaseolus radiatus [Vigna radiata] and Saccharum sinensis [Saccharum sinense], among others) was reduced significantly after a continuous monoculture. The crop productivity declines due to crops produces phytotoxic substances in soil and the accumulation of phytotoxins causes the imbalance of microbial population, such as Fusarium oxysporum in soil. These harmful allelopathic effects could be reduced through rotations or improving soil drainage in the field. In a unique example of pasture and forest intercropping system, it was demonstrated that an aggressive kikuyu grass (Pennisetum clandestinum), was introduced into the deforested conifer land. The kikuyu grass suppressed the growth of weeds significantly, but was not harmful to the regeneration growth of conifers or seeding growth of other hardwood trees. The pasture-forest intercropping system, indeed, benefited the forest management by reducing the use of herbicides, saving expensive manpower and enhancing forage material for livestock. Finally, the author in recent years have developed a unique system of using the plant parts, leaves, twigs or roots of allelopathic plants to make a cocktail of agrochemicals to replace conventional herbicides, fungicides or insecticides resulting in avoiding the residual effects of agrochemicals and reducing the environmental deterioration. Using advanced biotechnology, the allelopathic genes can be introduced into crops which possess the allelopathic potential to suppress its competitive weeds in the field. Thus, allelopathy has played important roles in sustainable agriculture.