Genetic Erosion in the Tropics

Abstract

Vanishing of genetic resources within a cultivated plant species, genetic erosion, has been recognized as a serious problem in the field of agronomy. To estimate the rate of genetic erosion in wild rice, biomass (product of total area of the population X rice plant cover in percent) of 21 wild rice populations in northern and northeastern Thailand was measured in 1983 and 1991 (or 1992). The biomass of nine annual populations reduced to 13 percent during this decade, suggesting that they will vanish by the end of this century. The biomass of twelve perennial populations reduced to 73 percent. In perennial populations, weedy type caused by the introduction of genome of the neighbouring cultivars is increasing. Pure perennial wild rice is now being replaced by the weedy type. Genetic erosion occurs in cultivated rice also. Number of native varieties grown in northeastern Thailand reduced approximately to 50 percent during this decade. Genetic diversity within a field was also reduced as the introduction of high-yielding varieties. To prevent progress of the genetic erosion, gene banks were established for preservation of the genetic resources for major cultivated plant species, i.e., rice, wheat, corn, barley, beans. In case of rice, gene banks were built at the International Rice Research Institute (lRRI). National ones were also built in various countries. Gene banks have been playing important roles for preventing the vanishing of the genetic resources. However, they do not play effectively to maintain genetic diversity in agroecosystems. In situ conservation of the genetic resources, that is a new way of conservation in agroecosystem, is preferred. From the viewpoint of agronomy, low input sustainable agriculture(LISA) should be encouraged to keep agroecosystem sustainable.