24. Genetic erosion of rice in Thailand

In Thailand, populations of wild rice (Oryza rufipogon) grew in ditches along roads. A rapid progress of modernization and industrialization all over the country resulted in expansion of major roads and destruction of wild rice populations recently. To learn about the situation, wild rice populations at 17 sites along the road ftom Bangkok to Nonkai (Fig. 1) were observed in respect to their size and density in 1983 and 1991. At the same time, replacement of indigenous rice cultivars with improved ones during the eight years was observed at 19 sites (Fig. 1), so as to estimate the level of genetic erosion in cultivated rice.

During the eight years, six wild-rice populations observed either were destroyed or reduced in size and/or density. In particular, four sites within 150 km of Bangkok were heavily disturbed by the expansion of the road, or by construction of factories, resulting in disappearance of the wild rice. At other 11 sites far from Bangkok, wild-rice populations were maintained without remarkable changes in size and density during the eight years. Thus, the genetic erosion of wild rice has become severe with industrialization, without particular changes in natural condition.

Genetic diversity in cultivar populations has also been reduced during this period. In 1983, we collected indigenous glutinous cultivars at all 19 sites. In 1991, however, we found only improved cultivars, either glutinous or non-glutinous at 11 out of the 19 sites (Fig. 1). In a small village near Khon Kaen, the biggest city in Northeast, more than 20 indigenous glutinous and non-glutinous types had been found in 1983, but an improved non-glutinous and two improved glutinous cultivars were found in 1991. Not only indigenous cultivars but the glutinous trait was replaced by modernization.