Wild rice (Oryza rufipogon-Griff.), a relative of cultivated rice (Oryza sativa L.), is common in natural habitats throughout Thailand (Chitrakorn 1985). Characteristics of wild rice include seed shattering, black seed coat, awns on seeds, red pericarp, and sensitivity to photoperiod (Oka 1988), The oldest farmers say that wild rice has always been a common feature of rice fields in Thailand. They and younger farmers as well recall that, even 20 y ago, it was found mainly in natural habitats on the edges of farm ditches, deep depressions, and swampy places, but rarely in rice fields. Weedy rice with characteristics of O. rufipogon has been recognized as a weed in rice fields, but the level of infestation had been quite low, until recently.
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