Introgression and gene flow in Asian rice.

Our research investigates the degree of gene flow between wild and cultivated rice in Thailand and examines the consequences of gene flow and introgression in producing weedy rice. Oryza rufipogon, the wild ancestor of cultivated rice, can cross with cultivated rice, although the degree of crossability varies with both wild rice population and the specific cultivar of rice. In areas of Asia where O. rufipogon and O. sativa grow in close proximity, an increasingly common observation is the infestation of fields with weedy rice. Genetic studies indicate that weedy rice is the result of hybridization between wild and domestic rice. Weedy rice incorporates undesirable traits from the wild ancestor such as seed shattering, awns, and perennial growth form. Once in a farmer’s field, weedy rice can rapidly increase in frequency and may result in greatly reduced yields that in some extreme cases can result in abandonment of fields for rice cultivation. We have experimentally examined the consequences of gene flow between transgenic rice and wild rice by comparing the fitness of hybrid plants to that of parental strains of wild and transgenic rice. Transgenic rice used in this study contained a LEA protein that confers drought resistance. Transgenic x wild rice hybrids have similar to intermediate survivorship, growth rates, and seed production to that of the parental rice, under either standard or drought conditions. Interestingly, transgenic x wild rice hybrids have superior competitive ability compared to the parental strains. These studies in total indicate that, in at least part of O. rufipogon’s range, gene flow leads to the production of weedy rice that can significantly impact farmer’s yields. Greenhouse studies indicate that hybrids between transgenic rice and wild rice have fitness levels equivalent at least to wild rice, suggesting that issues of gene flow needs to be addressed in the widespread adoption of transgenic rice in Asia.