Role of Plant Tissue Cultures in International Exchange and Quarantine of Germplasm in the United States and Canada

Very few of the crops grown in the United States or Canada today evolved in North America.Ancestors of today's crops were brought to North America as the continent was being colonized (Waterworth, 1993).Although we enjoy an abundance of food, fiber, and aesthetic products, our crops are plagued by many production problems, including insects, diseases, weeds, and lack of crop tolerance to drought or poor soil conditions.Some crops cannot be mechanically harvested, yield poorly, or their products are highly perishable.To deal with this broad range of adversities, thousands of plant scientists are developing new cultivars that address aspects of the above problems.Foreign germplasm containing beneficial genes continues to be an important need of many genetics and breeding programs (White and Waterworth, 1996).Regrettably, hundreds of different kinds of insects and pathogens that exist overseas, and that have not yet invaded North America, could easily be imported with plant materials from other countries (Code of Federal Regulations, 2000;Foster, 1988;Kahn, 1979Kahn, , 1986;; Plant Protection Regulations, 1995;Waterworth, 1993).Among these pests are pathogens such as apple proliferation phytoplasma in pome fruits, and bacterial leaf blight of rice (Oryza sp.), which continue to cause immense losses in Europe (Waterworth, 1993) and Asia (Mew et al., 1988;Thurston, 1973).Prior to the enactment of regulations to exclude foreign insects and diseases from North America, many were accidentally imported with plant germplasm, and are now so widespread that we think of them as indigenous.Such diseases and their casual agents include: cherry leafspot (Coccomyces hiemalis Higgins); apple scab [caused by Venturia.inaequalis (Cke.)Wint.