ABSTRACT
The development of useful ex situ germplasm collections, whether for genetic resource conservation or in support of crop improvement programmes, requires that plants be collected from various sites around the world (see Hummer, Chapter 3, this volume) and introduced to new locations. A goal of many germplasm repositories is to represent the global genetic diversity of plant genera in their charge. One of the risks associated with collection of plant germplasm, especially from wild sources, is the inadvertent introduction of diseases or other pests along with plants or seeds. Some of the world’s most destructive plant diseases have been the result of the accidental introduction of exotic pathogens during the importation of plant materials. Examples of such importations include downy mildew of corn and sorghum caused by Peronosclerospora sorghi (W. Weston & Uppal) C.G.Shaw, dutch elm disease (Ophiostoma ulmi (Buisman) Nannf.), white pine blister rust (Cronartium ribicola J.C.Fisch.), chestnut blight (Cryphonectria parasitica (Murril) Barr), and more recently karnal bunt of wheat (Neovossia indica (Mitra) Mundk.), sharka disease of Prunus sp. (Plum Pox Virus) and tomato spotted wilt virus (many hosts). Virus and virus-like diseases pose a special challenge as they are often symptomless in infected plants and require specialized tests to determine their presence. As plant breeders attempt to broaden the genetic base of our agricultural and horticultural crops there are increasing efforts to introduce new genetic material from areas of origin of the species involved. These introductions are often land races or wild species that are not closely examined for the presence of germplasm-borne pathogens.
