Transboundary diseases and pests refer to organisms that can be dispersed over a long distance beyond the national or geographical boundaries (e.g. mountains and deserts), such as rusts or migratory pests (e.g. locusts). Transboundary plant pests are also quarantine organisms that are absent from one region or reported under control in one country and could cause a threat if introduced. With the globalization of trade and international travel, quarantine measures and early intervention are essential to protect agroecosystems from the introduction of exotic pests and diseases and to prevent the establishment and spread of new epidemics. This implies the development and implementation of adequate policies, and the effective inspection and certification of seed and plant materials free from pathogens and pests (FAO, 2008). Precautionary measures are also necessary for endemic diseases characterized by the existence of physiological races. Winds disperse airborne pathogens such as soybean and cereal rusts over a long distance. Soybean rust caused by the Phakopsora pachyrhizi fungus has been invasive in South America since 2001 and was confirmed in the USA in 2004 (Oerke, 2006; Kumudini et al, 2008).
Recent examples show that wheat rust epidemics have emerged from the introduction of a new virulent race following global travel (Brown and Hovmoller, 2002; Hovmoller et al, 2008), highlighting the importance of public awareness of the need to avoid introducing pathogens or pests. In wheat, the rapid response of the scientific community and the support given to wheat research in reaction to the dispersal of Ug99, the aggressive race of stem rust caused by P. graminis f. sp. tritici, also illustrated how internationally coordinated breeding efforts, backstopped by advanced research institutes, can mitigate the threat caused by the migration of a race that is virulent against 90% of commercial wheat cultivars worldwide (Singh et al., 2008). The same principle applies to preventing the introduction of the vectors of viral diseases. The monitoring of emerging diseases and early diagnostic capacity to identify new problems in the field are therefore essential. Wheat blast, an emerging disease caused by Magnaporthe grisea (Duveiller et al., 2007), presently restricted to warmer growing areas in the Southern Cone, deserves attention in preventing the pathogen, or its wheat-affecting pathotype, migrating or being introduced into climatically comparable wheat systems in other regions.