In Vitro Production of Late Blight (Phytophthora infestans)-Resistant Potato Plants

Abstract

New challenges face the potato breeder, particularly in Europe and the former USSR. There is a need to adapt high-yielding Western processing varieties for potential new growing areas in eastern Europe (Bethell 1990). The threat of new genetic variability in the pathogen, Phytophthora infestans, resulting in more rapid changes in virulence and fungicide resistance, has increased with the spread of the A2 mating type outside Mexico (Spielman et al. 1991; Umaerus and Umaerus 1994). Resistance to phenylamide systemic fungicides is widespread (Parry 1990; Cooke 1992). There is also the possibility that the dithiocarbamates, the mainstay of chemical late blight control, may be withdrawn on environmental grounds. It has been estimated that in Ireland approx. 80% of the potato seed growers used dithiocarbamates alone or with systemic fungicides in late blight control. Should the dithiocarbamates be withdrawn, the problem of late blight control would be acute with the lack of adequate varietal resistance in commercially important cultivars and the toxicity to the crop of alternative copper- and fentin-based fungicides. These issues have been discussed by Parry (1990) and Cooke (1992).