Implications for a warmer, wetter world on the late blight pathogen: How CIP efforts can reduce risk for low-input potato farmers

This paper discusses the relationship between climate change and the risk associated with a notorious and devastating plant disease. Before exploring the topic in more detail, it is worth noting that the 150-year history of this disease has been characterized by changes in risk to small-scale potato farmers, although the factors affecting those changes were different from climate change. For different reasons, farmers have had to adopt new strategies to cope with increased disease severity. At times, adaptation has been successful, at times not - with dire consequences. Some adaptation strategies have led to undesirable externalities that eventually bring into question the sustainability of the system. All these issues are potential lessons for efforts to intervene in scenarios that are expected to unfold in a wetter and warmer world. Late blight of potato exploded into the public consciousness in the mid 1840s when the oomycete pathogen, Phytophthora infestans, was introduced into northern Europe. The new disease caused by this pathogen affected both foliage and tubers (Figure 1), devastating potato production with highly variable consequences in different regions. The most drastic consequences occurred in Ireland where late blight of potato was the proximate cause of the Irish Famine of the 1840s, which led to a rapid decimation of the Irish population due to both emigration, and starvation and hunger related diseases (Nelson, 1995). The case of Ireland is a clear example of farmers not employing successful adaptation strategies. The reasons for this are complex and involve socio-economic forces that go beyond the simple lack of technological solutions (Bourke, 1993). It is not clear how other northern European farmers adapted to late blight in the decades that followed the introduction of the pathogen, but potatoes continued to be produced during that period. Robinson (1996) hypothesized that there must have been relatively high levels of resistance in the potatoes grown, a situation that resulted from high selection pressure (susceptible potatoes died) and lack of other strategies. Apparently potato breeding and selection for resistance was an important activity in Ireland