Effects of Climate Change on Evolutionary Forces Agroecosystems and Food Crops

Apart from the specific changes in disease-infection cycle components, climate change is almost certain to be a strong driver of evolutionary change in plant and pathogen populations by interfering with host-pathogen interactions, gene expression and population dynamics (Harvell et al., 2002) (Table 4.2). Population genetic structure and disease dynamics are very influenced by pathogen-host-environment interactions through the action of evolutionary forces. McDonald and Linde (2002) identified five forces affecting pathogen populations: (i) mutation; (ii) genetic drift; (iii) gene flow; (iv) asexual and sexual reproduction; and (v) selection. Interspecific hybridization and gene expression or functionality also influence the composition of pathogen populations. Climate change could influence selection, an evolutionary force characterized by a directional process that leads to an increase or decrease in the frequency of genes or genotypes in a pathogen or pest population. These forces affect biological systems in various ways and influence epidemiological dynamics and pathosystems, depending on environmental conditions. Through its impact on temperature or humidity, climate change might select stronger individuals. However, predicting the potential responses of a pathosystem is very complex because of the multivariate nature of climate change and the multiple effects of the biotic components of the system, including the pathogen, its natural hosts (crops or weeds) and its natural enemies. Although most host-parasite systems are predicted to experience more frequent or severe disease occurrence with warming, a subset of pathogens might decline with warming, releasing hosts from disease (Harvell et al., 2002). Some examples of how climate change could influence evolu

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