Plant pathogen evolution and climate change.
The earth's system is currently experiencing dramatic climate change, with predicted rates of global-mean temperature increase unprecedented in the past 1000 years. Also temperature patterns at the local scale and precipitation regimes are rapidly changing. Extreme climatic events are becoming more intense and frequent, especially on the regional scale. Such sudden environmental changes reduce the time for adaptation and increase the vulnerability of natural ecosystems. Plant pathogens have three major adaptive responses to climate change: to exploit the existing phenotypic plasticity, to migrate to areas with more suitable climate and/or to evolve new attributes. Plastic genotypes may quickly adapt to a broad range of environmental conditions, but if phenotypic plasticity is insufficient, migration and/or evolution (which are facilitated by large population size, mixed mating system and parasexuality) are the only options. Global trade in live plants, which is nowadays the main pathway of introduction of alien plant pathogens to new areas, further complicates the picture. Once introduced into a new environment, pathogens may adapt their lifestyle to new local hosts (host jump), or evolve by introgressing useful genes for adaptation through hybridization with resident species or horizontal gene transfer. The implications of climate change for plant pathogens are difficult to predict, but since pathogens have an array of adaptive mechanisms much wider than their hosts and shorter generation times, their opportunities to adapt/evolve will probably increase. New strategies for predicting and monitoring plant pathogen evolution need to be developed to prevent the spread of new plant pathogens on naive or vulnerable hosts likely weakened by climate change pressure.