Late blight of Tomato

Late blight (LB), caused by the oomycete Phytophthora infestans (Mont.) de Bary, is one of the most destructive diseases of tomato (Solanum lycopersicum L.) and potato (S. tuberosum L.) worldwide, causing significant economic losses annually. The success of P. infestans as a pathogen originates from its effective asexual and sexual life cycles, as well as its remarkable capacity to rapidly overcome plant resistance genes, a result of its high evolutionary potential. The most sustainable strategy to manage tomato LB would be to deploy an integrated system including cultural practices, fungicide application, and the use of cultivars with broad-spectrum genetic resistance against LB. Prior to the reemergence of LB in the late 1980s, cultural practices in combination with fungicide applications were highly effective measures to control the tomato LB. However, with the appearance of new and more aggressive isolates of P. infestans, many of which are resistant to LB-specific systemic fungicides, the greatest contribution to tomato LB control in the future will have to be through the development of cultivars with improved genetic resistance. Thus far, a number of major LB-resistance genes and quantitative trait loci (QTLs) have been identified in tomato and several breeding lines and cultivars, with improved resistance developed. Research is also underway to identify additional resistance genes or QTLs and to pyramid multiple resistance factors in order to develop stronger and more durable resistance. Further, as exemplified by the fast progress in potato LB research and conservation of LB signaling pathways between potato and tomato, detailed knowledge of the pathogen effectors in combination with high-throughput genomics technology will facilitate a better understanding of the LB disease and host-pathogen interactions, which in turn may lead to development of tomatoes with more durable resistance.