Plant diseases have significant impact on food security. Our vulnerability resides principally on the fact that we grow, for the most part, monocultures that could be wiped out in a single season by a new pathogen. The potato famine in Ireland in 1880 is a historical example. A current one is a relatively new race of the wheat stem-rust pathogen that has spread beyond its area of origin.Most currently grown wheat varieties lack resistance to it. Accordingly, the task is to identify resistant varieties and incorporate that resistance into cultivated genotypes. Plant-disease impacts on food security and social stability can be significant, and in the last few years plants have been the sources of foodborne diseases by consumption of contaminated fresh produce.