Growing in their natural environments, the majority of plants remain healthy.
There may be some flecking or leaf distortions, but most plants compete
effectively and produce the next generation. This relative vigour is because
plants have evolved an effective immune system that protects each of their
cells from the majority of pathogens and pests. Only parasitic strains that
have developed mechanisms to overcome multiple layers of plant innate
immunity are able to invade and cause disease. Once disease takes hold it
can be devastating, particularly in plant monocultures that have a narrow
genetic base. The predicted increase in numbers of human beings having to
survive on our planet, as areas of fertile soil to grow crops become more scarce
and production costs soar, brings into sharp focus the need to understand
better molecular processes of plant disease and plant disease resistance. The
majority of the world’s populations still battle against malnutrition, hostile
environments and crop infestations. A heavy reliance on pesticides both in
Western agricultural systems and in the developing world helps to maintain
crop yields but is environmentally damaging and costly. The impetus has
therefore never been stronger to comprehend better how pathogens evolve to
infect particular plant species, how certain plant genotypes naturally defend
themselves against pathogen infection and how plant disease resistance is
executed at the level of individual cells, whole organisms and ecosystems.