Global environmental changes caused by natural and human activities have accelerated
in the past 200 years. The increase in greenhouse gases is predicted to continue to
raise global temperature and change water availability in the 21st century. In this
Review, we explore the profound effect the environment has on plant diseases - a susceptible
host will not be infected by a virulent pathogen if the environmental conditions are
not conducive for disease. The change in CO2 concentrations, temperature, and water
availability can have positive, neutral, or negative effects on disease development,
as each disease may respond differently to these variations. However, the concept
of disease optima could potentially apply to all pathosystems. Plant resistance pathways,
including pattern-triggered immunity to effector-triggered immunity, RNA interference,
and defense hormone networks, are all affected by environmental factors. On the pathogen
side, virulence mechanisms, such as the production of toxins and virulence proteins,
as well as pathogen reproduction and survival are influenced by temperature and humidity.
For practical reasons, most laboratory investigations into plant-pathogen interactions
at the molecular level focus on well-established pathosystems and use a few static
environmental conditions that capture only a fraction of the dynamic plant-pathogen-environment
interactions that occur in nature. There is great need for future research to increasingly
use dynamic environmental conditions in order to fully understand the multidimensional
nature of plant-pathogen interactions and produce disease-resistant crop plants that
are resilient to climate change.