Light is essential for plant life. It provides a source of energy through photosynthesis
and regulates plant growth and development and other cellular processes, such as by
controlling the endogenous circadian clock. Light intensity, quality, duration and
timing are all important determinants of plant responses, especially to biotic stress.
Red light can positively influence plant defence mechanisms against different pathogens,
but the molecular mechanism behind this phenomenon is not fully understood. Therefore,
we reviewed the impact of red light on plant biotic stress responses against viruses,
bacteria, fungi and nematodes, with a focus on the physiological effects of red light
treatment and hormonal crosstalk under biotic stress in plants. We found evidence
suggesting that exposing plants to red light increases levels of salicylic acid (SA)
and induces SA signalling mediating the production of reactive oxygen species, with
substantial differences between species and plant organs. Such changes in SA levels
could be vital for plants to survive infections. Therefore, the application of red
light provides a multidimensional aspect to developing innovative and environmentally
friendly approaches to plant and crop disease management.
