Red and blue light are the major wavelength which are absorbed by leaf tissue and used for photosynthesis while others, i.e yellow and green light are reflected giving the plants their natural color. Far-red light (FR), which is invisible to the human eye, is transmitted by green plant tissues and constitute an important signal for plants to sense neighboring vegetation. At high planting density, the absorption of red light and the reflection of far-red light lead to a decrease in the ratio between red and far-red light (R:FR). Upon detection of a low R:FR, plants elongate and move their leaves upwards (hyponasty) in order to outcompete their neighbors and capture more light above the canopy. These changes in plant architecture called “shade avoidance” have been shown to enhance plant susceptibility to herbivores and pathogens including B. cinerea.
In a thesis, Sarah Courbier investigated how low R:FR can manipulate defense responses of tomato plants towards B. cinerea. Through an RNA sequencing analysis, she investigated how low R:FR exposure interferes with immunity against B. cinerea following a 30-hour time course. She found that the increased susceptibility caused by FR-enrichment relied on a delay in pathogen detection and in plant defense activation compared to control conditions. The RNA sequencing results also hinted at altered carbohydrate metabolism. Plants experiencing low R:FR accumulate more monosaccharides (glucose and fructose) than plants in control conditions which was correlated with a faster development of the fungus.
Source: Utrecht University