Development of a Night Interruption Light Therapy Delivery Apparatus for Field Treatment of Hop Plants

The short-day plant Humulus Lupulus, or hops, relies on night length to control growth. During relatively long nights, as is the case in Virginia in summer, hop plants do not grow as tall as they do in the northwestern US. Growth triggers in hop plants are partially controlled by photoreceptors called phytochromes, which respond to light. Of particular interest are those phytochromes sensitive to the red and far-red wavelengths of light. When exposed to red light, the inactive form of phytochrome (Pr - red) is converted to the active form (Pfr - far-red), the latter regulating growth processes. Whereas far-red light triggers Pfr conversion back to Pr. In order to counter the effect of longer nights on phytochromes, three types of LED-based, Arduino-controlled, light delivery structures are under development. With the use of spectrometers, measurements of intensity as a function of wavelength give a profile of the illumination delivered by each array. The most efficient type of LED light for hop plants can be determined by comparing spectral data with the desired peak wavelength of red light for conversion of Pr to Pfr. Further measurements can verify calculations of the effective intensity of the light at various distances from the source, suggesting treatment regimens.