Application of LED-interlighting for improving the yield of passive tunnel-grown bell pepper

Owing to the low radiant heat generation of light-emitting diodes (LEDs), they can be used to directly illuminate plants within their canopies, without inducing heat damage. This is known as ‘LED-interlighting’ or ‘intra-canopy illumination’, a technique typically implemented for high-wire vegetable crops in actively-controlled greenhouses. In this work, we report on the effects of red-green-blue (RGB)-LED interlighting applied for bell pepper grown in passive high tunnels in the Jordan Valley, Israel. Applying the ‘Spanish’ trellis system, rapid plant growth in the autumn results in a canopy that is tall, dense and extremely shaded at the center along most of the growth season. At the same time, the outer, exposed canopy regions are not light-limited. We found that application of daytime LED illumination within the canopy, which enhances photosynthesis and transpiration rates of the foliage therein, also resulted in an increase of the spring fruit harvest. Our results demonstrate the potential of LED-interlighting as a useful technique for improving fruit production at variable conditions in high tunnels, in which typically no active environmental manipulations are carried out. Yet, adaptation of this technique for use at the local conditions requires further optimization.