Blue and red photoselective shadecloths modify pea height through altered blue irradiance perceived by the cry1 photoreceptor

The use of shadecloth is common in horticulture to reduce Summer heat load on crops; however, such shading can increase shoot elongation to undesirable levels. A possible solution is to use photoselective shadecloths to overcome the problem of shoot elongation. To examine this question, pea (Pisum sativum L.) plants were grown under no shade, 50% neutral shadecloth, or 50% blue, or 50% red photoselective shadecloths. Under the red and blue shadecloths, the blue fraction was altered, but there was little alteration in other wavelengths relative to neutral shadecloth or to sunlight. Relative to neutral shadecloth, shoot length was reduced significantly under blue shadecloth, and increased significantly under red shadecloth.The effect of the red and blue shadecloths appeared to be mediated by alterations in blue irradiance perceived by the blue light cry1 photoreceptor, as, unlike wild-type (WT) peas, cry1 mutant peas did not respond to the shadecloth treatments. Levels of GA1 were reduced under blue shadecloth in WT pea plants compared with neutral shadecloth, but not in cry1 mutant plants. This study demonstrates that photoselective shadecloths can be used to manipulate plant height and flowering in crops with a strong response to blue irradiance.