Light quality management in fruit orchards: physiological and technological aspects
Light quality (sunlight spectrum) management promises to provide a new technological alternative to sustainable production in horticultural crops. However, little information exists about physiological and technological aspects on light quality management in fruit crops. Sunlight composition changes widely in orchard canopies, inducing different plant responses in fruit trees mediated by phytochrome (PHY) and cryptochrome (CRY) activity. High proportion of far-red (FR) in relation to red (R) light increases shoot elongation, while blue (B) light induces shoot dwarfing. Red and ultraviolet (UV) light increases fruit skin anthocyanin synthesis, while FR light shows a negative effect. Red and B light can also alter leaf morpho-physiological traits in fruit trees, such palisade thickness, stomatal aperture, and chlorophyll content. Besides improvement of photosynthetically active radiation (PAR) availability, the use of reflective films improves UV and R light proportion, with positive effects on PHY mediated-responses (fruit color, fruit weight, shoot growth), as reported in apple (Malus domestica Borkh.), peach (Prunus persica (L.) Batsch), and sweet cherry (Prunus avium (L.) L.). Colored nets widely alter spectral light composition with effects on plant growth, yield, and quality in apple, kiwifruit (Actinidia deliciosa A. Chev. C.F. Liang & A.R. Ferguson), peach, and blueberry (Vaccinium corymbosum L.) orchards. Mechanisms of colored nets seem to be associated to photosynthetic and morphogenetic process regulated by PAR availability, R/B light proportion, and CRY activity. Alteration of light quality affects significantly fruit tree plant responses and could be a useful tool for sustainable (e.g. lower use of chemicals and labor-practices) management of yield and quality in modern orchards.