An Experimental Red Fluorescent Film Has Cultivar-specific Effects on Lettuce Yield and Morphology

Glazing and covering materials used in protected cultivation (PC) are primarily selected based on cost, longevity, heat retention, and light transmission. They can also be engineered to modify transmission of the solar spectrum by the incorporation of fluorescent pigments. Fluorescent pigments typically absorb blue (B; 400–499 nm) and/or green (G; 500–599 nm) photons and emit longer wavelength red (R; 600–699 nm) and, to a lesser extent, far-red (FR; 700–750 nm) photons. However, the incorporation of fluorescent pigments into plastics typically decreases its transmission of photosynthetically active radiation (PAR; 400–700 nm). In small-scale studies, ‘Butter Crunch’ lettuce ( Lactuca sativa ) shoot fresh mass (SFM) increased by as much as 22% when grown under a red fluorescent (RF) film compared with that grown under an unpigmented film with approximately 25% greater transmission of PAR. The objective of this research was to quantify variation among five lettuce cultivars when grown under a similar experimental RF film in a small-scale and larger-scale greenhouse experiment. Lettuce was grown under an RF film or neutral-density shade that provided a 15% to 24% greater average daily light integral (DLI). The SFM of lettuce increased by up to 45% and yield (SFM per m 2 ) increased by up to 37% when grown under the RF film, but the magnitude of increase was cultivar-specific. The SFM increase was linearly correlated with the increase in single leaf area but not projected canopy area. This work demonstrates the potential of an RF film to increase the yield of some (but not all) lettuce cultivars compared with neutral-density shade materials. However, further research is necessary to explore potential benefits for other greenhouse crops and changes to crop morphology.