Light attenuation effects on productivity, yield and fruit quality of Cranberries under Massachusetts conditions. Brian Makeredza, Giverson Mupambi and Peter Jeranyama University of Massachusetts Cranberry Station, 1 State Bog Rd, East Wareham, MA 02538 Cranberry (Vaccinium macrocarpon Ait.) is a fruit of significant commercial importance in North America. The fruit is consumed for its high vitamin C and antioxidants such as phenols, including anthocyanins and quercetin. Radiation stress poses significant challenges to production of high-quality marketable cranberries. Elevated exposure to high visible and ultraviolet (UV) light negatively impacts physiological and stress defensive mechanisms of the fruit, made up of biochemicals such as antioxidants, pigments and organic acids. We investigated the effects of light levels and quality on the productivity of two cranberry cultivars, Stevens’ and ‘Mullica Queen’ at two different sites. A sun exposed control was compared to three light reduction treatments. The treatments were two shade net treatments that filtered 17% and 34% visible light and a particle film spray (Raynox®), that filtered UV light. Sensors were installed to log micro-climatic weather conditions. Net carbon assimilation, stomatal conductance and transpiration were measured at the green, blush and full red stage of fruit development. The ratio of carbon isotopes as described by the δ13C value were assessed to determine carbon discrimination as a stress indicator. Fruit quality parameters measured at harvest were flesh firmness, titratable acidity (TA), total soluble solids (TSS), total anthocyanins (TAcy) and fruit rot. Raynox®, did not have an effect on carbon assimilation, yield and fruit quality. Reducing visible light did not affect stomatal conductance and transpiration but decreased carbon assimilation and yield but the effects were not statistically significant in some cases. Micro-climatic conditions under shade nets were conducive to the development of cranberry fruit rot which consequently contributed to yield reduction of marketable fruit. There were no differences in carbon isotope composition indicating no differences in abiotic stress levels. Fruit firmness decreased with an increase in shading. Trends for TA and TSS were inconsistent and unclear between the cultivars, but TAcy was only impeded by reducing light up to 34% level. Keywords: Cranberry, shade nets, light levels, particle film spray, carbon isotope
