Shade effects on chlorophyll content, gas exchange and nutrient content of cranberry vines exhibiting yellow vine symptoms

Abstract: Yellow vine (YV) on cranberry (Vaccinium macrocarpon Ait.) is a symptom of stress that might reduce upright net photosynthetic carbon assimilation (A) through both, stomatal effects, which reduce the internal CO₂ concentration (Ci), and nonstomatal factors. This study evaluated the shade effects on reversing the effects of YV symptoms in chlorophyll and nutrient content, and uprights gas exchange. Shaded vines were affected in the same way as unshaded yellow vines and their net photosynthetic carbon assimilation was not affected by stomatal activity in contrast with the normal green vines. However, A was not limited by stomatal activity ? 250 mmol m^-2 s^-1. Chlorophyll a concentration was positively correlated with A (r = 0.53 P? 0.05), shaded and YV had significantly lower total chlorophyll concentration relative to normal vines. Chlorophyll b was less affected by YV symptoms. Plant tissue were collected in autumn and analyzed for individual nutrient composition. Manganese levels were excessive in all samples; this was especially true for yellow vines, suggesting that the yellow vines may be under more water stress. Shading yellow vines did not change their nutrient composition relative to unshaded yellow vines. It is plausible that excess water on the bog is the major cause of the yellow vine as growers have a cultural practice of applying 25 mm of irrigation water a week regardless of the evaporative demand or field capacity.