Effect of nitrogen rates and days of light exposure on greening evaluated by visual scale and chlorophyll meter of tubers of potato cultivars.

Preventing potato greening can be achieved by the adoption of appropriate pre-and post-harvest practices. This work aimed to evaluate the effect of nitrogen (N) rates on the greening of washed and unwashed tubers of the four most planted potato cultivars in Brazil during 25 days of light exposure. Four experiments were carried out in the autumn/winter in clay Cambic Red-Yellow Podzolic soil. Each experiment consisted of five N rates: 0, 50, 100, 200, and 300 kg ha -1 as ammonium sulfate applied in the furrows and one of the four potato cultivars, Agata, Asterix, Atlantic, and Monalisa. The experiments were arranged in randomized blocks with four replications. After harvest, commercial tubers from each experimental field plot were separated into two lots; washed and unwashed potatoes. Tuber lots were exposed to four 4-tube fluorescent light fixtures with 40 W for each tubes. After 2, 4, 6, 8, 10, 15, 20 and 25 days, the tuber greening was evaluated using a visual grading scale in a split plot design together with four replications. At 25 days of light exposure SPAD readings were also performed in tuber periderm. Washed tubers were greened more than unwashed tubers when measured by visual grading scale. Depending on the cultivar, the N rate affected the greening of washed and unwashed tubers when measured using a visual grading scale. For all cultivars, tuber greening intensity increases linearly per days of light exposure and N rates increased the greening of washed tubers measured using a SPAD meter.