INCREASED LEVELS OF CALCIUM IN THE NUTRIENT SOLUTION IMPROVES THE POSTHARVEST LIFE OF POTTED ROSES

Experiments were performed on miniature potted roses (Rosa) to investi gate whether increasing the Ca concentration in the nutrient solution would increase the Ca concentration in the rose plant, resulting in be tter postharvest quality. The plants were watered during the whole pro duction period with six different nutrient solutions with Ca at 1.1 to 4.4 mM and varying meg ratios between Ca and the cations. During the postharvest period, plant characteristics were recorded at days 0, 11, 14, 18, and 25. Increasing Ca in the nutrient solution significantly increased the Ca concentration of the plants. However, the NH4 level ( 2% to 5% vs. 22% to 25%) also influenced the Ca concentration of the p lants. Leaves had the highest Ca concentration, which was more than tw ice the level in flowers and buds, stems and roots. There were no diff erences in dry matter content between treatments in roots or tops at m arketing stage. At the start of the postharvest treatment (day 0), pla nts from the highest Ca treatment had significantly fewer flowers than those in all of the other treatments due to delayed development. The number of good flowers increased from days 0 to 14 irrespective of tre atment, while a further increase to day 18 was observed in plants from the three highest Ca treatments (low NH4) due to a negative effect on flower longevity of low Ca and high NH4 in the three low-Ca treatment s. By day 25, the number of good flowers had decreased markedly in all treatments, but plants from the second-highest Ca treatment had signi ficantly more good flowers than plants from the other treatments. Flow er wilting was due to infection by grey mold (Botrytis cinerea) and a physiological condition that caused wilting that began at the petal ed ges with a dark discoloration. Infection with grey mold was negatively correlated with Ca concentration in the flowers. The physiological wi lting was seen earlier in plants from the treatments with high NH4 and is probably not related to Ca concentration in the flowers.