Effect of fruit order, polyethylene mulch colour and early forcing on the fruit quality of tunnel-grown strawberry cv. 'Korona'

The effects of fruit order, polyethylene mulch colour and early forcing on the biochemical compounds (BCs) vitamin C (L-ascorbic acid), percentage soluble solids (degrees Brix), total acids, total anthocyanins, total phenolics and ellagic acid of strawberry (Fragaria x ananassa cv. 'Korona') were examined. The study was conducted in three consecutive years on fruit taken from a split-plot design involving a tunnel. There were large differences in fruit season and yield between the first and second fruiting years, reflected in the differences between levels of examined BCs of fruit orders, which ranged differently. The differences observed in degrees Brix and total acids were not sufficient to have a major effect on fruit taste. Using white polyethylene mulch (WM) increased the degrees Brix-value in one of the three years of the study and vitamin C in all years compared to brown polyethylene mulch (BM). Total acids were completely unaffected by mulch-colour during the whole course of the study. The contents of total phenolics, total anthocyanins and ellagic acid were examined only for the last year, and no significant effect of mulch colour for total anthocyanins was observed, while ellagic acid and total phenolics increased on WM compared to BM. Forcing made the plants fruit four or seven days earlier in the first and second year, respectively, but had no influence on the examined BCs. However, forcing strongly reduced fruit size and increased the percentage of malformed fruits in one year.