Verfrühung von Süßkirschen unter geschlossener Folie

The sweet cherry cvs. ‘Burlat’, ‘Earlise’, ‘Samba’, ‘Souvenir’, and clone M, all with early ripening, large, dark, red-black fruit, were cultivated at a spacing of 3.80x1.75 m under complete rain cover in a whole orchard at the Klein-Altendorf Research Station near Bonn, Germany during April and May 2004. Under such cover, these sweet cherry trees flowered 6–13 days earlier and their fruit ripened 12–19 days earlier than those from uncovered control trees, indicating shorter or enhanced fruit development and maturation in up to 1 week. The cover proved insufficient for frost protection at night, despite increased daytime air and soil temperatures (by as much as 15°C and 5°C, respectively). Trickle irrigation was used to overcome loss of soil moisture due to the rain cover. Burlat leaves grown under this cover were thinner and softer and contained less chlorophyll a, chlorophyll b, and total chlorophyll than the leaves of uncovered control trees, without limiting photosynthesis. In contrast, the chlorophyll content of clone M leaves grown under cover equalled that of uncovered controls. Three of the five cvs. employed developed fruit mass of 9–15 g (25–33 mm fruit diameter). Three-year-old sweet cherry trees on dwarfing GiSelA 5 rootstocks were more vigorous than those without cover and produced 3–4.5 kg fruit per tree. The cover had no adverse effect on fruit colouration. The cherries grown under cover were slightly smaller, softer, with attractive colouration, and tasted better due to increases in both sugar and acidity, with sugar:acid ratios of 25–30:1.