FRUIT-SET AND THE EFFECTIVE POLLINATION PERIOD IN RED CURRANT AS AFFECTED BY NITROGEN-FERTILIZATION AND EXPOSURE TO RED-LIGHT

In three experiments in plastic tunnels, the effect of nitrogen fertil ization, exposure to red light and flower removal was evaluated on the fruit set of red currant (cvs Jonkheer van Tets, Red Lake and Rolan). In addition, the effective pollination period (EPP) was determined. N itrogen fertilization had no effect or only minor effects on fruit set , berry weight and seed number per berry. Exposure to red light was al so uneffective. Removing the terminal five flowers of a truss enhanced fruit set, but berry weight was not affected. The EPP was only 2-4 d. When pollination was delayed to 6 d after flower opening, fruit set w as the same as in the ''no-pollination'' control. Delay in pollination markedly reduced berry weight and seed number. Fruit set after self-p ollination was high but berry weight and seed number were clearly lowe r than after cross-pollination. In an additional outdoor experiment, r educing light intensity by 50% had no effect on fruit set.