The studies have been carried out to investigate the influences of photoperiods on growth responses and rest induction of 3 grape cultivars, `Concord´ (Vitis labrusca Linne), `Delaware´ (Vitis labruscana Bailey), and `Golden Queen´ (Vitis vinifera Linne) during the summer and the autumn seasons in 1984.
The growth of grapevines was significantly increased by long day or light interruption (nightbreak) with 1 hour of red radiation in the middle of dark period, while decreased by short day treatment in all 3 cultivars when compared with those of natural photoperiod treatment during the summer or the autumn seasons.
Grapevines received short day treatment for 2 months during the summer season showed deep rest in `Concord´ cultivar, whereas shallow rest was noticed for those of `Delaware´ and `Golden Queen´ cultivars. However, long day, night-break and natural photoperiod treatments did not induce the rest in all 3 cultivars.
Grapevines received short day and natural photoperiod treatments for 2 months during the autumn season showed very deep rest in `Concord´ cultivar. Relatively deep rest was seen in short day treatment, whereas shallow rest was induced in natural photoperiod treated `Delaware´ and `Golden Queen´ cultivars. However, rest was not induced in long day or night-break treatments for all 3 cultivars.
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