PHOTOPERIOD EFFECT ON PLANT GROWTH IN CRANBERRY

Rooted cuttings of four cranberry varieties (Vactinium macrocarpon Ait.) were subjected to 9 hr of daylight and supplemental low-intensity illumination to provide photoperiods of 9, 12, 15, 21 and 24 hr. Nine weeks after the beginning of photoperiod treatments, the cuttings were rearranged in new photoperiod regimes of 9, 15 and 21 hr for an additional 18 weeks.Longer photoperiods resulted in increased numbers of leaves, more shoots, greater elongation of shoots, and greater dry weight, with the maximum response generally at the 21-hr photoperiod. Growth in the 24-hr photoperiod (continuous light) was frequently inferior to that in the 21-hr. There were some significant differences between varieties in all measurements. Initial treatment effects did not completely disappear in subsequent photoperiod regimes. The greatest responses to long photoperiods in the second regimes took place in those plants which had previously received long days. A few plants growing in short photoperiod treatments formed flower buds.