Abstract
The purpose of this study was to identify morphological, physiological and biochemical changes in response to photoperiod in Vitis genotypes. Experiments were conducted under greenhouse conditions using cold-sensitive Cabernet franc (CF, Vitis vinifera) and cold-tolerant Couderc 3309 (C-3309, V. riparia x V. rupestris) and Concord (CD, V. labruscana). Potted vines were exposed to short day (SD)(8 hr) or long day (LD) (16 hr) for four, six and eight weeks. Shoot growth, periderm formation, dormancy, freezing tolerance (FT) (LT50) and soluble sugar concentrations in leaf and bud tissues were examined. Shoot growth slowed in all cultivars under SD accompanied with increased periderm formation and dormancy depth. CD initiated these changes first, followed by C-3309 then CF. The three cultivars did not show differences in FT under LD with LT50 ranging between −6.1 and −8.1°C. However, FT increased by 0.7, 2.0, and 2.7°C after four, six, and eight weeks under SD, respectively. FT of CD increased after four weeks; whereas C-3309 and CF did not change until after six weeks of SD treatment. Among all sugars, raffinose showed distinctive responses associated with photoperiod, remaining low and similar (0.5 to 2.3 mg/g DW) under LD. Under SD, raffinose concentration was generally higher ranging from 2.2 to 5.7 mg/g DW in leaves and 1.6 to 3.7 mg/g DW in buds, with cold-tolerant C-3309 and CD accumulating higher concentrations compared to cold-sensitive CF. These results suggest that raffinose accumulation might be an early step in response to photoperiod coinciding with slowed shoot growth, the induction of endodormancy and the initial acquisition of FT.
- ©2013 by the American Society for Enology and Viticulture
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