Dormancy and Cold Hardiness in Vitis vinifera L. cv. White Riesling as Influenced by Photoperiod and Temperature

¹ Department of Horticulture and Landscape Architecture, Washington State University Irrigated Agriculture Research and Extension Center, Prosser, WA 99350.

Cold hardiness of Vitis vinifera L. cv. White Riesling was examined using controlled environments to establish the roles of photoperiod and temperature. Field-grown, potted plants were maintained for comparison. Gradually decreasing daylengths, when combined with constant warm temperatures, increased cane hardiness by 0.8°C, while primary bud hardiness was decreased by 2.7°C. Combining constant cool temperatures with gradually decreasing daylengths resulted in an increase in cane and primary bud hardiness of 1.3°C and 0.8°C, respectively. Long photoperiods and gradually decreasing temperatures increased cane and primary bud hardiness by 1.8°C and 1.1°C, respectively. Combining gradually decreasing temperatures and decreasing photoperiods was the most effective and caused increased hardiness of canes by 4.5°C and primary buds by 5.2°C, thus demonstrating a synergistic effect of these environmental factors. Depth of rest induced by these treatments was examined following cold hardiness evaluation. A chilling treatment facilitated the transition from dormancy to active growth.

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