Genetic segregation for indicators of photoperiod control of dormancy induction in Vitis species

The timing of endodormancy induction and release is important for the economic production of grapes. The overwintering grape bud develops in the leaf axil and is paradormant during the growing season. Bud endodormancy is induced by a decreasing photoperiod and/or low temperature during autumn. In Vitis there is considerable variation in response to photoperiod, with some genotypes becoming endodormant in response to a decreasing photoperiod (SD) and others requiring low temperature to induce dormancy. A comprehensive understanding of the biological mechanisms involved in bud dormancy is needed to promote advances in selection and breeding, as well as developing improved cultural practices for dormancy management in existing cultivars. We have developed a genetic model system with variation in endodormancy initiation and chilling requirement for investigating the mechanisms regulating dormancy induction and release. This system includes: a long critical photoperiod (dormancy induction), cold hardy, lower chilling requirement V. riparia parent, a less cold hardy parent, Vitis sp. 'Seyval' ('Seyve Villard 5-276'), which has a higher chilling requirement and a short critical photoperiod and/or low temperature requirement for dormancy induction, their F₁, and F₂ and BC populations. Four morphological traits (shoot elongation, shoot tip abscission, summer lateral emergence and periderm development) have been identified in controlled environment studies as potential selection markers for early photoperiod responsiveness and endodormancy induction in Vitis. In a replicated field planting of the F₂ and BC populations, summer lateral emergence was used for determining photoperiod responsiveness. The progeny exhibit a range of photoperiod responsiveness. Analysis of this trait indicates that it is heritable and may be controlled largely by a single locus with the longer critical photoperiod response of the V. riparia parent being dominant. This genetic system provides a powerful tool for identifying and characterizing other markers for endodormancy induction and release in Vitis.