title: Assessing frost damages using dynamic models in walnut trees: exposure rather than vulnerability controls frost risks.
abstract: Frost damages develop when exposure overtakes frost vulnerability. Frost risk assessment therefore needs dynamic simulation of frost hardiness using temperature and photoperiod in interaction with developmental stage. Two models, including or not the effect of photoperiod, were calibrated using five years of frost hardiness monitoring (2007-2012), in two locations (low and high elevation) for three walnut genotypes with contrasted phenology and maximum hardiness (Juglans regia cv Franquette, J. regia × nigra 'Early' and 'Late'). The photothermal model predicted more accurate values for all genotypes (efficiency = 0.879; Root Mean Standard Error Predicted (RMSEP) = 2.55 °C) than the thermal model (efficiency = 0.801; RMSEP = 3.24 °C). Predicted frost damages were strongly correlated to minimum temperature of the freezing events (ρ = -0.983) rather than actual frost hardiness (ρ = -0.515), or ratio of phenological stage completion (ρ = 0.336). Higher frost risks are consequently predicted during winter, at high elevation, whereas spring is only risky at low elevation in early genotypes exhibiting faster dehardening rate. However, early frost damages, although of lower value, may negatively affect fruit production the subsequent year (R2= 0.381, P = 0.057). These results highlight the interacting pattern between frost exposure and vulnerability at different scales and the necessity of intra-organ studies to understand the time course of frost vulnerability in flower buds along the winter.
authors.affiliation: Department of Botany, University of Innsbruck, Sternwartestraße 15, A-6020, Innsbruck, Austria.|Université Clermont Auvergne, INRA, PIAF, F-63000, Clermont-Ferrand, France.|Bordeaux Sciences Agro, Institut des Sciences de la Vigne et du Vin, Ecophysiologie et Génomique Fonctionnelle de la Vigne, UMR 1287, F-33140, Villenave d'Ornon, France.|BIOGECO, INRA, Univ. Bordeaux, 33610, Cestas, France.
authors.forename: Charrier
authors.identifier: 0000-0001-8722-8822
authors.initials: C
authors.lastname: Guillaume
authors.affiliation: Centre d'Ecologie Fonctionnelle et Evolutive, UMR CEFE CNRS 5175, 1919 route de Mende, 34293, Montpellier cedex 05, France.
authors.forename: Chuine
authors.initials: C
authors.lastname: Isabelle
authors.affiliation: Université Clermont Auvergne, INRA, PIAF, F-63000, Clermont-Ferrand, France.
authors.forename: Bonhomme
authors.initials: B
authors.lastname: Marc
authors.affiliation: Université Clermont Auvergne, INRA, PIAF, F-63000, Clermont-Ferrand, France.
authors.forename: Améglio
authors.initials: A
authors.lastname: Thierry
mesh_terms: D005615:Freezing / Q000009:adverse effects; D005638:Fruit / Q000502:physiology; D031324:Juglans / Q000502:physiology*; D008954:Models, Biological; D010641:Phenotype; D017440:Photoperiod; D012621:Seasons; D013312:Stress, Physiological; D014197:Trees
keywords: abiotic stress; dormancy; frost hardiness; phenology; photoperiod; temperature