The budburst stage is a key phenological stage for grapevine (Vitis vinifera L.), with large site and cultivar variability. The objective of the present work was to provide a reliable agro-meteorological model for simulating grapevine budburst occurrence all over France. The study was conducted using data from ten cultivars of grapevine (Cabernet Sauvignon, Chasselas, Chardonnay, Grenache, Merlot, Pinot Noir, Riesling, Sauvignon, Syrah, Ugni Blanc) and five locations (Bordeaux, Colmar, Angers, Montpellier, Epernay). First, we tested two commonly used models that do not take into account dormancy: growing degree days with a base temperature of 10 degrees C (GDD(10)), and Riou's model (RIOU). The errors of predictions of these models ranged between 9 and 21 days. Second, a new model (BRIN) was studied relying on well-known formalisms for orchard trees and taking into account the dormancy period. The BRIN model showed better performance in predicting budburst date than previous grapevine models. Analysis of the components of BRIN formalisms (calculation of dormancy, use of hourly temperatures, base temperature) explained the better performances obtained with the BRIN model. Base temperature was the main driver, while dormancy period was not significant in simulating budburst date. For each cultivar, we provide the parameter estimates that showed the best performance for both the BRIN model and the GDD model with a base temperature of 5 degrees C.
SUMMARYMature blades of wheat seedlings were induced to form fructan by excision and continuous illumination, and their sugars wete analyzed either 24 or 60 h after induction by both gel permeation and high performance liquid chromatography. The earliest accumulated fructan consisted mainly of J-kestose, nystose, bifurcose, and short oligomers rich in (2 -l)-linkages and branch point residues-After several days, fructan included more than fifty compounds, among which one-half of the total were heptamers or larger. Oligomers accumulated during longterm incubation contained a higher proportion of {2 -6)-linkages than those accumulated early after induction. Stems of field-grown wheat contained about the same amount of fructan as blades of induced seedlings, but with larger proportions of phlein oligomers initiatmg uith 6-kestose, phlein-Hke oHgomers initiating wdth bifurcose, and other branched oligomers enriched in (2 -• 6)-linkages. An 'elongation-trimming' pathway is proposed in which a (2 ^ l)-specific fructan fructosyl transferase and O-6 branching activity produce branched oHgomers rich in (2 * 1 )-linkages, and in which a fructan exo-hydrolase cleaves 1-linked terminal-fructosy! units selectively to have phlein-like oligomers resistant to further hydrolysis.
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