The knowledge of the chilling requirements for breaking rest and flowering of fruit trees is necessary to properly select cultivars and to avoid losses due to an inappropriate cultivar selection in a particular geographical location. With the aim of providing an analysis using three models (Chilling Hours, Utah Model, and Positive Utah Model) to estimate the accumulation of winter chilling, quantifying its spatial variability and representing the spatial pattern throughout mainland Spain, temperature data from 72 meteorological stations, considering the 1975–2015 period, were utilized. The statistical properties of values corresponding to each winter chilling model were assessed and, later, they were mapped by means of an integrated geographic information system (GIS) and a multivariate geostatistics (regression-kriging) and algebra map approach. The results show that measures obtained with the three chilling models were highly related, which were used to visualize the spatial variability of the accumulated winter chilling considering each model. Moreover, the fact that elevation and latitude are related to the chilling hours enables their use as auxiliary variables to better estimate at unsampled locations and generate more accurate maps. Knowledge of the spatial patterns of chill accumulation in different areas of mainland Spain is of great importance when appropriate fruit trees and cultivars have to be selected. Moreover, if a high probability of satisfying the chilling requirements in any area is considered, quantile maps can be used instead of maps based on mean values. Finally, the potential spatial distributions of three sweet cherry cultivars were delineated using the obtained maps.
Pollen meiosis and chilling requirements in sweet cherry
