Use of bioclimatic indexes to characterize phenological phases of apple varieties in Northern Italy

The research was designed to characterize the phenological behaviour of dif ferent apple varieties and to compare different bioclimatic indexes in orde r to evaluate their adaptability in describing the phenological phases of f ruit species. A field study on the requirement for chilling units (winter c hilling requirement) and the accumulation of growing degree hours of 15 nat ive apple cultivars was carried out in a fruit-growing area in North West I taly (Cuneo Province, Piedmont). From 1991 to 1993, climatic data were coll ected at meteorological stations installed in an experimental orchard (Verz uolo, Cuneo). Four methods were compared to determine the winter chilling r equirement: Hutchins, Weinberger-Eggert, Utah and North Carolina. The Utah method was applied to determine the time when the chilling units accumulate d become effective in meeting the rest requirements. A comparison of the di fferent methods indicated that the Weinberger-Eggert method is the best: as it showed the lowest statistical variability during the 3 years of observa tions. The growing degree hour requirement (GDH) was estimated by the North Carolina method with two different base temperatures: 4.4 degreesC and 6.1 degreesC. More difficulties were met when the date of rest completion and the beginning of GDH accumulation was determined. The best base temperature for the estimation of GDH is 4.4 degreesC. Phenological and climatic chara cterizations are two basic tools for giving farmers and agricultural adviso rs important information about which varieties to choose and which are the best and the most correct cultivation practices to follow.