COMPARISON OF VARIOUS EFFECTIVE HEAT SUMMATION REQUIREMENT (GROWING DEGREE-DAY) CALCULATION METHODS ON DIFFERENT GRAPE CULTIVARS

Grapes are a fruit species that has attracted attention due to its proven positive effects on human health. However, vineyards will have to be relocated to new regions in the near future due to the increasing effects of global climate change. Although it is known that the genotypic differences of grape cultivars allow them to exhibit phenotypic plasticity in new ecologies, the suitability of different grape cultivars for new ecologies needs to be estimated via numerical data with high accuracy. In this study, the effective heat summation requirement (EHSR) values of 12 grape cultivars grown in the Adiyaman province of Turkey, in between different phenological growth stages were determined using 3 different daily average temperature (DAT) calculation methods and 3 different EHSR calculation methods. The results showed that the EHSR values of the grape cultivars changed according to the methods used to determine them, but the order among the grape cultivars was constant. The DAT-1 (24-h temperature average) and DAT-2 (daily max. and min. temperature average) methods can be used interchangeably to determine the EHSR values of grapes. The Winkler index was found to be the most appropriate of the methods tested, it clarified the differences between grape cultivars, was affected by daily temperature extremes to a lesser extent, and measured the heat summation requirements between the bud burst (BB) and full bloom (FB) stages in grapevines most accurately. In addition, according to the EHSR value, there was a weak linear relationship between the BB-FB and veraison (V)-maturity (M) stages and a strong linear relationship between the FB-V, V-M, and BB-M stages. Moreover, the earliness of ripening in grape cultivars was caused by the shortness of the time elapsed between veraison and maturity.