Phenological diversity and heat requirements of quince (Cydonia oblonga Mill.) genotypes

Characterizing the flowering behavior and thermal requirements of quince (Cydonia oblonga Mill.) genotypes is essential for guiding future breeding efforts and adapting cultivation practices under ongoing climate change. However, there is a lack of comprehensive data on quince flowering phenology and associated thermal requirements. In this study, we investigated the bud and flowering phenology of 47 quince genotypes originating from Türkiye over three consecutive seasons under Mediterranean climate conditions. Phenological stages including bud break, bud burst, first bloom, full bloom, and end of bloom were recorded and expressed as day of the year (DOY), while effective flowering period and heat requirements were also calculated. Genotype and year had a significant influence on all phenological traits recorded. Bud break was observed as early as DOY 44, and flowering ended by DOY 108.3. Effective flowering periods ranged from 3.30 to 7.67 days, with genotype 2423 exhibiting both the earliest bloom and the longest effective flowering period. Heat accumulation between BBCH code 07 (bud break) and BBCH stage 65 (full bloom) was calculated in terms of growing degree days (GDD: 151.42-236.42) and growing degree hours (GDH: Anderson: 4,770.57-7,570.56; Richardson method: 5,444.47-8,028.20). Genotypes such as 2162 required the least heat input, while genotypes like 2760 showed the highest thermal demand for flowering. This study represents the most extensive classification of flowering phenology and heat requirement in quince to date. Results offer critical insights for selecting climate-resilient genotypes, identifying suitable cultivation zones, and supporting varietal registration through standardized flowering class assignments aligned with UPOV guidelines.