Caracterización del cultivar de manzano Gvu Yvyrá respecto a sus requerimientos de frío y polinización

Apple is the main crop among temperate deciduous fruit trees, both globally and in Uruguay. Varietal replacement is one of the main challenges in fruit production. 'GVU Yvyrá' is a new national apple cultivar, resulting from a cross between 'Red Delicious' and 'Condessa'. Understanding the chilling requirements and pollinators of new apple cultivars is essential for proper site selection and management. The general objective of this study was to characterize the chilling and pollination requirements of 'GVU Yvyrá' under productive conditions in southern Uruguay. To estimate its chilling requirements, 15 shoots were collected weekly from the GVU Yvyrá, Red Delicious, and Condessa cultivars. The trial was conducted at INIA Las Brujas during the 2021–2022 season. The shoots were placed in buckets with water inside a growth chamber at 25°C and a 14-hour light photoperiod. Weekly evaluations were carried out, counting the number of sprouted buds. A cultivar was considered to have overcome dormancy when at least 50% of its buds had sprouted. Chilling accumulation was estimated using data from GRAS–INIA Las Brujas with the following models: Richardson (chill units, CU), Chilling Hours (CH ≤ 7.2°C), and the Dynamic Model (chill portions, CP). Pollination evaluation was carried out during the same productive season, in a commercial orchard of 'GVU Yvyrá' in full production (Melilla, Montevideo). The phenology of several potential pollinizers was recorded, selecting those with the most synchronized flowering for directed pollination: 'Anna', 'Dorsett Golden', 'Princesa', 'Eva', 'Condessa', 'Duquesa', and “Paco” (Malus floribunda). As results, 'GVU Yvyrá' exceeded 50% budbreak in the collection dated 08/12/2021, with an accumulation of 706.5 CU, 347 CH, and 32 CP. In this study, both 'GVU Yvyrá' and 'Condessa' showed low winter chilling requirements, with 'GVU Yvyrá' being less demanding in terms of growing degree accumulation. All evaluated pollinizers showed higher fruit set rates and seed numbers than the self-pollination controls, with the crab-type selection “Paco” and 'Eva' showing the greatest flowering synchrony with 'GVU Yvyrá'. 'Anna' had the earliest flowering, with 38% synchrony, and 'Princesa' the latest, with 65% synchrony. For proper orchard management of this cultivar, any of these four pollinizers —even in combination— can be used to achieve adequate fruit set in commercial orchards. This information should be complemented with plantings of this cultivar in non-traditional apple-growing regions with lower chill accumulation, such as northern Uruguay, where flowering synchrony with pollinizing cultivars may also vary.