Effects of hydrogen cyanamide and garlic extract on dormancy release, yield, and fruit quality of low-chill apple cultivars at Debre Tabor, northwestern Ethiopia

Abstract

Abstract Incomplete dormancy release due to insufficient winter chilling is a major constraint to apple ( Malus domestica Borkh.) production in tropical highland environments. This study evaluated the effects of hydrogen cyanamide (1.5%), garlic extract (15%), and their combined application on bud phenology, reproductive performance, yield, and fruit quality of three low-chill apple cultivars (‘Anna’, ‘Dorsett Golden’, and ‘Princesa’) under Ethiopian highland conditions over two consecutive seasons (2023–2024). Data were analyzed using a linear mixed-effects model with repeated measures across the two growing seasons. Dormancy-breaking treatments significantly advanced bud break by 15–24 days and shortened flowering duration from 7 to 8 weeks in the control to 3–5 weeks in treated trees. The combined hydrogen cyanamide + garlic extract treatment produced the earliest bud break and the highest flowering percentage (up to 67%), fruit set (up to 19%), fruit number (up to 63 fruits tree⁻¹), and yield (5.0–6.0 kg tree⁻¹) across cultivars. Yield improvement was associated with increases in fruit number and fruit weight. Significant cultivar × treatment interactions ( P < 0.05) were observed for most phenological and reproductive traits, demonstrating differential cultivar responsiveness to dormancy-breaking agents. Conversely, total soluble solids and fruit firmness were not significantly affected by treatment, cultivar, or their interaction ( P > 0.05). These findings indicate that combining low-chill cultivars with dormancy-breaking treatments partially compensates for inadequate winter chilling and improves apple productivity under tropical highland conditions.