Biological and economic qualities of some apple hybrids

Six apple hybrids created at the Institute of Agriculture, Kyustendil (Bulgaria) were tested in 2012-2014. The trees were grafted on 'MM 106' rootstock and planted in the spring of 1998 at a distance 4.5×2.5 m. The trial was established in five replications (1 tree replication^-1). The flowering period, ripening time, tree growth, yield, morphometric (fruit weight and dimensions) and chemical properties (soluble solids, total sugars and titratable acids content) were determined. The earliest bloom was observed in hybrid 1/16 ('Winesap' × 'Erwin Baur') - April 10, and the latest in hybrid 1/38 ('Prima × Cooper 4') - April 16. The weakest growth (trunk cross-section area) had the trees of hybrid 1/21 ('Spartan' × 'Prima') and the strongest the trees of hybrid 1/38. Fruit ripened between September 21 and 25, respectively, for hybrid 1/20 ('Winesap' × 'Erwin Baur') and hybrid 1/36 ('Prima' × 'Cooper 4'). Hybrids 1/23 ('Spartan' × 'Prima') and 1/16 produced the highest average yields (22.8 and 22.7 kg tree^-1, respectively). The fruits of hybrid 1/20 were the largest (197.3 g). Average soluble solids were between 11.7 and 13.6%, total sugars ranged from 6.7 to 7.7% and titratable acids from 0.15 to 0.76%.