Bourse Length Distribution and Return Bloom of Four Apple Cultivars

Factors that affect flower induction in bourse buds are critically important for consistent production of apples. Irregular flowering may lead to inconsistent cropping (biennial bearing) which is a huge challenge for the apple industry. In order to further understand the factors that can exacerbate biennial bearing, this study was conducted to determine the optimum bourse length for flower induction in four apple cultivars. Bourse lengths of two biennial bearing cultivars (Honeycrisp and Golden Delicious) and two regular bearing cultivars (Gala and GoldRush) were measured throughout the growing season. Half the measured spurs were defruited at bloom and half carried a single fruit. Among the four apple cultivars, a wide range in bourse length distribution was measured. Both Honeycrisp, and Gala had the highest return bloom on bourse buds 0.5 - 2.5 cm long. Golden Delicious had the most return bloom distributed on bourses 0.51-2.0 cm long while Gold Rush had most return bloom distributed on bourses 0.51 – 2.5 cm in length. Among the 4 apple cultivars, Gala had the highest return bloom (92% on de-fruited and 60% on single fruited spurs) while Honeycrip had the least amount of return bloom (17% on de-fruited and 3.5% on single fruited spurs). Golden Delicious and GoldRush were intermediate in their level of return bloom with 33% for de-fruited treatment and 16% in single fruited of Golden delicious and 40% and 7% in single fruited spurs of GoldRush.