Exogenous onion extract hastens bud break, positively alters enzyme activity, hormone, amino acids and phenol contents, and improves fruit quality in ‘Anna’ apple trees

•“Anna” apple bud break% maximized with onion extracts (OEs).•OEs hastened bud break and shortened flowering time.•Bud chemical composition positively altered, in favor of bud break, by OEs.•OEs application could be an important tool for bud break and for fruit quality.

Metabolic changes in the activity of catalase, and the contents of hydrogen peroxide, proline, total free amino acids, total indoles, anthocyanins and free phenols in floral buds of apple (Malus domestica Borkh. cv. ‘Anna’) trees were investigated during dormancy and bud break under the effect of foliar application of two onion extract rates (100 and 200 ml l−1). Flowering percentage, fruit yield characteristics (i.e., fruit-set, number of fruits tree−1 and fruit yield tree−1) and fruit quality measurements were increased, while number of days recorded to reach full bloom were reduced with the application of both onion extract rates. In addition, contents of hydrogen peroxide, proline, total free amino acids, total indoles and anthocyanin were significantly increased in floral buds, particularly during bud break. In contrast, the activity of catalase and the content of free phenols were reduced. The best results were obtained from the extract rate of 200 ml l−1 that could be recommended for early and high percentage of flowering and increased yield with high quality by regulating the metabolism of amino acids, including proline and indoles, and the activities of catalase and hydrogen peroxide in apple floral buds.