Effect of apple-tree vegetative growth regulation on accumulation of fruit triterpenic and phenolic compounds

Abstract

Introduction Tree growth regulation, such as spraying trees with growth regulator Regalis™ or summer pruning, is common practise in commercial orchards, but fruit quality is mostly determined by external quality parameters (fruit colour, size, firmness) and basic internal quality parameters, such as soluble solids, sugar content, acidity, etc. However, there is limited research data evaluating bioactive compounds, such as phenolics or triterpenes, in relation to tree growth regulation. In this work, we evaluated regulation methods of apple-tree vegetative growth and their impact on accumulation of bioactive compounds. Materials and methods This study was carried with apple cultivar ‘Rubin’ on rootstock P 60 planted at the distance 4 x 1,5 m. Four treatments of tree vegetative growth control were established: 1) Control; 2) Tree trunk incision before flowering by chain saw; 3) Application of growth regulator ‘Regalis’ (prohexadione-calcium) at the rate 2,5 kg ha-1 immediately after the flowering; 4) Summer pruning performed in the middle of August. All measurements are conducted by appropriate HPLC methods. Results In control samples, apples accumulated 12,677 mg g-1 DW of triterpenic compounds, whereas trunk incision significantly reduced triterpene concentration to 10,853 mg g- 1 DW, while summer pruning had the opposite effect – apples accumulated significantly higher content of triterpenes (13,727 mg g-1 DW). Growth regulator Regalis™ did not had impact on triterpene concentration in apples. Control apples accumulated 1,729 mg g-1 DW of phenolic compounds. Trunk incision didn’t had impact on change in phenolics (1,878 mg g-1 DW). Summer pruning significantly increased phenolics in apples (1,905 mg g-1 DW), whereas the use of Regalis™ had drastic decrease of phenols to 1,307 mg g-1 DW. Conclusions Summer pruning significantly increased both triterpenic and phenolic compound content in apples. Growth regulator Regalis™ si gnificantly dec