Triterpenic acid content in the fruit peel of Malus × domestica Borkh. depends on the growing technology

Abstract

Regardless of the numerous investigations of secondary metabolites, the impact of new growing technologies or individual technological means on fruit internal quality, particularly triterpene concentration in apple fruits has not been studied yet. Apple-tree (Malus × domestica Borkh.) growing technologies and geographical location of the growing site had clear effect on triterpene concentration in apple fruits. The effect of crop load, fruit location in apple-tree canopy, planting distance, apple-tree vegetative growth regulation and geographical location on triterpene content in apples was evaluated in 2015 and 2016. Four triterpenic compounds: corosolic, betulinic, oleonolic and ursolic acids, were quantified in apple peel. Triterpene accumulation in apple fruits was directly correlated with crop load, where 17% more total triterpenes were found at the highest crop load (12 fruits cm-2 trunk cross-sectional area (TCSA)) in comparison to the lowest crop load (4 fruits cm-2 TCSA). Higher concentration of triterpenes was found in the fruits harvested from the inner canopy of the apple-tree. Apple-tree growth regulation affected the synthesis of triterpenes – trunk incision decreased the amount of total triterpenes by 16% compared to the control and by 26% compared to summer pruning. Also, a trend of higher accumulation of triterpenes in fruits was found along with decreasing apple-tree planting distances. Colder climate and shorter vegetation period resulted in significantly higher contents of triterpenes in the fruits of cultivar ‘Auksis’ in Lithuania and Estonia compared to the fruits grown in Poland. The same trend, yet insignificant, was noticed for the cultivar ‘Ligol’.