Correlation between phenolic content and antioxidant activity in fruits of Prunus avium infected with Monilia laxa

Abstract

Accumulation of phenolic polymers reinforce plant cell walls, limiting fungal penetration. Some of these compounds, such as isochlorogenic acid, are particularly active in limiting fungal extension. Two main features of phenolic compounds are that they are produced in greater quantities by resistant plant genotypes, and that they have the ability to limit plant pathogens growth. Thus, they could be considered as potential markers of resistance to Monilinia laxa in sweet cherrie breeding programs. We investigated the content of the total phenols (TP), total tannins (TT) and anthocyanins (A) in the fruits of ten sweet cherrie cultivars, before and after the infection with M. laxa, under the field conditions. In addition to this, we determined the total antioxidant capacity of the fruit extracts using the DPPH-free radical scavenging assay and FRAP method. The correlations between phenolic classes and antioxidant activity have been calculated, as well. Results showed that the TP content ranged from 3.71 to 7.52 mg gallic acid equivalent (GAE) g-1 dry weight depending on the genotype and the infection. TT content was lower and it ranged from 0.52 to 2.64 mg GAE g-1 dry weight. Anthocyanins content ranged from 0.29 to 2.71 mg cyanidin-3-glucoside g-1 dry weight. DPPH values ranged from 38.47 to 63.50 % of neutralised radicals, while FRAPvalues were 14.73-33.69 mg trolox g-1 fresh weight. No positive correlation was found for antioxidant tests and phenolic compounds investigated. Still, TP and TT were higher in infected fruits of five specimen (Junska rana, Summit, Mershant, Priusodebnaja and Burlat), and A levels were higher in the same cultivars except for the cv. Summit. These cultivars accumulate defensive compounds under the pathogen induced stress and may be considered as more tolerant genotypes with more desired traits for production, selection and breeding programmes.