Effect of natural light on the phenolic compounds contents and coloration in the peel of ‘Xiyanghong’ (Pyrus bretschneideri×Pyrus communis)

Abstract

Pear (Pyrus) is one of the most important fruit trees in the world. As an important pear cultivar, ‘Xiyanghong’ (P. bretschneideri × P. communis) is widely cultivated. However, its red skin is commonly occurred in the light exposed part, which restrictes its commercial value. Here, to investigate the effect of natural light on coloration and the phenolic compounds of the ‘Xiyanghong’ peel, the bag surface of bagged pears was cut to expose the peel to natural light, and exposed peel versus bagged peel were compared. The results showed that the exposed peel started to be colored in red at 57 days after full bloom (DAFB) and kept in red until the final stage, while the bagged peel was not colored among all stages. Anthocyanin content of exposed skin was significantly higher than that of bagged skin at the 57 DAFB and the following two stages. This similar higher level in exposed skin was also observed in the contents of other five phenolic compounds, including syringic acid, gallic acid, procyanidin B2, quercetin-3-galactoside, and quercetin-3-rutinoside. In addition, the expression of pathway genes, PAL, CHS, CHI, F3H, DFR, ANS, and UFGT, correlated highly with anthocyanin accumulation. And the expression of regulative genes MYB10, bHLH3, and light response gene HY5 were also with a consistent trend at 57 DAFB. These results will contribute to an improved understanding of the mechanism of red pears response for light, and will aid development of new cultivation techniques to improve coloration and quality of pear.