Thinning and Bagging Treatments and the Growing Region Influence Anthocyanin Accumulation in Red-fleshed Apple Fruit

Abstract

In common apple cultivars with white flesh and red skin, it is known that fruit overload lowers fruit quality, and that skin anthocyanin concentrations are reduced by bagging treatment and warmer climatic conditions. In this study, the effects of these factors on anthocyanin accumulation in the flesh of red-fleshed apples were investigated using 'Geneva' and 'Pink Pearl' apple cultivars. Excess fruiting resulted in decreased anthocyanin concentration in the flesh and the titration acidity of the fruit in both cultivars. Fruit bagging treatments using double-layer paper bags revealed that anthocyanin was synthesized to a certain extent in the flesh under dark conditions in both cultivars. The treatment significantly reduced anthocyanin accumulation in the flesh of bagged 'Geneva' apples compared with unbagged fruit, but no inhibitory effect was clear in 'Pink Pearl' apples. In both cultivars, the anthocyanin concentration in the flesh of unbagged apples grown in sunlight was higher than that in unbagged apples grown in shade, whereas there was no difference between positions for bagged fruit. In apples grown in either sunlight or shade, no significant difference was found between anthocyanin concentrations in the sun-exposed side and shaded side of fruits. These results indicate that sunlight irradiation partially promoted anthocyanin accumulation in the flesh of unbagged 'Geneva' and 'Pink Pearl' apples and accelerated its accumulation on both the sun-exposed and the shaded side. A comparison of the fruit quality of 'Pink Pearl' apples grown in different climatic regions showed that apples harvested at Suzaka, a warmer region, were lower in firmness, starch index, and titration acidity and higher in soluble solids concentration compared with those from Morioka, a cooler region. The anthocyanin concentration in the flesh of 'Pink Pearl' apples from the trees grown at Morioka was more than ten-fold higher than that in apples from the trees grown at Suzaka. Our results suggest that an appropriate fruit load, growth in sunlight, and growth under cooler climatic conditions, may redden the flesh of red-fleshed apples, as is the case for common apples.

Sunlight Differentially Affects the Fruit Skin, Flesh, and Core Coloration of the Type 2 Red-fleshed Apple ‘Kurenainoyume’: Optimization of Fruit Bagging Treatment

“…In addition, cooler climate conditions are advantageous for flesh coloration in 'Kurenainoyume' (Matsumoto et al, 2018b). Honda et al (2014Honda et al ( , 2017 also showed the effect of cooler temperature on the flesh red coloration in 'Pink Pearl'. The practical technique of fruit bagging treatment described in this study has been widely utilized by growers in Aomori Prefecture for several years.…”

“…2C and 4C), but the effect of light on the flesh may be smaller than the skin in both 'Goshogawara' and 'Kurenainoyume'. Honda et al (2017) also reported that sunlight irradiation partially promoted anthocyanin accumulation in the flesh of non-bagging 'Geneva' (type 1) and 'Pink Pearl' (type 2) apples compared with bagging treatment (corresponding to continuous-bagging in our study); although there were differences between the non-bagging control and continuous-bagging in both cultivars with being some year to year variations (Honda et al, 2017). Similarly, red coloration of the flesh of both 'Goshogawara' and 'Kurenainoyume' tended to be light-dependent, but the extent showed year to year variations that were less sensitive than the skin.…”

“…Contrary to skin coloration, environmental factors for flesh coloration of type 2 apple have not yet been fully investigated. Honda et al (2017) reported that sunlight irradiation partially promoted anthocyanin accumulation in the flesh of nonbagging 'Geneva' (type 1) and 'Pink Pearl' (type 2) apples. However, considering the fact that light irradiation, especially UV light, cannot reach deep inside the fruit, it is unclear why sunlight irradiation promotes anthocyanin accumulation in the flesh of type 2 apples, albeit only slightly.…”

Effects of Low Temperature, Shading, Defoliation, and Crop Load on the Flesh Coloration of the Type 2 Red-fleshed Apple ‘Kurenainoyume’

“…Yamane and Shibayama (2006a) recommended the application of trunk girdling to improve the fruit skin red coloration in grapes, and reducing the crop load to concentrate the photosynthetic assimilates to each fruitlet as an important measure to improve the red coloration of the fruit. Honda et al (2017) demonstrated the effects of bagging, temperature, and crop load on flesh coloration in type 2 red-fleshed apple 'Pink Pearl'. However, except for the report by Honda et al (2017), there are no studies that have focused on commercially grown type 2 red-fleshed apple fruit like 'Kurenainoyume' and examined the effects of temperature, shading, defoliation, and crop load on flesh coloration.…”

“…Honda et al (2017) demonstrated the effects of bagging, temperature, and crop load on flesh coloration in type 2 red-fleshed apple 'Pink Pearl'. However, except for the report by Honda et al (2017), there are no studies that have focused on commercially grown type 2 red-fleshed apple fruit like 'Kurenainoyume' and examined the effects of temperature, shading, defoliation, and crop load on flesh coloration.…”