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

‘Kurenainoyume’ is a newly released type 2 red-fleshed apple with pinkish flesh color. In our previous study, we revealed the effects of light condition on red coloration of the skin, flesh, and core of ‘Kurenainoyume’ apple fruit. In this study, we investigated the effects of temperature, shading, defoliation, and crop load on red coloration of the flesh. Low temperature improved flesh coloration; apples subjected to cooling treatment at 5°C or 10°C showed higher a* values of the Lab color space than the control (without cooling treatment), in a temperature-dependent manner. Low temperature reduced the soluble solid content to a lesser extent in some years, whereas fresh weight, malic acid content, and flesh firmness were not affected. Thus, the importance of temperature for flesh coloration was confirmed, similar to its effect on skin coloration. When the trees were covered with cheesecloth with a 50% shading rate from August 1 (82 days after full bloom: DAFB) to October 28 (170 DAFB), flesh coloration was negatively affected, and fresh weight, soluble solid, and malic acid contents were reduced relative to the control treatment (without shading). We also investigated the effects of defoliation (one-seventh of the control) and crop load (two- or threefold the crop load of the normal case control) on flesh coloration. Both defoliation and over crop load also decreased a* values, but their effects on the parameters related to fruit quality were not clear. Because all the treatments of shading, defoliation, and crop load relate to the efficiency of photosynthesis and the distribution of photosynthetic assimilates, our results also demonstrated that photosynthetic assimilates (carbohydrates) were one of the crucial factors affecting flesh coloration.