'Kurenainoyume' is a new red-fleshed apple cultivar with a gradually increasing cultivation area. However, cork spot-like physiological disorder (CSPD) of the apple skin has become a serious problem over the years. Therefore, the development of strategies to reduce and prevent CSPD is strongly desired by farmers. To this end, we investigated the effectiveness of i) spraying calcium (Ca), boron (B), or both on the tree and ii) preharvest fruit bagging. Ca or B solutions or both did not decrease CSPD incidence. Furthermore, no relationship was detected between CSPD and the Ca/B content of fruit and leaves, demonstrating that the occurrence of CSPD might not be due to a deficiency in these elements. Pre-harvest fruit bagging reduced the development of CSPD depending on the light permeability of the paper bags used. Moreover, CSPD development was positively correlated with sunshine duration. Therefore, to prevent CSPD, fruit should be covered with light-impermeable paper bags at least from mid-July to late-September because the fruit covered for a shorter period developed CSPD. Thus, we propose that pre-harvest fruit bagging with light impermeable paper could be a useful and practical strategy to reduce or prevent CSPD in 'Kurenainoyume'.

We investigated the effect of fruit bagging treatment using three kinds of paper bags differing in light permeability on the red coloration of skin, flesh, and core in type 2 red-fleshed 'Kurenainoyume' apples by comparison with type 1 'Goshogawara' apples. Skin coloration of both 'Goshogawara' and 'Kurenainoyume' was affected by light and the effect was more marked in 'Kurenainoyume' than 'Goshogawara'. In contrast, the effect of fruit bagging treatment on the red coloration of the core was limited in 'Goshogawara', while core coloration was not observed in 'Kurenainoyume' type 2 apples. Flesh coloration was observed even under dark conditions in both cultivars, and the light tended to enhance the flesh coloration to some extent in both cultivars. Since fruit bagging treatment is a prerequisite for 'Kurenainoyume' to prevent cork spot-like physiological disorder (CSPD) in the skin, we optimized the fruit bagging treatment conditions using a light impermeable double-layered paper bag (2-layer bag), considering both prevention of CSPD and the red coloration of 'Kurenainoyume' skin and flesh. Bag-removal at 25, 35, and 45 days before harvest (DBH), resulted in good skin and flesh coloration without CSPD incidence. Moreover, there was no significant difference in fresh weight, soluble solid, or malic acid contents compared with the non-bagging control. Therefore, we recommend bag-removal from 25 to 45 DBH for 'Kurenainoyume' as a practical cultivation technique.

Background of the study -Following postharvest storage some 'Koukou' apples (Malus × domestica Borkh.) can show unfavorable taste characteristics, in particular low brix values. These apples cannot be distinguished from their normal counterparts based on appearance. Empirically, we inferred that the inclusion of somewhat greener fruits (hereinafter referred to as green 'Koukou' apples in this report) at harvest was a source of this problem. Objective -We aimed to elucidate the reasons behind the development of green 'Koukou' apples, and to show the approaches to reduce such fruit. Methods -We compared the quality of normal and green 'Koukou' apples after harvest during cold storage for 135 days. We determined the positions within the tree canopy in which these green 'Koukou' apples frequently tend to develop. Results -We also found that post-harvest cold storage improved the skin color of green 'Kou-ally distinguish from normal fruit. However, the eating quality of green 'Koukou' apples was inferior to that of normal apples. Additionally, the sucrose content was lower in green 'Koukou' apples than in normal apples. We observed that green 'Koukou' apples were unevenly distributed among the inner and strong branches of the canopy and were more frequently found on the longer bourses and/or bearing shoots. Conclusions -We demonstrated that green 'Koukou' apples were not merely immature fruits but were a kind of physiological disorder retaining green color with low brix values. We suggest that it is important to make the tree vigor low to prevent the production of green 'Koukou' apples. Additionally, the thinning of greener fruit on the strong shoots before harvest may be a viable strategy to reduce the incidence of green fruit. By adopting these approaches, green 'Koukou' apples may be reduced in the marketplace.