Prevention of New Cork Spot-like Physiological Disorder in ‘Kurenainoyume’ Apples by Pre-harvest Fruit Bagging

‘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) pre-harvest 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’.