S11 - Session P5 - Risk reduction measures against sunburn incidences in apple: covering individual on-tree fruit with shading materials

Authors: Chikako Honda *, Kenichi Matsuda, Hariya Nakagawa, Katsuaki Ohshiro, Yoshikazu Fujita, Hisataka Mizuno, Tadashi Ito, Hidekazu Ogawa, Hiroshi Iwanami

Sunburn of apple fruit occurs when the surface temperature of the fruit exceeds a certain level or when the fruit is exposed to sunlight. To prevent sunburn of apple fruit, the effect of the use of shading materials on the incidence of sunburn of apple fruit was investigated at four sites in Japan (Kanazawa, Uozu, Suzaka, and Morioka) with different temperatures for two years, 2016 and 2017. From late June to mid-July, the fruits on the trees in sunny locations were covered with 100 % white shading material made of woven fabric (WF) or knitted fabric (KF), and the shading materials were removed prior to harvest to minimize negative effects on the red coloring of the fruit. Covering reduced the percentage of sunburned fruit in 'Tsugaru' in Suzaka and Morioka, 'Shusei' in Kanazawa, and 'Fuji' in Uozu. The degree of the mitigation effect varied among locations and cultivars. Fruit skin color (red and ground color) and internal fruit quality (firmness, starch index, soluble solid content and titration acidity) were not substantially affected by covering. The long-term use of the shading materials, incidentally, increased the probability of disordered fruit. Therefore, the shading materials should be removed from the fruit on the tree as soon as the period of risk of sunburn has passed. Overall, the method of covering the fruit on the tree with these materials can be considered as one of the options to reduce the risk of sunburn occurrence on apple fruit.