Risk reduction measures against sunburn incidences in apples: covering individual on-tree fruit with shading materials

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

XXXI International Horticultural Congress (IHC2022): International Symposium on Adaptation of Horticultural Plants to Abiotic Stresses

C. Honda, K. Matsuda, H. Nakagawa, K. Ohshiro, Y. Fujita, H. Mizuno, T. Ito, H. Ogawa, H. Iwanami

apple, fruit disorders, shading materials, sunburn

https://doi.org/10.17660/ActaHortic.2023.1372.30