Comparison of Paper Bags, Calcium Carbonate, and Shade Nets for Sunscald Protection in ‘Murcott’ Tangor Fruit

Abstract

<jats:p>‘Murcott’ tangor (<jats:italic>Citrus reticulata</jats:italic> × <jats:italic>Citrus sinensis</jats:italic>) is susceptible to sunscald injury due to high temperatures during summer in Chiayi, Taiwan. The average rate of sunscald damage in ‘Murcott’ tangor fruit is 13.6% when no protective measures are used. The objective of this study was to compare the effects of covering developing fruit with white paper bags, calcium carbonate, or shade nets to reduce the effects of sunscald. A significant reduction in sunscald was realized when using white paper bags, calcium carbonate spray, or white, green, and black shading nets. Calcium carbonate spraying was the most rapid method, but was less effective in controlling sunscald, and resulted in the lowest photosynthetic rate. Compared with trees under shade nets, those under black netting had larger and heavier fruit. There were no significant differences in peel color, titratable acid (TA), total soluble solids/titratable acid (TSS/TA) ratio, or respiration rate for the evaluated treatments. Although all shading materials reduced sunscald, the use of shade net was the most effective in controlling damage related to this, and thus can have significant benefits for commercial citrus (<jats:italic>Citrus</jats:italic> sp.) orchard operations.</jats:p>

Physiological Effects of Exogenously Applied Reflectants and Anti-Transpirants on Leaf Temperature and Fruit Sunburn in Citrus

“…In contrast to our results, a study by Abdallah (2019) [46] showed that AT treatments had no significant effect on the sunburn of tomato. This is similar to the results found by Tsai et al (2013) [10], who found low rates of sunscald in treatments containing calcium carbonate (CaCO 3 ) as well as low leaf temperatures, and a low net photosynthetic rate due to particles inhibiting gas exchange.…”

“…Sunburn in citrus fruit has been a common physiological issue facing growers and causes financial losses each year [1]. Studies on sunburn and water stress management include the application of foliar sprays with inert reflective materials such as kaolinite clay [5][6][7], anti-transpirants, evaporative cooling systems [8,9], and protecting fruit with paper bags to reduce the appearance of sunscald [2,10]. Kaolin treatment has been used for sunburn reduction with some success on apples [11], grapefruit [12], and pomegranates [13].…”

“…Washington State produces over half of the apple crop in the United States, yet sunburn causes serious economic losses averaging over 10% annually [9]. In Australia, sunburn causes 40-50% of losses for sensitive apple cultivars [14] and in Taiwan, 'Murcott' tangerines and some early clementine mandarins are susceptible to sunburn, causing 13.6% of losses [10]. In most of these regions, few or no mitigation practices are currently in place to prevent fruit losses due to sunburn.…”

“…In apples, sunburn disrupts the structure and morphology of the fruit, alters pigment composition, and decreases photosynthesis, which results in decreased fruit quality. Similarly, in citrus fruits, sunburn alters photosynthetic systems and ruptures oil glands, leading to subsequent water loss and reductions in growth and yield [10,17]. The combination of high irradiance and high temperatures causes the formation of highly reactive and hazardous active oxygen species (AOS) in plant tissue [18,19].…”

Sunburn in Grapes: A Review

“…Fruit bagging is often used to produce high-quality table grapes, enabling a good and homogenous coloration, aromatic quality, and protection against grape berry moth and sunburn ( Karajeh, 2018 ). Paper bags have been cited as being as effective as dark nets in reducing sunburn ( Tsai et al, 2013 ); they reduce the temperature inside the bag and block direct sunlight, which makes them effective against both SB and SN. The efficiency of bags depends on the color and material, as several options exist.…”