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

Abstract

High temperatures and drought are common stresses limiting crop growth and productivity in subtropical regions where citrus are produced. In addition to impacts on physiological processes such as transpiration, photosynthesis, and respiration, excessive solar radiation can also reduce fruit productivity by inducing physiological disorders such as sunburn. This study evaluated the effects of radiation reflectants and anti-transpirants on leaf physiology, and fruit sunburn in grapefruit trees (Citrus x paradisi Macfs. cv. Rio Red) in south Texas during the 2016 and 2017 growing seasons. Two calcium-based reflectants, and a methene/pinolene-based anti-transpirant were foliar applied to fruit-bearing trees. Reflectants reduced fruit and leaf temperatures by 0.2°C and 0.21°C, respectively, while the anti-transpirant treatments increased fruit and leaf temperature by approximately 0.83°C and 0.2°C relative to the controls. Stomatal conductance decreased by 1.3% and 3.3%, respectively, in response to the reflectant treatments, while anti-transpirant treatments resulted in decreased stomatal conductance (8.3%) relative to the controls. More sunburned fruit were found in anti-transpirant treated trees in both years (6% and 8.2% for 2016 and 2017) and the reflectant treatments reduced sunburn incidence by 4.9% and 1.8% in those years. These observations indicate that reflectant applications could be a viable strategy to mitigate heat/radiation stress and sunburn in grapefruit.

Development of a Multipurpose Core Collection of New Promising Iranian Pomegranate (Punica granatum L.) Genotypes Based on Morphological and Pomological Traits

“…Leaf transpiration rate is known to affect calcium and boron absorption and translocation through fruit peel, which is related to diversity of fruit cracking among cultivars [16,40]. In this regard, Rodriguez et al [41] reported that anti-transpiration treatments decreased stomatal conductance and resulted in more sunburned fruit in treated trees.…”

Development and Utilization of a Model System to Evaluate the Potential of Surface Coatings for Protecting Grapes from Volatile Phenols Implicated in Smoke Taint

“…In more recent years, there has been an increase in the application of sunscreen protectants for the protection of crops against extreme heat [ 22 ]. The application of chemical reflectants (i.e., kaolin, calcium carbonate) to fruit can reduce sunburn severity by reflecting UV and IR light [ 23 , 24 , 25 ].…”

Sunburn in Grapes: A Review

“…Chemical reflectants such as kaolin and calcium carbonate (CaCO 3 ) have been trialed with success in different fruit crops. Kaolin [Al 2 Si 2 O 5 (OH) 4 ] is an inert white clay that can reflect UV and IR and reduce FST ( Rodriguez et al, 2019 ). Application of kaolin reduced FST by 1°C and sunburn severity by 12.5%, while fruit quality remained unchanged or even increased ( Brillante et al, 2016 ).…”

“…Results about the effectiveness of these products in viticulture are so far inconclusive. While Fahey and Rogiers (2019) showed that pinolene application was successful in lowering fruit transpiration, Rodriguez et al (2019) showed that FST and sunburn actually increase due to a lack of transpiration. Further, Brillante et al (2016) observed a decrease in fruit quality and consumer preference for the wines made with these products.…”