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United States Department of Agriculture

Agricultural Research Service

Research Project: INTEGRATED ORCHARD MANAGEMENT AND AUTOMATION FOR DECIDUOUS TREE FRUIT PRODUCTION

Location: Appalachian Fruit Research Laboratory: Innovative Fruit Production, Improvement and Protection

Title: Photosynthetically active radiation (PAR) x ultraviolet radiation (UV) interact to initiate solar injury in apple

Authors
item Glenn, D Michael
item Yuri, Jose Antonio -

Research conducted cooperatively with:
item

Submitted to: Scientia Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 26, 2013
Publication Date: August 19, 2103
Citation: Glenn, D.M., Yuri, J. 2103. Photosynthetically active radiation (PAR) x ultraviolet radiation (UV) interact to initiate solar injury in apple. Scientia Horticulturae. p. 105-110.

Interpretive Summary: Sunburn or solar injury (SI) in apple is associated with high temperature, high visible (PAR) and ultraviolet (UV) radiation, and can result in as much as 50 percent crop loss in some years. While a fruit surface temperature (FST) of 40 degrees C has been established as critical level initiating SI, visible and UV thresholds have not been established. Reduction in fruit peel quantum efficiency (Fv/Fm) is a sensitive indicator of damage prior to visual SI symptoms. The objectives of the present study were to: 1) use PAR and UV filters to develop a range of PAR and UV levels that lead to reduced Fv/Fm in apple peel, 2) identify levels of FST, PAR, and UV that exceed the ability of five apple cultivars to fully recover after 24 h, and 3) measure the effect of varying levels of FST, PAR, and UV on Fv/Fm alone and in combination to identify interactions affecting Fv/Fm in recovery as guidance in evaluating SI prevention technology. It appears that threshold values for initial damage to Fv/Fm are not easily defined. Cultivar differences and annual variation have a strong influence on the sensitivity of the peel to FST and radiation levels. We demonstrated that ‘Granny Smith’ fruit peel is more tolerant to FST, UV, and PAR stresses than ‘Gala’. Cultivars also vary in the response to FST, UV, and PAR, and with the level of maturity. The PAR x UV interactions are complex and also include the acclimation of the cultivar but in the prevention of SI, reducing FST, PAR, and UV simultaneously is likely the most effective strategy.

Technical Abstract: Sunburn or solar injury (SI) in apple is associated with high temperature, high visible light and ultraviolet radiation (UV). Fruit surface temperature (FST) thresholds for SI related disorders have been developed but there are no thresholds established for solar radiation. The objectives of the study were to: 1) use photosynthetically active radiation (PAR) and UV filters to develop a range of PAR and UV levels that lead to reduced Fv/Fm in apple peel, 2) identify levels of FST, PAR, and UV that exceed the ability of five apple cultivars to fully recover after 24 h, and 3) measure the effect of different levels of FST, PAR, and UV on Fv/Fm alone and in combination to identify interactions affecting Fv/Fm recovery to serve as a guideline in evaluating SI-prevention technology. The variable transmission of UVb, UVa, PAR, and NIR through films of Surround and Raynox provided a wide range of radiation levels at the fruit surface to model the quantum efficiency (Fv/Fm) of photosystem II (PSII) in growth chamber and greenhouse studies. Increasing UV and PAR reduced Fv/Fm the greatest amount in ‘Gala’, while ‘Granny Smith’ had the least reduction suggesting that PSII in ‘Granny Smith’ has higher UV and PAR tolerance. All cultivars except ‘Fuji’ at harvest had some interaction component of PAR and UV that decreased Fv/Fm compared to untreated control fruit as both PAR and UV increased. When re-exposure was conducted on the 5 cultivars, Fv/Fm further decreased with the cumulative PAR and UV despite having a period of dark recovery between each 24 h exposure. Cultivar differences have a strong influence on the sensitivity of the peel to FST and radiation levels. Cultivars differ in their response to FST, UV, and PAR as they mature and also exhibit year-to-year variation. This inconsistency suggests that acclimation to the environment also varies between years. PAR x UV interactions are complex and include the acclimation of the cultivar to the stress but in the prevention of SI, reducing FST, PAR, and UV simultaneously is likely the most effective strategy.

Last Modified: 8/30/2014
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