2019 ASHS Annual Conference

Fruit sunburn accounts for approximately 14% of losses in mandarins, up to 40% in apples, and 10-15% in other fruit crops. Sunburned fruit is discolored and exhibits varying degrees of necrotic tissue which reduces fruit quality and marketability. Sunburn occurs on the surface of fruits and are associated with the rupture of glands, phytotoxic injury to tissues and subsequent water loss. Sunburn development is correlated with rising ambient temperatures, high solar radiation, along with other environmental conditions which can cause stress to plants by impacting transpiration, photosynthesis. The degradation of chlorophyll is a major indicator of sunburn damage in fruits. When this occurs, photosystem I and II are affected by high temperatures that disrupt the content and pigmentation of chlorophyll-carotenoid complexes and alter membrane lipids that help prevent photoreduction. Another consequence of high intensities of UV-radiation and temperatures is the development of free radicals in plant tissue. Highly reactive radicals cause damage to the membrane integrity leading to cell death. However, sunburn and the physiological effects it has on fruit tissues have not been studied extensively in grapefruit. Furthermore, very little is known about the changes in peel and juice physiochemistry when fruit are subjected to sunburn. To better understand the role of chlorophylls and other stress response compounds in grapefruit sunburn development (or lack thereof), sunburned and non-sunburned fruit were collected and analyzed for physical properties, chlorophylls, carotenoids, and proline in two consecutive years. We found that there was a significant, positive relationship between chlorophyll B and sunburn severity. Additionally, we found that sunburned fruit had lower proline concentrations and the more severe the incidence of sunburn, the lower the proline concentration. However, total chlorophylls, chlorophyll A, and carotenoids were not significantly affected by sunburn.