Fruit & Nut Research & Information Center
Fruit & Nut Research & Information Center
Fruit & Nut Research & Information Center
University of California
Fruit & Nut Research & Information Center

Fruit Quality

Light isn’t just important for leaves – light exposure also affects fruit and nut quality

Light interception by leaves is essential for the growth and survival of fruit trees because it enables plants to convert energy from light into sugar to fuel flowering and fruit growth. Although the green skin of developing fruit can produce sugar via photosynthesis, fruit is primarily a sink, requiring input of supplemental sugars from surrounding leaves. The leaves closest to an individual fruit serve as the primary source and provide the majority of sugars required for development. As a result, leaves immediately adjacent to a fruit have the strongest influence on the composition and size of that specific fruit. It is essential that the leaves closest to developing fruit (in both fruit and nut tree crops) intercept enough light to ensure high quality crop production.

Independent of the nearby leaves, the quality of all tree fruit commonly grown in California improves with exposure to light during development. When fruit are exposed to an optimal amount of light, they achieve higher sugar content, more complex flavor, and deeper color (Figure 5). Since sugar content, flavor, and color are all important components of consumer appeal, fruit tree growers must consider the need for light interception by leaves and fruit when making decisions about how to prune and train their trees.

Although light is necessary for plant survival and fruit production, excessive light and temperature can damage both leaves and fruit. The proteins and enzymes in fruit and nut tree plant cells function best at intermediate temperatures. When temperatures increase above a critical level, often as a result of excessive light exposure, proteins and enzymes begin to break down resulting in cell damage and death. Sunburn results from excessive light interception and heat, which kills photosynthetic tissue and results in low quality fruits and nuts (Figures 6 and 7).

Figure 5a. Pomegranate exposed to sun with consistent deep red rind coloration. Photo courtesy of  J. Moersfelder, USDA Germplasm Repository, Davis CA
Figure 5a. Pomegranate exposed to sun with consistent deep red rind coloration. Photo courtesy of J. Moersfelder, USDA Germplasm Repository, Davis CA
Figure 6. Images of sunburned apple (a), pomegranate (b), peach (c) and walnut (d).
Figure 6. Images of sunburned apple (a), pomegranate (b), peach (c) and walnut (d).

 

 

Figure 5b. A shaded pomegranate with green patches on the rind. Photo courtesy of  J. Moersfelder, USDA Germplasm Repository, Davis CA
Figure 5b. A shaded pomegranate with green patches on the rind. Photo courtesy of J. Moersfelder, USDA Germplasm Repository, Davis CA
Fig. 7. Pomegranate tree with sunburned fruit exposed to excessive light in the outer canopy & healthy fruit in the interior. Photo by J. Moersfelder
Fig. 7. Pomegranate tree with sunburned fruit exposed to excessive light in the outer canopy & healthy fruit in the interior. Photo by J. Moersfelder

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