Observations: Fruit size was not affected by light exposure or tree side, only by the number of fruits, with the low crop load showing the bigger fruit, as expected.
Blush colour was affected differently by the light exposure and tree side.
(cont from last issue)
Crop load did not influence blush colour.
Monitoring of colour development during the season showed that exposed fruit were slightly redder than shaded fruit, but the difference diminished close to harvest.
Tree side did not affect fruit blush colour. Fruit from the west side were slightly redder than fruit from the east side up to early-December, after which fruit showed the same amount of red (Figure 1).
The observed influence of light exposure and tree side on fruit colour could be a combination of a direct effect of light on fruit maturity and the chemical compounds responsible for the red colour.
In fact, fruit maturity was affected by both light exposure and tree side.
Low crop load had an effect on maturity with fruit maturing two days earlier (i.e. to the target IAD = 1.0) than the other two crop loads.
Shaded fruit ripened approximately nine days later than exposed fruit.
Tree side also had an effect on maturity: there was up to two days difference between tree side for the exposed fruit (fruit from the east side was later) while shaded fruit on the west side matured up to five days later and shaded fruit on the east side matured up to 16 days later (Figure 2) than their respective exposed fruit.
Fruit sweetness (°Brix) was slightly affected by light exposure and crop load; the lower crop load generally resulted in sweeter fruit than the other two crop loads, and exposed fruit were sweeter than shaded fruit.
No differences in fruit sweetness were found between fruit from the east and west sides.
The only other noticeable fruit quality difference at harvest was that the exposed fruit were firmer than shaded fruit.
Overall there was a very strong effect of light exposure and tree side on fruit maturity with up to 16 days difference between exposed fruit from the west side and shaded fruit from the east side.
Some effect was also noticed on colour, but this may have been influenced by fruit maturity.
Results
The results from this study suggest that from a practical perspective, to reduce fruit maturity variability (which would also improve fruit sweetness and colour), it would be better to expose fruit (by summer pruning) on the east side of trees earlier than the west side.
Considering that we did not see any sun damage on the fruit it would also be beneficial to reduce fruit shading (assuming similar conditions to this study).
Under conditions where sun damage is an issue, it would be beneficial to generally shade fruit, taking care to reduce shading on the east side to decrease the delay in maturity.
See this article in Tree Fruit June 2020
