Rain-related splitting is a detriment to commercial blueberry growers in the southeastern United States. This problem has been reported to have reduced marketable yields and thus profit for these growers by up to 20% (Marshall et al., 2006). Researchers have been working on the problem of fruit splitting in various fruit crops for more than 70 years. If a few key factors that contribute to splitting in blueberries can be identified and implemented as screening tools for new cultivars, then long-term reductions in commercial blueberry fruit splitting are feasible.
Blueberries absorb external water either through the peel or through the pedicel. Yet some blueberry cultivars tend to absorb more water than the berry can sustain, thus resulting in fruit splitting. Studies have suggested many factors that influence fruit splitting. These factors include cultivar, fruit maturity, temperature of water (fruit splitting increases with an increase in water temperature), fruit temperature, period of wetting, soluble solids content, fruit firmness and turgor, relative humidity, soil moisture, peel permeability, and elasticity of the peel (Ackley and Krueger, 1980; Bullock, 1952; Gerhardt et al., 1945; Marshall, 1954; Powers and Bollen, 1947; Zielinski, 1964). It is generally agreed (Ackley and Krueger, 1980; Andersen and Richardson, 1982; Bullock, 1952; Davenport et al., 1972; Marshall, 1954) that the cause of cracking in cherries, whether directly or indirectly, is absorption of external water through the fruit peel. Therefore, protecting fruit from rainwater contacting and remaining on the fruit should reduce or eliminate splitting. However, Marshall (2001) found that covering blueberry plants to prevent rainfall from contacting the fruit was not sufficient to eliminate splitting. After a rainfall, split berries were harvested from both uncovered as well as covered plants. As expected, plants had significantly more split berries if left uncovered (30.40%) than did covered plants (19.90%). Yet some splits apparently occurred from uptake of water by the roots that is transported to the fruit by the xylem.
Susceptibility to splitting in cherries appears to be related to the rate and quantity of water uptake by the fruit (Belman and Keulemans, 1996). Uptake of water into the fruit occurs not only through the pedicel, but also through the peel. Lane et al. (2000) found that split-resistant cherry cultivars absorbed more water before splitting than did split-susceptible cherries. They concluded that water uptake thresholds at which fruit split was a major factor explaining the split susceptibility difference in cherry cultivars. Lane et al. (2000) added that a cultivar difference causally related to splitting susceptibility could be attributed to the amount of air-filled spaces between cells, which would allow water to be taken in without increasing fruit volume. This could be determined by measuring the ratio of percent water uptake to volume increase of resistant and susceptible cultivars. Ratios found to be similar suggest that cell adhesion might be an explanation for cultivar difference. Cultivars with cells weakly adhering to each other may split at lower turgor pressure than those with cells that strongly adhere.
A mature planting (30 plants of each cultivar) of ‘Tifblue’ and ‘Premier’ plants located at the Thad Cochran Southern Horticultural Laboratory in Poplarville, MS, was used for this study. Plants were divided into four replications of four plants/replication ‘Tifblue’ is a split-susceptible (SS) rabbiteye cultivar and ‘Premier’ is a split-resistant (SR) rabbiteye cultivar.
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Marshall, D.A. , Spiers, J.M. , Stringer, S.J. & Curry, K.J. 2007 Laboratory method to estimate rain-induced splitting in cultivated blueberries HortScience 42 1551 1553
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