LINDELL BEACH, B.C. — Rain can be bad news for ripe blueberries.
The precipitation can split the berries’ skin and render them unmarketable.
It is a particular problem in southern highbush and rabbiteye blueberries, and genetics are considered to be the major culprit.
U.S. Department of Agriculture scientists are studying the factors that influence berry splitting and offering guidelines to growers on managing their mature fruit. Their research findings have been published inHortScience.
“Each variety of blueberry has a genetic predisposition for splitting that is inherited from its parents,” said USDA horticulturalist Donna Marshall.
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“The pedigrees of most rabbiteye blueberry cultivars can be traced back to four wild selections: Ethel, Clara, Myers and Black Giant. Thus, they result from a very narrow germplasm base and are highly related.”
Offsprings of these originals include the Tifblue lines, which have a high incidence of splitting, and Homebell lines, which have a low incidence of splitting. From them came the Premier line, whose berries don’t split when exposed to rain.
To understand what happens, the researchers developed a laboratory method to model rain-related splitting. They evaluated water-uptake thresholds in splitting-resistant Premier berries and split-susceptible Tifblue berries at all stages of development.
“Freshly picked berries were submerged in distilled water and left overnight in the lab,” said Marshall.
“Water is absorbed through the stem scar and is distributed throughout the berry over time. (We used) an acridine orange fluorescent dye to penetrate a fruit and encircle the cells.”
She explained splitting is influenced by the cell wall make-up of each berry variety. As water enters the pulp and surrounds the cells, some varieties can attach the water and hold it while other varieties are damaged.
“We think the cell walls are sliding apart, not so much the cells bursting,” she said.
“This is just a theory at the moment. (A graduate student) is working on sectioning the berry and taking pictures of the sections under the microscope. The sections will then be stitched together digitally and produce a very detailed berry.”
Researchers found that Premier absorbs more water than Tifblue yet remains intact and experiences minimal splitting. They concluded that splitting is a cultivar-specific problem.
Financial losses depend on the variety, but the USDA said berry splitting can result in losses of $300 to $500 per acre.
Marshall and her colleagues also investigated the correlation between splitting susceptibility and fruit firmness.
Laboratory and field tests showed that firmer fruit generally has a higher tendency to split. It’s possible that breeders who select for firmness may inadvertently also be selecting for splitting.
However, Marshall said losses are shrinking because growers are more familiar with cultivars that are susceptible to splitting and breeders are replacing them with more resilient ones. As well, producers who grow susceptible plants are becoming more pro-active in their harvesting techniques.
“If the grower has a very good productive cultivar that they know splits, they are very diligent to get it picked before a rainfall,” she said.
“The USDA recently released a new variety that had not been released previously because of its splitting tendencies, yet the growers really like it and it is productive. They just know to pick it before it rains.”
Marshall said the laboratory method of soaking berries and testing for splitting has given breeders a more vigorous and effective screening tool for selecting blueberry varieties.
Plants and berries are rated based on the opinion of the breeder and criteria is subjective. However, it gives breeders an efficient method by which to develop cultivars.
“Our breeder here (in Poplarville, Mississippi) has incorporated it as a standard practice for all of his breeding stock,” she said.
“I have heard from several breeders throughout the country who are also using my technique. Honestly, I never thought that anyone would give it a second thought, but they are. I’m blown away.”
