By Carla Espinoza Gutiérrez
Prickly blackberries are not only a food safety concern—they can also cause mechanical damage to fruit during harvest and handling. However, thanks to a research team at the University of Arkansas Department of Horticulture, this could soon stop being a thorn in growers’ sides.
Published in March in the G3 Genes|Genomes|Genetics journal, a study identified the specific location or genetic locus of the gene responsible for thorns, a development that could be key for breeders aiming to accelerate the production of thornless cultivars.
Margaret Worthington, associate professor of fruit breeding and genetics with the Arkansas Agricultural Experiment Station and the University of Arkansas, supervised the project. She explains to FreshFruitPortal.com that the marker technology developed in the study is publicly available and no regulatory hurdles should arise for companies interested in implementing it.
“We published the primer sequences and we have shared them with different private companies, even if they don’t have a breeding relationship with us,” Worthington says.
Service providers, including California-based AgBiotech, are already offering assays based on the published markers.
“Kompetitive Allele-Specific PCR (KASP) assays are really nice. You’re looking at maybe $2 to $5 a sample,” she adds. “It is really accessible, and could be synthesized and used in different countries, in public and private programs around the world.”
KASP works as a binary yes/no test. Scientists design a small assay that looks for a specific spot in the DNA, such as the one that controls whether a blackberry plant will have thorns or not. Using colored dyes easily readable by machines, the test then reveals the version in the plant’s DNA: “thorny,” “thornless,” or a mix of both.
The science behind prickle-less blackberries
Blackberry canes with varying degrees of thorns | Photo by student author Carmen Johns.
Researchers focused on the non-prickly trait derived from the cultivar Merton Thornless, a widely used source in fresh-market blackberry breeding programs. They then mapped the trait to a specific locus and developed KASP markers, which are now available to assist breeders in selecting early seedlings.
“Genetic markers are used really widely in row crops to select for things like disease resistance, cutting or flowering date, and other traits of interest,” Worthington adds. “This is the first diagnostic marker for any trait that’s been developed and published in blackberry.”
Until now, breeders have lacked genomic tools to efficiently select for the prickle-less trait. This is because all fresh market blackberry varieties are tetraploids—plants with four copies of each chromosome—making genetic mapping more complex.
However, this type of development comes with risks. There are concerns over potential co-selection of undesirable traits, meaning that detrimental characteristics, such as high acidity or poor cold tolerance, could be carried over to the resulting breed along with the thornless trait.
Worthington says that these traits are already prevalent in current thornless genetic material. “For me, it’s more about being able to introduce new, interesting diversity, and hopefully improve those traits in the region without bringing back thorniness.”
No more prickly business
To identify the genetic markers responsible for thorns, the research team used genome-wide association analysis on 374 thorned and thornless blackberry varieties. The study identified a cluster of genetic markers on chromosome Ra04, which growers can now use to screen seedlings through genotyping before field trials.
Ellen Thompson, global director of breeding at Hortifrut, and co-author of the paper, said the markers will allow the firm’s breeding program—which is already fully thornless—to introduce some genetic diversity.
“Using these markers to screen seedlings in a high-throughput manner allows us to incorporate diverse and rustic traits of thorny germplasm, study segregation ratios more quickly, and identify the associated desirable prickle-free phenotypes at a very early stage,” she says.
Worthington notes that while the team identified the locus, they’ve not yet found the specific causal gene responsible for the thornless trait. Future research will aim to isolate that specific gene.
*All photos courtesy of Margaret Worthington.
Related articles:
U.S. raspberry and blackberry market to continue growth trend the next 10 years
Decoding blackberry DNA: UF study paves way for enhanced breeding strategies and better berries for Florida