Cultivars of Rubus subgenus Rubus lacking prickles are highly favored by cultivators, primarily owing to considerations of food and labor safety, and the prevention of mechanical damage to the fruit caused by these spiny protrusions.
The research team, led by Johns, pinpointed a singular genetic locus that governs the development of prickle-free stems. Image attribution: Gerardo Antonio Romero.
Blackberry cultivation represents a niche agricultural sector, progressively augmenting its market share within the fresh berry segment.
The escalating consumer demand, coupled with mounting cultivation expenses, necessitates the development of varieties that exhibit adaptability across diverse environmental conditions and are amenable to various agronomic management practices.
Prickles present a significant impediment to blackberry production systems, posing risks to food safety and leading to mechanical deterioration of the fruit, thereby diminishing its post-harvest longevity.
A principal objective within fresh-market blackberry breeding initiatives is the release of cultivars devoid of thorns, or more precisely, prickles, as these terms are frequently employed interchangeably in relevant literature.
Botanically, prickles are distinguished from thorns and spines, originating from cortical and epidermal cellular tissues.
“Blackberry breeders have historically lacked the requisite genetic insights to comprehend the mechanisms underlying the absence of what are technically termed prickles, though colloquially referred to as thorns,” stated Dr. Margaret Worthington, a researcher affiliated with the Arkansas Agricultural Experiment Station.
“All commercially viable fresh-market blackberry varieties are tetraploids, meaning they possess four sets of each chromosome, in contrast to the two sets found in human genetics.”
“This augmented chromosome count renders genetic analysis considerably more intricate.”
“The specific genetic locus, which denotes the chromosomal position of a gene, responsible for the prickly characteristic remained unidentified, presenting a clear avenue for research.”
The findings generated by the research consortium represent the inaugural diagnostic marker for any trait within the blackberry species that has been successfully developed and disseminated.
“These represent the world’s first publicly accessible genetic markers created for both fresh-market and processing blackberry varieties,” commented Dr. Ellen Thompson, Global Rubus Breeding and Development Director at Hortifrut Genetics.
“The utilization of such markers expedites the breeding process and reduces associated costs, enabling plant breeders to make informed selection decisions at an earlier stage, prior to the transplantation of seedlings into cultivation fields.”
The research team employed a genome-wide association study methodology to ascertain the genetic locus responsible for the thornless attribute.
A total of 374 distinct blackberry varieties, encompassing both prickly and prickle-free specimens, were sampled for their genetic material.
Subsequent analysis of these DNA samples involved genotyping, a sophisticated procedure that meticulously scans for and identifies variations within the genetic code that may influence the development of prickles.
Should such variations, identified as single-nucleotide polymorphisms (SNPs), exhibit a statistically significant correlation with the trait, it strongly suggests that a gene situated within that chromosomal region plays a role in its expression.
These SNPs, also referred to as genetic markers, serve as indicators pointing to the specific chromosomal area associated with the trait under investigation.
“The application of genetic markers is a more recent development in the field of blackberries and raspberries, whereas this approach is considerably more advanced in staple crops such as rice and soybeans,” Dr. Worthington observed.
“Genetic markers are extensively utilized in row crops for the selection of desirable traits, including resistance to diseases, optimized cutting or flowering times, and other characteristics of commercial importance.”
A further significant revelation from the study was the limited genetic diversity observed in the vicinity of chromosome Ra04, leading to the formation of a linkage disequilibrium block—a chromosomal segment where genetic markers tend to be co-inherited with a higher probability than random chance.
Consequently, for the gene conferring thornlessness within this block, it is often transmitted from parent to offspring alongside numerous other genes, potentially introducing undesirable traits such as elevated acidity, susceptibility to cold, and non-erect stem growth requiring physical support.
“Intense selection for thornless plants has inadvertently introduced these detrimental characteristics, resulting in a reduction of genetic variation surrounding the locus,” Dr. Worthington elaborated.
“Reintroducing genetic diversity through crosses with prickly plant varieties could potentially mitigate this issue.”
The research findings were formally documented in a publication within the esteemed scientific journal, G3: Genes, Genomes, Genetics.
_____
Carmen A. Johns et al. Genetic control of prickles in tetraploid blackberry. G3: Genes, Genomes, Genetics, published online March 20, 2025; doi: 10.1093/g3journal/jkaf065
