First Published Blackberry Genetic Marker Paves Way for Speedier Variety Development

The Problem

Thorns on blackberry canes can scratch pickers and damage fruit, making thornless varieties the preferred option. However, blackberry breeders have not had the genetic information explaining why some plants lacked thorns. Making the genetic analysis more complex is the fact that cultivated blackberries are tetraploids, meaning they possess four copies of each chromosome. With no previously published diagnostic markers for any traits developed and published in blackberries, researchers considered finding the genetic locus, or the location of a gene on a chromosome, an obvious target.

The Work

Margaret Worthington, an Associate Professor of Fruit Breeding and Genetics for the Arkansas Agricultural Experiment Station, led a collaborative effort to identify the genetic locus for thornlessness. Using a genome-wide association study, they analyzed DNA from 374 blackberry varieties to locate genetic variations linked to the trait. These DNA samples were analyzed through genotyping, a highly precise process that involves scanning for and identifying variations in the genetic code that could influence the prickly trait. The study identified variations, known as single-nucleotide polymorphisms or genetic “markers,” that pinpoint the region associated with thornlessness.

The Results

The research identified the first known genetic locus controlling thorn development in blackberries. The genetic markers give breeders the ability to screen seedlings at the DNA level, which saves breeders time and effort. The work also revealed that the thornless trait resides in a linkage disequilibrium block, or a region where genetic markers are more likely to be inherited together than by happenstance. Thus, the thornless trait is often passed on from parent plant to child plant along with other genes, including undesirable traits like high acidity and cold intolerance. This suggests that consistently selecting for the thornless trait has reduced genetic variation around the locus.

The Value

This research represents the world’s first publicly available markers for blackberries. For blackberry breeders, knowing the genetic locus for thornlessness provides a new tool for developing better blackberry varieties more efficiently. The ability to screen for thornlessness at the seedling stage can reduce breeding cycle times. Additionally, the increased genetic understanding of thornlessness suggests that conducting crosses with thorny plants could help increase genetic variation around the locus.