The Barren Berry phenotype: untangling cranberry (Vaccinium macrocarpon Ait.) genetic contamination in central Wisconsin and beyond

Wisconsin is the world’s leading producer of cranberries (Vaccinium macrocarpon Ait.; 2n = 2x = 24). The state produces over twenty-thousand acres that contribute to more than 50% of the global total production, with more than one billion dollars in value. Cranberry growers in the “central sands” of Wisconsin have been experiencing yield decline due to vegetative unproductive genotypes, popularly known as “Barren Berry’’, which consistently remain vegetative and produce no fruit. The purpose of this study was to compare visual inspection in the field to DNA fingerprinting for the early detection of unproductive/barren genotypes. Additionally, the study served as a survey of unproductive genotypes in central Wisconsin, the largest growing region in the world. A total of 839 cranberry leaf samples, from 14 growers representing plantings to four cultivated varieties, were submitted for DNA testing of two visually determined phenotypes: unproductive or barren (n = 646; those that produced little to no fruit), versus productive or fruiting (n = 193). We conducted genetic fingerprinting on the leaf tissue using nine microsatellite markers previously shown to differentiate cranberry genotypes. This study identified a barren berry genotype unique to central Wisconsin, which we denoted “Barren Berry 1”. This genotype accounted for 43% of samples submitted as the barren berry phenotype. Genetic fingerprinting revealed sixty-five different genotypes in beds which were thought to be monocultures of just four cultivated genotypes. Early detection of genetic contamination through visual inspection, genetic testing, and responsible propagation can drastically aid in the management and longevity of cranberry beds, and in turn save time and money to the growers.