2017 ASHS Annual Conference

American cranberry (Vaccinium macrocarpon) fruit is renowned for its tart flavor. However, most cranberry products contain a considerable amount of added sugar to achieve a desired sugar to acid ratio for palatability. Commercially grown cranberries have an average titratable acidity (TA) of 2.3-3.0% (citric acid equivalents), while Granny Smith, what is considered a tart apple variety, has a TA of about 0.8%. Therefore, one of the selection criteria in Rutger’s cranberry breeding program has been for lower TA, but there is little variability in domesticated varieties for this trait. Two main acids contribute to cranberry fruit’s TA: citric acid which imparts a sour taste and malic acid which imparts a tart taste. Fresh cranberry fruit typically has a malic acid concentration of 6-8 mg/g FW and citric acid concentration of 8-11 mg/g FW. Two unique wild germplasm accessions were identified with reduced TA, resulting from low citric acid and low malic acid levels, respectively. Segregation in crosses indicate that both the low citric and low malic acid traits are independent, recessive, and consistent with single locus Mendelian inheritance. Partial dominance of ‘normal’ alleles is also apparent. Using these selections in our breeding program, we have recovered plants that have a low titratable acidity (0.5-2.0% TA) phenotype, as well as promising fruit quality and horticultural characteristics. A molecular marker was identified within 1cM of the low citric acid locus through a bulk-segregant analysis using simple sequences repeat (SSR) markers. Identification of a molecular marker(s) for the low malic acid locus is underway. These markers will facilitate breeding for lower citric and malic acid phenotypes. With the development of lower acid cranberry cultivars, we can reduce ‘added sugar’ in future cranberry products, allowing for the health benefits of cranberry consumption with reduced caloric intake.