2018 ASHS Annual Conference

In the United States, hard cider producers are increasingly interested in acquiring apple genotypes (Malus ´domestica Borkh. and other Malus species) that possess higher concentrations of tannins (polyphenols that taste bitter and/or astringent) and acidity (described as having a sharp taste) than what is typically found in culinary apples. The purpose of this research project was to phenotype a targeted population of genotypes in the United States Department of Agriculture-Plant Genetic Resources Unit (USDA-PGRU) Malus germplasm collection in Geneva, NY for desirable cider apple characteristics. Through a literature search for apples that were historically used in cider production and by the data-mining of the USDA Germplasm Resources Information Network Global (GRIN Global) database, we identified 308 potential candidates of which 180 were characterized in 2017. In the PGRU, each genotype is physically represented by a single-tree accession. Fruit weight (133; 1.34-599 g), diameter (65.6; 31.3-123.3 mm) red peel percent (49.9; 0-100%) or yellow-green background color (2.49; 1-4), flesh firmness (64; 4.5 – 140 N), peel chlorophyll-a (1.04; 0-2.1), and cortex starch pattern index, a 1-8 scale based on potassium iodine staining, (7.73; 3-8) was measured on three 15-apple subsamples from each accession (mean; range of measured values from the sample population is shown in parenthesis). Apple juice was evaluated for: soluble solid concentration (12.3; 2.8- 21.5 °Brix), titratable acidity (4.84; 0.26-22.9 g·L^-1), and polyphenol concentration (1.31; .092-5.14 g·L^-1) (as measured by the Folin-Ciocalteu assay). Sucrose (32.3; 0-107 g·L^-1), glucose (21.0; 3.8-74.4 g·L^-1), fructose (63.1; 11.5-123.0 g·L^-1) and sorbitol (10.4; .288-39.0 g·L^-1) have also been measured on a subset of apple juice samples. As per the Long Ashton Research Station cider apple classification system (> 0.2% (w/v) tannins bitter; > 0.45% (w/v) malic acid is sharp), 29% of the 180 accessions would be classified as bittersweet, 13% as bittersharp, 28% as sweet (neither bitter nor sharp), and 30% as sharp (Folin-Ciocalteu values were corrected to accurately reflect the Lowenthal Permangante Titration assay). These results confirm observations that apples with high polyphenol concentration, particularly those classified as bittersharp, are less common in the germplasm than sweet or sharp apples. Through this research, we hope to identify accessions within the USDA Malus germplasm collection that are of interest to the emerging hard cider industry. Future work will determine the seasonal variability in fruit and juice characteristics, as well as other important features, such as precocity, bearing habit, disease resistance, and overall compatibility with high-density apple orchard systems.