The 2012 ASHS Annual Conference

Marker-assisted breeding is facilitated by marker-locus-trait associations validated in germplasm relevant to a particular breeding program. Establishing these associations depends on having an extensive, reliable phenotype database for traits of interest in this germplasm. A reference germplasm set of 496 individuals including cultivars, selections, and seedlings was identified as part of the USDA-SCRI RosBREED project. The germplasm set provides allelic representation of historic and current parents in RosBREED demonstration apple breeding programs at Cornell University, Washington State University, and the University of Minnesota. Phenotyping at the three locations was conducted according to standardized protocols that specified fruit harvest maturity and focused primarily on fruit traits evaluated at harvest and following 10 and 20 weeks of refrigerated storage. Phenotypic data were collected for the sensory texture traits of firmness, crispness, and juiciness, as well as instrumental texture measures using the Mohr^® Digi-Test (Washington State University and University of Minnesota) and Effegi penetrometers (Cornell University). In 2010 and 2011, fruit from 215 and 330 individuals were harvested, respectively, and a total of 367 individuals were evaluated over the two years . As each location had a largely unique set of individuals as well as differing environmental conditions, means, ranges, and phenotypic variances for traits varied greatly among locations for some traits. For example, the mean ±se for the Digi-Test firmness measure M1 at harvest in University of Minnesota reference germplasm was 74.0 ± 2.3 N (2010) and 73.0 ± 1.2 N (2011)  compared to 78.8 ± 1.3 N (2010) and 80.6 ± 1.2 N (2011) for that of  Washington State University. Year-to-year repeatability of traits at a location was generally low to moderate with Pearson’s correlation coefficients ranging from 0.14 to 0.48 for sensory crispness, 0.30 to 0.42 for sensory firmness, and 0.37 to 0.54 for Digi-Test Cn (a measure of crispness). Correlations between sensory and instrumental texture measures were high in some instances (e.g. Spearman’s rank correlations for Digi-Test M1 and sensory firmness at the University of Minnesota were 0.73 and 0.75 in 2010 and 2011, respectively). Phenotypic data for the RosBREED apple reference germplasm set, including many components of texture, flavor, appearance and storage disorders, are curated and available for use by the international community of apple breeders and allied scientists in the Breeders Toolbox at the Genome Database for Rosaceae (www.rosaceae.org).