Fruit texture phenotypes of the RosBREED U.S. apple reference germplasm set

Establishing marker-locus-trait associations to enable marker-assisted breeding depends on having an extensive, reliable database for phenotypic traits of interest in relevant germplasm. A reference germplasm set of 467 apple (Malus ×domestica Borkh.) cultivars, selections, and seedlings (referred to as individuals) was identified as part of the USDA-Specialty Crop Research Initiative (SCRI) project, RosBREED. The germplasm set provides efficient allelic representation of 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, focusing on fruit traits evaluated at harvest and after 10 and 20 weeks of refrigerated storage. Phenotypic data were collected for the sensory texture traits of firmness, crispness, and juiciness as well as for instrumental texture measures. In 2010 and 2011, fruit from 216 and 330 individuals, respectively, were harvested and a total of 369 individuals were evaluated over the two years. Correlations between sensory and instrumental texture measures were high in some instances. Moderate year-to-year repeatability of trait values was observed. Because each location had a largely unique set of individuals, as well as differing environmental conditions, means, ranges, and phenotypic variances differed greatly among locations for some traits. Loss of firmness and crispness during storage was more readily detected instrumentally than by the sensory evaluation.