Quantitative trait locus analysis of tolerance to temperature fluctuations in winter, fruit characteristics, flower color, and prickle-free canes in raspberry

Despite the interest in growing raspberries (Rubus idaeus) in the southeastern USA, production is limited by the lack of cultivars adapted to the climate. One of these major climate adaptations is the ability to tolerate fluctuating winter temperatures. Perennial plants have adapted to these conditions by having high chilling requirements. Breeding efforts are underway for developing adapted cultivars, but breeding improvements in Rubus is a time-consuming process. In order to expedite the breeding process, molecular breeding tools are being developed. In this work, the cross (Rubus parvifolius x Tulameen) x Qualicum was used for the construction of a genetic linkage map and for quantitative trait locus (QTL) analyses of chilling requirement, prickle density, fruit color, fruit shape, fruit size, and flower color. Chilling requirements were determined by measuring bud break in chilled cuttings; all other traits were scored visually. Seven linkage groups were constructed and compared to an established Rubus map. Four regions were associated with chilling requirement, and were mostly consistent across 3 years of evaluation. For the fruit and flower color traits, significant regions were consistent across 2 years, and either one or two QTL were found. Two QTL linked to prickle density were detected; one coincided with previous studies, while the second QTL was found in linkage group 4 and co-localized with the marker for lack of prickles. This region is proposed to contain gene s for the prickle-free trait.