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Field winterhardiness is a critical trait in rose cultivars (Rosa ×hybrida) grown in northern climates. Although the molecular basis of cold hardiness has been well documented in model organisms such as Arabidopsis thaliana, little is known about the genetics and mechanisms underlying winterhardiness in roses. This research aims to explore the genetic control of winterhardiness for application in breeding programs using quantitative trail loci (QTL) analysis in two biparental rose populations derived from cold-hardy roses of the Canadian Explorer Series Collection. Field winterhardiness was assessed as a complex trait with winter damage and regrowth recorded in multiyear and multilocation trials in Ontario and Saskatchewan, Canada. In addition, this research explored the relationship between field measurements and electrolyte leakage recorded under artificial conditions. Electrolyte leakage had limited utility for application in rose breeding programs as a substitute for field evaluation, but did enable identification of QTL associated with potential cold hardiness candidate genes. A QTL for electrolyte leakage mapped to a genomic region that harbors a CBF1-like transcription factor. A total of 14 QTLs associated with field winter damage and regrowth were discovered, and they explained between 11% and 37% of the observed phenotypic variance. Two QTL associated with winter damage and regrowth overlapped with a known QTL for black spot (Diplocarpon rosae) disease resistance, Rdr1, in an environment under high disease pressure. Due to the complexity of field winterhardiness and its direct reliance on intertwined factors, such as overall plant health, moisture status, snow cover, and period of prolonged sub-zero temperatures, field trials are the ultimate measurement of field winterhardiness. Transgressive segregation was observed for all traits, and it was most likely due to complementary gene action. Field winter damage and regrowth were highly heritable in single environments, but they were subject to genotype × environment interaction resulting from pest pressure and severe climatic conditions.

Growers of high-end ‘Pinot noir’ wine grapes (Vitis vinifera L.) commonly reduce yield by cluster thinning with the goal of increasing fruit quality; however, there are no objectively defined yield targets to achieve optimum fruit composition. Canopy leaf area relative to fruit yield can affect total soluble solids (TSS), and recommendations have been established for warm wine grape production regions. However, the relationship between leaf area and photoassimilation differs among climates and training systems. Leaf area to yield (LA:Y) ratios developed in warm, arid regions may not be suitable for cool, wet regions such as western Oregon. A 3-year field study was conducted to elucidate relationships between canopy to yield ratios and berry composition for ‘Pinot noir’. Vegetative growth and fruit yield were manipulated through competitive cover cropping and cluster thinning. Growth was manipulated in three ways: perennial red fescue (Festuca rubra L.) was grown in 1) both (Grass), 2) one (Alternate), or 3) neither (Tilled) of the alleyways flanking the vine row. Within each vineyard floor treatment, fruit clusters were thinned to one per shoot (Half Crop) or vines were left unthinned (Full Crop). Floor management influenced both canopy size and yield because of altered vine nitrogen (N) status. Effects of crop load on berry components were not always consistent between the crop load metrics used [yield to pruning weight (Y:PW) ratio or LA:Y]. In 2 years, TSS reached a maximum at similar LA:Y; however, this did not necessarily produce optimum TSS. Yield had the greatest influence on pH and total anthocyanins (ACY) in the highest yielding, coolest year. Crop load metrics were not reliable predictors of TSS because of the dominant effect of seasonal variation. Relationships between canopy to yield metrics and other berry components were partially explained by tissue N, photosynthetic photon flux (PPF) through the cluster zone, and/or yield. Cluster thinning to adjust yields may not alter source to sink relationships or canopy to yield ratios enough to overcome ripening limitations in cool climates. Only one wine vintage had sensory differences with Alternate-Half Crop and Alternate-Full Crop wines ranked high quality and Tilled-Half Crop and Tilled-Full Crop wines ranked low quality by both consumer and winemaker panels. Therefore, cluster thinning may have limited impact on wine sensory properties.