Winter canola generally produces greater yields than spring canola. However, its range is limited due to its inability to withstand the harsh winter conditions that occur in many northern regions of the U.S.A. To identify loci associated with freezing tolerance in canola, we conducted a genome-wide association study (GWAS) using a genotyped diversity panel containing 399 accessions consisting primarily of winter canola. One-month-old greenhouse grown plants were subsequently cold-acclimated for two months in an environmental growth chamber prior to phenotyping for freezing survival using a visual damage scale and chlorophyll fluorescence (Fv/Fo). There was reasonable correlation observed between visual damage and chlorophyll fluorescence ratings among the top associated loci; the results indicated that some loci contributed to both freezing damage/tolerance and photosynthetic efficiency. The resulting numerical values for phenotypes were used for association analyses with the identified SNPs. Thirteen significant markers were identified on nine chromosomes for the phenotypes scored, with several showing significance for multiple phenotypes. Twenty-five candidate genes were identified as previously associated with freezing tolerance, photosynthesis, or cold-responsive in canola or Arabidopsis.

Forage crop–dairy farming is an important agro-industry across the world. This system is intensive with high-input forage crops. In the United States (US) Southern Great Plains, the system is based primarily on high-input annual grass-type crops in monocropping approaches and requires diverse low-input broadleaf crops for strengthening its sustainability. Winter canola (Brassica napus L.) and pea (Pisum sativum L.) have the potential to provide forage crop diversity options with high forage yields of high quality. Winter canola and pea in mono- and mixed-cropping approaches at seeding ratios of canola/pea at 0:100, 25:75, 50:50, 75:25, and 100:0 were studied for yield and quality in 2015 and 2016 in Clovis, New Mexico (NM). Averaged over years, canola–pea at 75:25 and 50:50 seeding ratios produced similar biomass forage yield but higher than mono-pea by 43% and canola–pea at 25:75 and mono-canola cropping by 8%. The land equivalent ratio of all mixed-cropping treatments exceeded 1.0, with canola–pea at the 50:50 seeding ratio recording a land equivalent ratio of 1.15, indicating that mixed-cropping systems are better users of land resources. Total digestible nutrients and relative feed value were higher in canola–pea mixed cropping than in mono-canola and mono-pea cropping. Canola–pea mixed cropping achieved high yields (13.3 to 14.7 Mg·ha⁻¹) with improved forage quality, as well as improved crop and land productivity, with the potential to improve mechanical harvestability of vining pea, and strengthen the diversity and sustainability of forage crop–dairy farming in the Southern Great Plains under limited irrigation input of ~300 mm.

A diverse population (429 member) of canola (Brassica napus L.) consisting primarily of winter biotypes was assembled and used in genome-wide association studies. Genotype by sequencing analysis of the population identified and mapped 290,972 high-quality markers ranging from 18.5 to 82.4% missing markers per line and an average of 36.8%. After interpolation, 251,575 high-quality markers remained. After filtering for markers with low minor allele counts (count > 5), we were left with 190,375 markers. The average distance between these markers is 4463 bases with a median of 69 and a range from 1 to 281,248 bases. The heterozygosity among the imputed population ranges from 0.9 to 11.0% with an average of 5.4%. The filtered and imputed dataset was used to determine population structure and kinship, which indicated that the population had minimal structure with the best K value of 2–3. These results also indicated that the majority of the population has substantial sequence from a single population with sub-clusters of, and admixtures with, a very small number of other populations. Analysis of chromosomal linkage disequilibrium decay ranged from ~7 Kb for chromosome A01 to ~68 Kb for chromosome C01. Local linkage decay rates determined for all 500 kb windows with a 10kb sliding step indicated a wide range of linkage disequilibrium decay rates, indicating numerous crossover hotspots within this population, and provide a resource for determining the likely limits of linkage disequilibrium from any given marker in which to identify candidate genes. This population and the resources provided here should serve as helpful tools for investigating genetics in winter canola.