Sclerotinia stem rot (SSR) is a fungal disease of rapeseed/canola that causes significant seed yield losses and reduces its oil content and quality. In the present study, the reaction of 187 diverse canola genotypes to SSR was characterized at full flowering stage using the agar plug to stem inoculation method in four environments. Genome-wide association study (GWAS) using three different algorithms identified 133 significant SNPs corresponding with 123 loci for disease traits like stem lesion length (LL), lesion width (LW), and plant mortality at 14 (PM_14D) and 21 (PM_21D) days. The explained phenotypic variation of these SNPs ranged from 3.6 to 12.1%. Nineteen significant SNPs were detected in two or more environments, disease traits with at least two GWAS algorithms. The strong correlations observed between LL and other three disease traits evaluated, suggest they could be used as proxies for SSR resistance phenotyping. Sixty-nine candidate genes associated with disease resistance mechanisms were identified. Genomic prediction (GP) analysis with all the four traits employing genome-wide markers resulted in 0.41–0.64 predictive ability depending on the model specifications. The highest predictive ability for PM_21D with three models was about 0.64. From our study, the identified resistant genotypes and stable significant SNP markers will serve as a valuable resource for future SSR resistance breeding. Our study also suggests that genomic selection holds promise for accelerating canola breeding progress by enabling breeders to select SSR resistance genotypes at the early stage by reducing the need to phenotype large numbers of genotypes.

Sugar beet (Beta vulgaris L.) and canola (Brassica napus L.) are major crops in North Dakota, with sugar beet production primarily in the eastern part of the state in the Red River Valley and canola production across the northern half of the state. Both crops are hosts of sugar beet cyst nematode (SBCN), Heterodera schachtii Schmidt. In April 2011, soil samples were collected from four sugar beet fields belonging to three growers who believed the fields were infested with SBCN. The fields were located in a 65-km2 area in the Yellowstone Valley of western North Dakota. Cysts were extracted by sieving and Heterodera-like cysts with eggs were observed in all four soil samples. Population densities in the four fields ranged from 100 to 1,750 eggs/100 cm3 soil. Sugar beet seedlings (cv. M832224) were grown in a potting mix for 6 weeks in the greenhouse and then transferred to conetainers (type D40; volume 656 ml) containing autoclaved river sand. Conetainers were placed in sand in plastic pots immersed in a water bath at 27°C. Three plants were each infested with 800 eggs from field No. 2. After 55 days of incubation, the average number of females was 115 per plant. A similar experiment was conducted with canola cvs. Hyclass 940, Caliber 30, and Westar, which were inoculated with 500 eggs each from field No. 2. After 53 days of incubation, there was an average of 39, 20, and 30 females for each respective cultivar. Flask-shaped cysts (n = 26) from canola roots were light to dark brown; the vulval cone was ambifinestrate with dark brown, molar-shaped bullae positioned underneath the vulval bridge. Body length (excluding neck) ranged from 600 to 850 μm (mean 701.2 μm); body width, 350 to 580 μm (mean 469.2 μm); and length/width ratio, 1.2 to 1.8 (mean 1.5). Second-stage juvenile (J2) (n = 21) body length ranged from 400 to 485 μm (mean 437.1 μm); stylet length was 25 μm (no variation) with forwardly directed knobs; conical tail with rounded tip ranged from 37.5 to 55.0 μm long (mean 46.6 μm) with hyaline region from 20.0 to 32.5 μm (mean 27.3 μm); and lateral field presented four incisures. These morphometrics were used to identify H. schachtii according to Subbotin et al. (4). Confirmation of identification was by amplification and sequencing of a 28S rDNA gene fragment (1) from individual females (GenBank Accession No. JQ040526), which was 100% identical to H. schachtii 28S rDNA sequence (GenBank Accession No. GU475088). To our knowledge, this is the first confirmed report of H. schachtii in North Dakota. A 1958 report of SBCN in North Dakota (2) was not subsequently confirmed (3). Because there is extensive canola production across the northern part of the state bordering western and eastern sugar beet- production areas, canola may serve as a bridge for movement of SBCN from west to east. SBCN is a potential threat to these two important crops. References: (1) A. Amiri et al. Eur. J. Plant Pathol. 108:497, 2002. (2) F. Caveness. J. Sugar Beet Res. 10:544, 1958. (3) P. Donald and R. Hosford. Plant Dis. 64:45, 1980. (4) S. A. Subbotin et al. Systematics of Cyst Nematodes (Nematoda: Heteroderinae). Nematology Monographs and Perspectives. Vol. 8B. Brill, The Netherlands. 2010.

Clubroot is a soil-borne disease caused by Plasmodiophora brassicae, that is emerging as a production problem in North Dakota (ND), which contributes approximately 90% of the total US canola production. P. brassicae’s resiliency in the soil and its ability to overcome the genetic resistance available in commercial hybrids make this a significant threat to canola production in the state and highlights the need to identify additional sources of resistance. To this effect, 115 Brassica napus plant introduction accessions were evaluated for their reaction to clubroot in field trials conducted between 2019 and 2021 in a naturally infested field. Seven accessions with high levels of clubroot resistance were identified. These resistant materials may contribute to widening the genetic resistance base of modern canola cultivars.