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The temporal patterns of Sclerotinia sclerotiorum ascospore dispersal in canola fields were studied at two North Dakota locations between 2005 and 2007. Seven-day volumetric spore samplers were used to monitor airborne ascospore populations while electronic data loggers recorded hourly information on air temperature, relative humidity, soil moisture and soil temperature under the canola canopy. Ascospore dispersal occurred during single periods that lasted 4 to 6 hours. In 2005 and 2007, most ascospores were collected between 10 am and 1 pm; however, in 2006, a drier than normal year, most were collected between 2 am and 7 am. In 2005 and 2007, the first sharp increase in ascospore dispersal was preceded by a 10-unit drop in relative humidity from close to saturation, and an increase in air temperature of 5 °C. In 2006, however, no significant changes in relative humidity, which remained around 90%, or air temperature, which hovered around 15 °C, were recorded prior to the start of the discharges. These nighttime discharges lasted 2 hours longer than daytime discharges. Daily discharges, daytime and nighttime, started when relative humidity was ≥ 90% and air temperature was around 15-16 °C. Multiple peak-days, days with mean ≥ 20 ascospores m-3, were recorded in 2005 and 2007, but none were recorded in 2006. Peak-days were associated with preceding periods of seven consecutive days with mean relative humidity ≥ 85% in the canola canopy. [ABSTRACT FROM AUTHOR]

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., (© 2021. The Author(s).)

Genetic and phenotypic diversity and population differentiation of Sclerotinia sclerotiorum isolates infecting canola from China and the United States were investigated. Genetic diversity was assessed with eight microsatellite markers and mycelial compatibility groups (MCGs). Phenotypic diversity was assessed with sensitivity to three fungicides, production of oxalate and sclerotia, growth rate, and virulence on two canola cultivars. No shared MCGs or multilocus haplotypes were detected between the two populations, and populations differed significantly (P < 0.001). Recombination was detected in both populations but was greater in the Chinese population. A polymerase chain reaction detection assay showed that ~60% of the isolates were inversion-plus at the mating type locus. The two populations differed significantly (P < 0.05) for all of the phenotypic traits except for sensitivity to fungicide fluazinam and virulence. Isolates in the Chinese population were unique in several aspects. Despite the phenotypic differentiation, heritabilities of the phenotypic traits were similar for both populations. Significant correlations were found among five phenotypic traits. Cross resistance to benomyl and iprodione was detected. Virulence was not significantly correlated with any other phenotypic trait and had the least heritability. However, both populations were equally virulent on either a susceptible or a moderately resistant canola cultivars.