Blackleg disease is caused by the stubble-borne pathogen Leptosphaeria maculans and results in significant yield losses in canola (Brassica napus) worldwide. Control of this disease includes breeding for resistance, fungicides and cultural practices including stubble management. In recent years, cropping systems have changed with the introduction of no-till farming and inter-row sowing, and it is unknown what impact these changes have had on stubble retention. The aim of this study is to investigate the impact of inter-row sowing on stubble retention and spore release. The use of inter-row sowing resulted in 25–48% of stubble remaining standing (vertical) in fields after 1 year. Furthermore, spore release was significantly (P < 0.05) delayed in stubble that remained vertical in the field compared with stubble lying down, with total spore release from vertical stubble 66% less than from horizontal stubble. The impact these changes have on the epidemiology of blackleg disease remains unknown.

Light leaf spot, caused by Pyrenopeziza brassicae, is the most damaging disease problem in oilseed rape (Brassica napus) in the United Kingdom. According to recent survey data, the severity of epidemics has increased progressively across the UK, with yield losses of up to £160M per annum in England and more severe epidemics in Scotland. Light leaf spot is a polycyclic disease, with primary inoculum consisting of airborne ascospores produced on diseased debris from the previous cropping season. Splash-dispersed conidia produced on diseased leaves are the main component of the secondary inoculum. Pyrenopeziza brassicae is also able to infect and cause considerable yield losses on vegetable brassicas, especially Brussels sprouts. There may be spread of light leaf spot among different Brassica species. Since they have a wide host range and frequent occurrence of sexual reproduction, P. brassicae populations are likely to have considerable genetic diversity, and evidence suggests population variations between different geographic regions, which need further study. Available disease-management tools are not sufficient to provide adequate control of the disease. There is a need to identify new sources of resistance, which can be integrated with fungicide applications to achieve sustainable management of light leaf spot. Several major resistance genes and quantitative trait loci have been identified in previous studies, but rapid improvements in the understanding of molecular mechanisms underpinning B. napus–P. brassicae interactions can be expected through exploitation of novel genetic and genomic information for brassicas and extracellular fungal pathogens.

Cultivation of canola (oilseed rape, rapeseed; Brassica napus) in many parts of the world relies on the use of cultivars carrying resistance genes that recognise avirulence products of the major canola pathogen, Leptosphaeria maculans. However, widespread cultivation of plants with such resistance provides the potential for evolution of the pathogen population to overcome resistance by altering the proportion of avirulence v. virulence alleles. In this study, the frequencies of avirulence genes were measured for 2091 Australian isolates dating from the late 1980s to present. Frequencies of avirulence genes changed over time. Analysis of isolates from the Eyre Peninsula, where canola is intensively cultivated, indicated that changes in allele frequencies at the AvrLm1, AvrLm4 and AvrLm6 loci could be correlated with the widespread planting of cultivars carrying specific resistance genes. These data show that determining avirulence allele frequencies in L. maculans populations provides power to anticipate which cultivars will be most successful in future growing seasons.

As climatic changes occur over the coming decades, our scientific understanding of plant responses to environmental cues will become an increasingly important consideration in the breeding of agricultural crops. This review provides a summary of the literature regarding vernalization research in Brassicaceae, covering both the historical origins of vernalization research and current understanding of the molecular mechanisms behind the regulatory pathways involved in vernalization and subsequent inflorescence. We discuss the evolutionarily conserved biology between the model organism Arabidopsis thaliana and the Brassica genus of crop cultivars and contrast the differences between the genera to illustrate the importance of Brassica-specific research into vernalization.

Blackleg disease, caused by the ascomycete fungal pathogen Leptosphaeria maculans, is a devastating disease of canola (Brassica napus) in Australia, Canada and Europe. Although cultural strategies such as crop rotation, fungicide application, and tillage are adopted to control the disease, the most promising disease control strategy is the utilisation of resistant canola varieties. However, field populations of L. maculans display a high evolutionary potential and are able to overcome major resistance genes within a few years, making disease control relying on resistant varieties challenging. In the early 1990s, blackleg resistance gene Rlm3 was introduced into Canadian canola varieties and provided good resistance against the fungal populations until the early 2000s, when moderate to severe blackleg outbreaks were observed in some areas across western Canada. However, the breakdown of Rlm3 resistance was not reported until recently, based on studies on R genes present in Canadian canola varieties and the avirulence allele frequency in L. maculans populations in western Canada. The fact that Rlm3 was overcome by the evolution of fungal populations demands canola breeding programs in Canada to be prepared to develop canola varieties with diversified and efficient R genes. In addition, frequent monitoring of fungal populations can provide up-to-date guidance for proper resistance genes deployment. This literature review provides insights into the outbreaks and management of blackleg disease in Canada.

The selection of cultivars with high carotenoid content represents a novel goal in the genetic improvement of oilseed rape. The successful development of an efficient method for the quantification of carotenoids in oilseed rape is a prerequisite for this breeding initiative. In the present study, ultrasound-assisted extraction was combined with a spectrophotometric method to quantify seed carotenoid levels in oilseed rape. The key variables were optimised as follows: the solvent used was a 1 : 1 (v : v) mixture of petroleum ether and acetone, the solid to solvent concentration was 0.08 g/mL, the ultrasound frequency and power were set at 45/100 (kHZ/w), and three extractions of 15 min each were performed. Compared with the conventional solvent extraction method, the time required for extraction using the ultrasound-assisted extraction method was significantly shortened (by 24 times), and the reproducibility was also remarkably improved. These results indicate that ultrasound-assisted spectrophotometric quantification is a rapid, accurate, simple and low cost tool for the screening and selection of rapeseed cultivars with high carotenoid content.

Brassica napus (rapeseed, canola) is an important oilseed crop worldwide as well as a recent agricultural hybrid species, resulting from crosses between progenitor B. rapa (turnip) and B. oleracea (cabbage) species in the last few thousand years. No wild form of B. napus is known to exist, making B. napus an interesting model for studies of genetic and genomic evolution in a polyploid under agricultural selective pressure. We generated genotype (Illumina Infinium 60K Brassica array) and phenotype data for elite spring-type B. napus lines from Australia, China and India (only one line). Phenotypically, plant growth, silique development and flowering traits were more likely to differentiate Chinese germplasm, whereas resistance to blackleg disease, secondary branching and seed traits were more likely to differentiate Australian germplasm. Genetic differentiation between the Australian and Chinese populations was low (F_ST = 0.035). Genetic relationship was not a predictor of similarity in yield traits between lines. Presence–absence variants were detected across the population: variants shared by at least three lines were present in every chromosome in the B. napus genome, and large missing chromosome segments (>1 Mbp) putatively due to A–C genome translocations were observed on chromosomes A7, A10, C1, C2, C6, C8 and C9. Our results highlight that widespread presence–absence variation is usual in B. napus, and may suggest that phenotypic and genetic diversity are not closely linked within spring-type B. napus from Australia and China, although the low sample numbers in our study prevent strong conclusions. We propose that inbreeding and low levels of genetic diversity, coupled with exchanges between the A and C genomes, were major driving forces behind genome evolution in this recent agricultural crop species.

Blackleg, caused by Leptosphaeria maculans, is the main disease constraint for canola production in Australia. The fungus infects all aboveground and belowground parts of the canola plant. Yield loss in Australia and worldwide is generally associated with cankers at the crown, which arise from leaf infections during the early stages of seedling growth. Infection of flowers, peduncles, siliques, main stems and branches, with resultant lesions and canker formation, are typically uncommon symptoms. We propose the term ‘upper canopy infection’ to encompass symptoms on all of these plant parts because they generally occur together on the same plant and appear after the plant has undergone elongation. Branch and stem lesions observed in a commercial crop in 2010 were confirmed as L. maculans. Since then, assessment of upper canopy symptoms at 25 sites across the canola-producing regions of Australia between 2011 and 2016 show that symptoms are more prevalent, although they differed between sites and seasons. In 2011, symptoms were present at a single site, and this increased to seven sites in 2013 and 23 sites in 2016. Preliminary data indicate that infection arises from both ascospore and pycnidiospore inoculum, and that earlier onset of flowering is a key risk factor for more severe upper canopy infection. Evidence suggests that host genetic resistance may be an effective control for upper canopy infection.

Plant disease-resistance genes play a critical role in providing resistance against pathogens. The largest family of resistance genes are the nucleotide-binding site (NBS) and leucine-rich repeat (LRR) genes. They are classified into two major subfamilies, toll/interleukin-1 receptor (TIR)-NBS-LRR (TNL) and coiled-coil (CC)-NBS-LRR (CNL) proteins. We have identified and characterised 641 NBS-LRR genes in Brassica napus, 249 in B. rapa and 443 in B. oleracea. A ratio of 1 : 2 of CNL : TNL genes was found in the three species. Domain structure analysis revealed that 57% of the NBS-LRR genes are typical resistance genes and contain all three domains (TIR/CC, NBS, LRR), whereas the remaining genes are partially deleted or truncated. Of the NBS-LRR genes, 59% were found to be physically clustered, and individual genes involved in clusters were more polymorphic than those not clustered. Of the NBS-LRR genes in B. napus, 50% were identified as duplicates, reflecting a high level of genomic duplication and rearrangement. Comparative analysis between B. napus and its progenitor species indicated that >60% of NBS-LRR genes are conserved in B. napus. This study provides a valuable resource for the identification and characterisation of candidate NBS-LRR genes.

Broadening of genetic diversity in spring oilseed Brassica napus L. (AACC, 2n = 38) canola is important for continued improvement of this crop. For this, the vast allelic diversity of the A genome of Brassica rapa L. (AA, 2n = 20) can be utilised. We investigated the prospect of developing canola-quality euploid B. napus lines carrying the alleles of B. rapa from F₂ and BC₁ (F₁ × B. napus) populations of three B. napus × B. rapa interspecific crosses involving one B. napus and three genetically distinct B. rapa parents. In meiosis, the F₁ AAC hybrid was expected to show normal segregation for the A genome chromosomes, whereas a range of C chromosomes from zero to nine was expected to be included in the gametes due to random segregation of this haploid set of chromosomes. Subsequent self-pollination, theoretically, should have eliminated the unpaired C chromosomes and resulted in a majority of B. rapa type. However, no B. rapa-type progeny were detected, and all progeny in the F₈ conformed to be B. napus type. Correlation between parent and offspring generation, grown in greenhouse or field, was weak to moderate for seed glucosinolate content; however, the simpler genetic control of this trait, involving only the A genome loci, allowed the development of low-glucosinolate lines from this interspecific cross. Of the theoretical number of simple sequence repeat (SSR) marker alleles of B. rapa expected to be present in F₄ and F₈ populations, about 45% were detected in these populations, suggesting that the loss of these marker alleles occurred prior to the F₄ generation. Loss of several SSR loci was also detected in these populations, which probably resulted from homoeologous pairing and rearrangements of the chromosomes of the A and C genomes. Genetic diversity analysis performed on the F₈ progeny of two crosses showed that the two populations clustered into distinct groups, which demonstrates that they inherited SSR B. rapa alleles unique to each B. rapa parent. We conclude that B. rapa alleles from diverse sources can be readily incorporated into B. napus progeny by this interspecific crossing method.

DNA methylation is an epigenetic gene regulatory mechanism that plays an essential role in gene expression, transposon silencing, genome imprinting and plant development. We investigated the influence of DNA methylation on gene expression in Brassica rapa L., to understand whether epigenetic differences exist between inbred lines. Genome-wide DNA methylation was analysed by methylated DNA immunoprecipitation sequencing (MeDIP-seq) of 14-day-old first and second leaves from two inbred lines of Chinese cabbage, one susceptible and one resistant to fusarium yellows caused by Fusarium oxysporum f. sp. conglutinans. MACS (model-based analysis for ChIP-seq) identified DNA methylation peaks in genic regions including 2 kb upstream, exon, intron and 2 kb downstream. More than 65% of genes showed similar patterns of DNA methylation in the genic regions in the two inbred lines. DNA methylation states of the two inbred lines were compared with their transcriptome. Genes having DNA methylation in the intron and in the 200 bp upstream and downstream regions were associated with a lower expression level in both lines. A small number of genes showed a negative correlation between differences in DNA methylation levels and differences in transcriptional levels in the two inbred lines, suggesting that DNA methylation in these genes results in transcriptional suppression.