Fusarium root rot of canola (Brassica napus): Occurrence, pathogenicity and yield losses in Alberta, Canada
Creators: Yu, Haitian
Publisher: name: University of Alberta Library
Year: 2024

<p>Root rot is a soilborne disease of canola (Brassica napus) caused by a pathogen complex. Canola crops were surveyed in Alberta, Canada, in 2021 and 2022 to assess the composition and diversity of fungi associated with root rot in this region. Isolates were identified to genus and/or species based on colony and morphological characteristics, with Fusarium spp. found to be predominant. The identity of Fusarium spp. was confirmed by analysis of the translation elongation factor 1-α (TEF-1α) and internal transcribed spacer (ITS) sequences. Fusarium avenaceum was recovered most frequently, followed by F. redolens and F. solani. Most isolates caused moderate to severe disease on canola under greenhouse conditions, with F. avenaceum and F. sporotrichioides among the most aggressive species. Fusarium sporotrichioides and F. commune were identified for the first time as canola root rot pathogens. Principal component analysis demonstrated the utility of combining disease severity and growth measurements in assessments of pathogenicity. Analysis of the ITS sequence successfully distinguished various Fusarium species, with the exception of closely related phylogenetic species like F. avenaceum, F. acuminatum, and Fusarium tricinctum. The TEF-1α sequence analysis facilitated species differentiation. Concatenating the ITS and TEF-1α sequences provided more diversified grouping information. No geographic or year effects were observed on fungal diversity or aggressiveness. In another study, the impact of F. avenaceum and Fusarium proliferatum on canola yields was evaluated in field and greenhouse experiments, and the interaction between F. proliferatum and F. oxysporum was also explored. Inoculation with any of the three species resulted in significant disease severity and reduced seedling emergence compared with non-inoculated controls, leading to yield reductions of up to 35%. Notably, there was a strong correlation (r = 0.93) between root rot severity at the seedling stage and at maturity. Regression analysis indicated a linear decline in emergence with increasing disease severity. Furthermore, disease severity at maturity adversely affected pod number per plant and seed weight per plant, with both parameters ultimately reaching zero at a severity of four on a 0-4 scale. Co-inoculation with F. oxysporum and F. proliferatum induced more severe root rot than inoculation with each species on its own, suggesting synergistic interactions between these fungi. In a final study, the host range of F. proliferatum was investigated through greenhouse inoculation experiments involving wheat, barley, faba bean, pea, lentil, canola, lupine and soybean. All crops were at least partly susceptible, developing mild to severe root rot at the seedling and adult plant stages, and showing significant reductions in growth. In general, barley and wheat demonstrated higher tolerance to infection, followed by faba bean and pea. Soybean, canola, lupine, and lentil were most susceptible. Canola and soybean were particularly vulnerable to F. proliferatum at the pre-emergence stage, while infection greatly reduced lentil biomass. Reductions in barley emergence and other growth parameters, however, occurred only under a high inoculum concentration. Understanding the identity, pathogenicity, and relative prevalence of Fusarium spp., along with improved knowledge of their impact on yields, will contribute to better management of canola root rot.</p>