Investigating the conditions favoring Verticillium stripe development and yield losses in canola
Term: 3 years, beginning 2024
Status: Ongoing
Researcher(s): Sheau-Fang Hwang, U of A; Fouad Daayf, U of M
SaskCanola Investment: $174,466.67
Total Project Cost: $823,400
Funding Partners: WGRF, ACPC, MCGA
Objective
1. Examine the effects of interactions between V. longisporum and L. maculans in canola, combined with in-vitro studies and in-soil studies; established the relationship between yield and disease severity, and the effect of inoculum timing on disease development under field conditions.
2. Evaluate the effect of soil pH on growth of V. longisporum and disease development and severity.
3. Screen canola lines and accessions for resistance to V. longisporum and use genome-wide association mapping to identify single nucleotide polymorphism (SNP) markers for resistance to this pathogen.
4. Investigate the impact of canola defenses on pathogen responses and adaptive mechanisms by: (i) Investigate how canola defenses to each pathogen affect the other pathogen, and how the latter reacts; (ii) Attempt to explain how potential pathogen adaptation mechanisms lead to the host-pathogen outcomes observed in the field.
5. Determine the pathogenicity and lineage of the collected V. longisporum isolates and the host specificity/range of this pathogen.
6. Assess the effects of VL seed infection rate on disease severity and direct examination of the impact of seed-to-seedling transmission.
Project Description
Verticillium longisporum survives as microsclerotia on crop residues and in the soil for up to 20 years, but also has been reported on plants in previously uninfested areas. As a monocyclic vascular pathogen, it may also be capable of invading seeds. V. longisporum was recovered from seeds in up to 13% of greenhouse-grown inoculated plants. Seed infection may impact seedling establishment, but even very low levels of seed transmission may be important when there is the potential to introduce the pathogen into a new area.
Under field conditions, the symptoms of blackleg and Verticillium stripe are superficially similar, resulting in potential misdiagnoses. Both result in discolouration of the stem interior, some disintegration of the exterior of the stem and the appearance of black fungal structures on the stem. Blackleg symptoms include stem cankering, while Verticillium often discolours half of the stem or leaf and later results in shredding of the outer layer of the stem. Blackleg produces pinhead-sized black pycnidia, while Verticillium produces pinpoint-sized black microsclerotia. Yield losses from both are caused by constriction of vascular tissue, cutting the flow of nutrients and water from the root to the upper plant. In addition, Verticillium often causes the stem to collapse, resulting in difficulties in harvesting. Moreover, there is evidence that these two pathogens often occur together and may act synergistically in canola according to preliminary work by Wang. Studying plant-pathogen interactions is important to understanding the dynamics of disease development and further develop effective disease control strategies. The nature and extent of plant-pathogen interactions can have a significant impact on crop productivity and quality.
Both L. maculans and V. longisporum can cause significant losses in yield and crop quality. L. maculans infects canola mainly at the seedling and early vegetative stages, whereas V. longisporum manifests later. In spite of differences in infection timing/mechanisms, these pathogens have similarities in their life cycles and may co-exist in canola fields, leading to potentially additive or synergistic disease effects.
Understanding the nature of L. maculans-V. longisporum interactions in canola cropping is critical for developing sustainable integrated disease management strategies, but very few studies have explored this issue. The recent identification of both diseases together in canola fields in Manitoba evokes even more complexity because it involves interactions, not only between the two pathogens, but also with the crop and the environment in which they interact (soil, soil microbiome, environmental conditions, rotational crops, etc.).
Preliminary results indicate that Verticillium stripe is more severe in neutral to basic soils than in acidic soils and that disease development is favoured by neutral-basic medium. Additional research is needed to confirm these data and establish the effects of pH on disease development. Moreover, little is known regarding the extent of yield losses and their relationship to Verticillium severity in Canada.
A previous study found that different oilseed rape cultivars had different quantities of V. longisporum DNA in the pods and seeds, supporting previous reports of quantitative resistance in the shoots, and indicating that breeding for host resistance may reduce the risk of seed transmission of this pathogen.
Direct interactions between the two pathogens can be studied under controlled conditions (antagonism, synergy, competition, etc.). This can provide insights into the dynamics of this interaction and potential competitive advantages between L. maculans and V. longisporum. However, the actual intricacies of the interactions between these two pathogens can only be fully understood by considering the host plant(s), prospective hosts in the cropping location, and the environment (i.e., soil, microbiome). As in other crops, interactions between canola and each pathogen affects susceptibility/resistance to other pathogens due to the complex interactions between plant defense mechanisms and the ability of pathogens to overcome such defenses. Examining the spatiotemporal interactions under experimental settings that mimic the natural conditions will shed light on how each pathogen (L. maculans and V. longisporum) affects the disease outcome and modulates further influences crop yield and quality. Doing so will ensure the development of sound disease resistance strategies.