Exploring novel seed-treatment options to mitigate the impact of blackleg on canola
Date: February 2023
Term: 3 years, ending February 2023
Status: Completed
Researcher(s): Gary Peng, AAFC; Dilantha Fernando, University of Manitoba; Ralph Lange, InnoTech Alberta
SaskCanola Investment: $247,500
Total Project Cost: $247,500
Funding Partners: n/a
Grower Benefits
Lm inoculum at >105 spores/g soil can result in severe blackleg via root infection, especially if roots are wounded (by root maggots, for example).
Fluopyram, Saltro and Bion seed treatments look promising against the early blackleg infection; the rate may be finetuned for extended protection and more consistent efficacy.
None of these seed treatments has shown significant efficacy on any of the resistant canola cultivars tested under field conditions.
The study showed the potential of several new products for seed treatment against blackleg infection from cotyledon/leaf wounds, but the efficacy has mostly been observed on susceptible canola cultivar only. The product rate may be finetuned for extended protection of leaves and more consistent efficacy under field conditions. Some further research is warranted.
Project Summary
In addition to via wounds on cotyledons and lower leaves, the study found that early blackleg infection can occur also via roots. Seed treatment with several new products, including Fluopyram, Saltro and Bion, may help lower the risk of infection via both foliar and root pathways on a susceptible canola cultivar only, but results from field trials are still too variable. The rate of treatment may be finetuned to improve the efficacy and consistency. None of the treatments showed significant efficacy on resistant canola cultivars under field conditions, in which the disease level was generally low already.
Despite the widespread use of resistant canola cultivars, blackleg continues to occur in western Canada, with variable severity depending on the region and year. Increasing evidence shows that early infection is important, which can be through cotyledon, lower leaves and even roots. This early infection may be targeted by seed treatment, but the concurrent products, either Helix® or Prosper®, are ineffective to the infection pathways. Therefore, this study was aimed to: 1) understand the soil inoculum level of, blackleg pathogen required to cause root infection which would lead to severe blackleg, 2) evaluate new commercial products for potential seed treatment against the early blackleg infection, 3) assess the rate effect of top candidates for maximum efficacy, and 4) validate the efficacy in multi-site/year field trials.
Under greenhouse conditions, blackleg pathogen inoculum was applied as a soil drench at 0-108 spores/g soil to cause infection via roots. Roots of certain plants were wounded by cutting to simulate soil insect damage. About a dozen of new seed-treatment candidates were evaluated for restricting infection on cotyledons, and promising candidates were assessed further for control of root infection. Top candidates were also tested in field trials by targeted inoculation either on different leaves or via roots (soil drench inolation).
The drought of 2021 and early dry conditions in Saskatoon of 2022 affect the infection development after inoculation; many inoculated leaves had dropped before the pathogen was able to spread into the stem, so the disease levels were much lower than other years, despite the inoculation applied.
The study shows that: 1) Lm inoculum at 104 to 105 pycnidiospores/g soil can cause root infection which ultimately results in severe blackleg, 2) the current seed treatments with Helix® or Prosper® are ineffective against the infection from either lower leaves or roots, but the new products Fluopyram, Saltro and BION appear promising against early blackleg infection, 3) The Fluopyram treatment at 75 g/100Kg seed (registered rate) showed stability in efficacy with delayed emergence under controlled environment, but failed to control blackleg significantly in field trials (P >0.05). Increasing the product rate to 300 g achieved significant efficacy against root infection. 4) The BION seed treatment reduced the blackleg severity via the cotyledon but not 1st-leaf inoculation on susceptible cultivar only, 5) The efficacy of seed treatment may be improved by increasing the rate of treatment, which warrants further investigation. 6) None of the seed treatments evaluated showed efficacy against blackleg on resistant canola cultivars. However, due to the relatively low cost, a seed treatment may still be a good insurance policy in case of resistance erosion.
Figure 1. Effect of root wounding at six days after plant emergence and soil inoculum concentration (# spores/g soil) on blackleg infection via canola roots in greenhouse trials. Note that plants at >105/g soil inoculum levels showed severe disease at the early flower stage, and many of them died shortly after that.
Figure 2. Infection severity on cotyledons of susceptible (Westar) and resistant (InVigor L157H) canola cultivars received seed treatment with different fungicides at 14 days post inoculation. Jockey has been registered in Australia for seed treatment against blackleg for years.
Figure 3. Effect of Bion seed treatment on disease incidence and disease severity index of blackleg originating from cotyledon inoculation on Westar (susceptible) and InVigor (resistant) in two 2021 field trials near Saskatoon, SK and Brandon, MB, respectively. Treatment means with the same letter and case do not differ (LSD, P >0.05).