Monitoring Airborne Inoculum of Sclerotinia sclerotiorum at Canola Flowering and Relationships to Weather Conditions and Disease Incidence and Severity

• Author / Creator

  McBain, Eleanor

• Sclerotinia stem rot, caused by Sclerotinia sclerotiorum, is an important disease of canola (Brassica napus). Disease development is highly dependent on weather conditions and is initiated by infection of the petals by airborne ascospores, followed by mycelial progression into leaf and stem tissues. Improved stem rot forecasts would facilitate improved fungicide application decisions, reducing costs and enhancing disease control. Various methods to monitor airborne inoculum of S. sclerotiorum were compared and related to stem rot incidence and severity. These included a passive spore trap (Spornado) and petal test kits from private seed testing laboratories, as well as a GRIPST-2009 rotation impact sampler (rotorod). Canola petal samples were also tested for S. sclerotiorum infection by the Plant Health Lab, Alberta Agriculture, Forestry and Rural Economic Development. Petal infestation levels (coupled with weather variables) provided the strongest linear relationship to disease incidence (R2 = 86%) and severity (R2 = 87%) during early-mid flowering, when fungicide application decisions are made. However, the strength of the relationship varied during the flowering period. The airborne spore traps did not show as strong of a relationship to stem rot levels as the petal tests, with the Spornado accounting for 48% and 40% of the variation in disease incidence and severity, respectively, and the rotorod accounting for 52% and 50% of the variation. Significance testing of petal, Spornado and rotorod samples taken from five different locations within a field did not show different population means, suggesting that one sample per field may be sufficient for monitoring purposes; however, more testing is required, especially across fields of different sizes. Quantification of S. sclerotiorum DNA on petal and rotorod samples by quantitative PCR indicated that 1.0 × 10-4 ng DNA per canola petal or per cubic meter of air per hour during early flowering would result in a disease incidence >15%, the level at which fungicide application is generally recommended. Given the wide range of variables affecting Sclerotinia stem rot development, an integrated disease forecasting approach, which includes monitoring of ambient weather conditions and an inoculum detection method, should be employed to determine the optimal timing of fungicide applications.

• Subjects / Keywords

  • Sclerotinia sclerotiorum
  • Canola
  • Management
  • Control strategies
  • Forecasting
  • Spornado
  • Stem rot of canola

• Graduation date

  Fall 2022

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-qwme-3584

• License

  This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.