Location: Sunflower Research
2012 Annual Report
Ascospores are produced in vitro and collected for field use. By comparing the infection levels of these two infection mediums in the field under five defined misting and several soil water regimes we will determine which parameters are necessary to effectively establish a Sclerotinia stalk rot epidemic in canola. The environmental conditions will be recorded with a North Dakota Agricultural Weather Network station located at the Langdon Research Extension Center and microclimates will be carefully monitored with Onset leaf wetness sensors placed at three levels within the canopy, soil water measurements and disease assessments. Disease incidence will be quantified by collecting petals and plating on selective media for Sclerotinia sclerotiorum. The petals will be sampled from multiple levels within the canopy during the flowering growth period. The most effective concentration of ascospores for infection will be determined by applying several ascospore concentrations to the canola at different timings with and without supplemental water application that modify the microclimates over the growing season. In addition, the benefit of cultivars with different flowering windows will be compared at multiple planting dates in these environments with buried sclerotia and backpack applied ascospores.
This project has two components, determining factors influencing apothecia formation (carpogenic germination of sclerotia) and the role that the source of inoculum, inoculum concentration and timing of inoculation, as well as moisture play on disease development; both involve field and controlled environment experiments. To date, we evaluated the effect of water imbibition by sclerotia on carpogenic germination by using temperatures that fluctuated between 14 and 18°C; these temperatures represent day and night mean temperatures during the flowering stage of canola in North Dakota. Results of these studies indicated that sclerotia can reach full hydration even if the soil is kept at 25% of its water saturation capacity; further, the highest carpogenic germination was observed on sclerotia that were fully hydrated. Reduced levels of carpogenic germination were observed on sclerotia that were allowed to hydrated to -80% of its capacity, but no germination was observed when sclerotia were kept at 50% of its hydration capacity. Studies to characterize the effect of water temperature on the ability of sclerotia to hydrate were conducted in the winter of 2010-11. While colder temperatures reduced the rate of water absorption, they did not keep sclerotia from reaching full hydration. A manuscript titled "Effect of sclerotial water content on carpogenic germination of Sclerotinia sclerotiorum" was completed and is currently “in press” in Plant Disease. A laboratory study comparing the effect of three different conditioning methods on carpogenic germination of sclerotiacontinues and preliminary results indicate that alternating eight 24 hour cycles of freeze and thaw induces germination of sclerotia better than four cycles.