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A. Nepal and L. del Río North Dakota State University

Characterizing moisture requirements for carpogenic germination of Sclerotinia sclerotiorum. 3 rd Annual Meeting of Midwest Weather Working Group Charlotte, NC August 2010. A. Nepal and L. del Río North Dakota State University. Disease triangle. Environment. Pathogen. Host. A. Lamey.

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A. Nepal and L. del Río North Dakota State University

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  1. Characterizing moisture requirements for carpogenic germination of Sclerotinia sclerotiorum 3rd Annual Meeting of Midwest Weather Working Group Charlotte, NC August 2010 A. Nepal and L. del Río North Dakota State University

  2. Disease triangle Environment Pathogen Host

  3. A. Lamey Sclerotinia stem rot disease cycle (Sclerotinia sclerotiorum)

  4. Objectives • Characterize role of soil moisture on carpogenic germination of S. sclerotiorum sclerotia • Characterize the role of sclerotial moisture on carpogenic germination

  5. Methods soil moisture • Ten moisture levels: constant: 25-100% at 25 unit intervals fluctuating: from 100, 75, 50, and 25 to 0% at 25 unit intervals • Five soil mixtures • Twenty sclerotia from four S. sclerotiorum isolates • Incubation at 18/14 oC • Experiment with 3 reps, conducted twice

  6. Results Physical propertiesof five soil mixtures used X Organic matter content (%) Y Silty clay : Sand (v/v)

  7. 75% of saturation 100% field capacity

  8. Results

  9. Main effect of soil texture on carpogenic germination Results Sandy loam Sandy loam Loamy sand Sand Silty clay

  10. Effect of fluctuating soil moisture conditions on carpogenic germination Results Soil moisture (% saturation )

  11. Time to first apothecium production Results

  12. Methods sclerotial moisture Water imbibition by sclerotia in soil • Three sclerotial sizes (L, M, and S) • Three soil textures: Silty clay (1:0), sandy loam (2:1), and sandy (0:1) • Four constant soil moisture levels: 100 - 25% saturation at 25 unit intervals • Sclerotial imbibition estimated hourly Effect of sclerotial imbibition on CG • Four sclerotial hydration levels: 100%, 70-80%, 40-50%, and 20-30% • Incubation at 18/14 oC • Experiment with 3 reps, conducted twice • Sclerotia incubated up to 90 days

  13. Results Dynamics of water absorption by sclerotia as a function of soil moisture

  14. Results Effect of sclerotial hydration on carpogenic germination of S. sclerotiorum Level of sclerotial hydration (%)

  15. Conclusions • CG significantly affected by soil texture, soil moisture, and their interaction • Fluctuations in soil moisture reduce CG • Best CG occurred at constant 25% saturation or 75-50% fluctuation, while constant 100% was detrimental • Sandy loams had highest CG, silty clay had lowest

  16. Conclusions • Sclerotia can become fully imbibed with water even if soil remains at 25% water saturation • CG is drastically reduced if sclerotia are not fully imbibed in water • Model development?? • Role of soil temperature??

  17. Acknowledgements • USDA-ARS/Sclerotinia Initiative • North Dakota Canola Growers Association

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