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Latent Infection of Soybean rust

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Latent Infection of Soybean rust

  1. 1. Documentation of an Extended Latent Infection Period with Phakopsora pachyrhizi in SoybeanN.A. Ward, R.W. Schneider LSU AgCenter
  2. 2. •Phakopsora pachyrhizi•Still a major disease ofsoybean in the southeasternUS•Preventative fungicideapplications result in largegrower inputs•Effective timing of fungicidesis the most effective means ofcontrol and/or prevention ofthe disease
  3. 3. Overwinters on kudzuSporulating pustules are oftendetected in January and FebruarySoybean symptoms at seed set (R5)
  4. 4. HypothesisLatent infection period can be longer than 10 days, regardless of weather conditions or inoculum load In laboratory and greenhouse, pustule development 7-10 days after inoculation Even under cool temperatures and humid conditions, disease symptoms do not occur in the field until mid-reproductive stages
  5. 5. ApproachUse qPCR to quantifyPhakopsora pachyrhiziHigh specificityDetects as little as 1 picogramof DNA of P. pachyrhiziin 10ng total DNA
  6. 6. Experimental 2009 – Baton Rouge, 3 soybean fieldsProcedure (April, May, and July) 2010 – New Iberia, kudzu (April) 2010 – Quincy, FL kudzu (March to October)
  7. 7. 2009
  8. 8. 2009 Parish Date Growth Stage St. Martin June 5 R4 Iberia June 24 R5 Acadia June 16 R5 Assumption July 27 R7 Near Baton Rouge Patricia Bollich, IPM Pipe
  9. 9. 2009 April SoybeansApr 17 June 4Planting R1 <43 days 60+ days qPCR negative qPCR positive Symptoms
  10. 10. 2009 May SoybeansMay 20 Jul 23 Sept 4Planting R1/R2 R6 64 days 43 days qPCR negative qPCR positive Symptoms
  11. 11. 2009 July SoybeansJuly 21 Aug 20 Sept 25Planting V4 R5 30 days 33 days qPCR negative qPCR positive Symptoms
  12. 12. 2009 SummaryApr 29 June 4Planting R1 60+ days May 20 Jul 23 Sept 4 Planting R1/R2 R6 43 days July 21 Aug 20 Sept 25 Planting V4 R5 33 days Aug 20 Green Stem
  13. 13. 2010
  14. 14. 2010 Weather
  15. 15. Compare to 2009
  16. 16. Sample Date +/-Stem April 3 - 2010 Results New Iberia Kudzu April 11 - Collection by Tomas Rush April 18 - April 27 -Leaf April 3 - April 11 - April 18 - April 27 - May 11 -
  17. 17. Latent Month County Symptoms Infection 2010 Gadsden KudzuMay Holmes - - North Florida Research Jackson and Education Center University of Florida Gadsden Quincy, FLJune - - Jackson Collection by Kelly O’BrianJuly Gadsden - - HolmesAugust - - Jackson GadsdenOctober Holmes -/+ -/+ Jackson
  18. 18. 2010 July Soybeans July 4 Aug 25 Sept 12Planting R3? R6? 52 days 18 days 43 days July 13 SBR Reported on nearby kudzu
  19. 19. 2009 Fungicide Time of Infection StudyR.W. Schneider, C. L. Robertson
  20. 20. Field Views of FungicideTreatments Nonsprayed Topguard, 7 0z, control R1
  21. 21. Summary:2009 – early sources of inoculum early infection2010 – late or no inoculum late or no infectionInfection detected V4 to R2/R3Disease symptoms R4 to R6
  22. 22. Conclusion:Latency is afunction of plantgrowth stage.Infection can takeplace long beforediseasesymptoms occur.Fungicides shouldbe applied atonset of latentinfection.
  23. 23. Acknowledgements

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