Rp resistance Rp1-D-virulent isolates fungicides

1. Rp resistance • Rp1-D-virulent isolates • fungicides

2. Effect of rust on sweet corn yield EAR WEIGHT

3. Rp-resistance Bands of chlorotic flecks (no sporulation)

4. In the 1990s, Rp resistance added at least $3 million* annually to the value of processing sweet corn in the Midwest * based on four, relatively conservative assumptions

5. 250,000 A processing sweet corn Midwest 1. x 1/2 exposed to common rust 125,000 A exposed to rust 2. x 6.2 tons per A 775,000 tons 3. x $50 per ton $38,750,000 4. x 15% rust severity* x 0.5 % loss per 1% severity $2,906,250 loss * an average of 15% rust severity or more for hybrids rated MR to S

6. Probability* of severe rust Rust severity % and (estimated Reactions of sweet corn hybrids yield reductions)** R MR M MS S 0-10% (3%) 0.63 0.26 0.11 0.11 0.11 10-20% (9%) 0.37 0.47 0.16 0.11 0 20-30% (15%) 0 0.26 0.63 0.26 0.16 30-40% (21%) 0 0 0.11 0.32 0.26 40-50% (27%) 0 0 0 0.21 0.32 >50% (>30%) 0 0 0 0 0.16 * probability based on 19 trials in 18 years of evaluations in University of Illinois sweet corn hybrid disease nurseries - plants inoculated as seedlings ** yield loss estimated by multiplying rust severity by 0.6

7. Susceptible Rp-resistant

8. Rp1-D resistant hybrid Rock Falls, IL September 1999

9. Rp1-D resistance Los Mochis, Mexico March 2000

10. Questions about the Rp1-D-virulent race 1. How will hybrids react to the Rp1-D-virulent race? - non-Rp hybrids - Rp hybrids 2. Does Rp1-D have any “residual” effect on the new race?

11. Reactions of non-Rp hybrids

12. Reactions to Rp1-D-virulent and avirulent isolates 2001 UI hybrid disease nursery

13. Reactions to Rp1-D-virulent and avirulent isolates 2001 UI inbred disease nursery

14. Hybrids that do not have the Rp1-D gene have the same reaction to Rp1-D-virulent and Rp1-D-avirulent rust

15. Reactions of Rp hybrids

16. Populations of Rp hybrids compared to non-Rp hybrids - inoculated with Rp1-D-virulent rust

17. Rp1-D-virulent isolates - 2001 2001 UI hybrid disease nursery

18. Pairs of Rp hybrids and non-Rp hybrids - inoculated with Rp1-D-virulent rust

19. Pairs of Rp and non-Rp hybrids non-Rp hybridRp hybrid Bodacious Bodacious Rust Day Star Morning Star GG Code 8 GG Code 23 Primetime Prime Plus Sch 5005 Chieftain SS 8102 SS 8102 R

20. Reactions of Rp and non-Rp pairs to Rp1-D-virulent rust 2001 UI Rp hybrid trial

21. no residual resistance • from Rp1-D • no linkage of general • resistance near rp1 region

22. Rp hybrids and non-Rp hybrids - inoculated with a mixture of Rp1-D-virulent and avirulent rust

23. Mixture of virulent and avirulent isolates - 2000 2000 UI hybrid disease nursery

24. Pairs of Rp and non-Rp hybrids Pair 2000 (mix) 2001 (vir) CnS 710 R 15% 34% CnS 710 36% 37% Incredible Rust 10% 29% Incredible 24% 30% Morning Star 22% 34% Day Star 41% 35% Prime Plus 16% 39% Primetime 32% 40%

25. If virulence is frequent Hybrids with Rp1-D have similar reactions as non-Rp hybrids - population distributions alike - Rp and non-Rp versions alike

26. If virulence is infrequent Hybrids with Rp1-D are infected less severely than non-Rp hybrids - additional research on simple ways to detect frequency of virulence and relate frequency to potential severity

27. If virulence is infrequent Rp hybrid non-Rp hybrid

28. Paired hybrid monitor plots non-Rp hybrid Rp hybrid similar number of pustules per leaf- virulence frequent fewer pustules on leaves of Rp hybrid - infrequent

29. Conclusions for Rp1-D are applicable to other Rp genes when virulence against those Rp genes are prevalent Rp-G, Rp1-E, Rp1-I, Rp1-K compound rust genes

30. Fungicides • EBDCs • TILT • strobilurins • (QUADRIS, F-500)

31. Fungicides* • fungicides are preventative • fungicides ARE NOT curative • Rule of thumb: one or two early applications • are superior to multiple late applications • juvenile tissue is more susceptible • infection occurs in the whorl • pustules on lower leaves = inocula for 2o infection • (5,000 urediniospores per pustule) * EBDCs, Tilt

32. Early applications of fungicides ~ 2% severity * EBDCs, Tilt

33. Later applications of fungicides > 5-10% severity * EBDCs, Tilt

34. Strobilurins may change use of fungicides on sweet corn • more efficacious • may have different thresholds ?

37. Thresholds • can rust be controlled if strobilurins • are first applied at higher thresholds? • OR • can strobilurins be applied after we • determined that virulent isolates are • frequent enough to cause severe • infection?

38. Location: Urbana, IL - May 29, 2001 Hybrids: Snow White, Sterling Compounds: Tilt, BASF F-500, Quadris (low, high rate) Application: July 5 (2 to 4-leaf) 5% July 11 (4 to 6-leaf) 15% July 17 (6 to 8-leaf) 30% July 24 (row tassel) 40% 21 treatments

39. 3 replicates, 4-row plots • 27.5 ft length, ~ 40 plants/row • 2 inoculated “spreader” rows • adjacent to each plot • (constant source of urediniospores) • rated rust weekly (severity - %) • harvested 20 consecutive plants/row

40. % yield Rust fungicide trial - 2001

41. % yield Rust fungicide trial - 2001

42. Rust fungicide trial - 2001

43. Non-treated

44. Non-treated

45. strobilurin-treated

46. strobilurin-treated