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. Rust severity % and (estimated Reactions of sweet corn hybrids yield reductions)**RMRMMSS 0-10% (3%)0.630.260.110.110.11 10-20% (9%)0.370.470.160.110 20-30% (15%) 00.260.630.260.16 30-40% (21%)000.110.320.26 40-50% (27%)0000.210.32 >50% (>30%)00000.16 * 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 Probability* of severe rust

7. Susceptible Rp-resistant

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

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

10. 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? Questions about the Rp1-D-virulent race

11. Reactions of non-Rp hybrids

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

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

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

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 hybrid Rp 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 R15%34% CnS 71036% 37% Incredible Rust10%29% Incredible24%30% Morning Star22%34% Day Star41%35% Prime Plus16%39% Primetime32%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 2 o 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. Rust fungicide trial - 2001 % yield

41. Rust fungicide trial - 2001 % yield

42. Rust fungicide trial - 2001

43. Non-treated

45. strobilurin-treated

57. Rust fungicide trial - 2001 Sterling

60. yield was reduced about 4% to 6% for each 10% rust severity Snow White one application of strobilurin at 5%, 15% or 30% gave about the same level of control as weekly applications of Tilt Sterling applications at 15% and 30% did not control as well as applications at 5%, but yield did not differ between applications at 5% and 15%

61. Application thresholds for strobilurins may be high enough to determine whether or not Rp1-D-virulent rust is frequent enough or cause damage. Thresholds for strobilurins probably will be in the 5% to 15% range. Tentative conclusions

62. general or partial resistance susceptible

63. Common rust field corn vs. sweet corn - 2000 Field corn 1573 field corn lines x FR 1064 1 replicate 1 to 9 scale (~sq. rt. of %) PI accessions - 2001 2000 accessions (So. America) 2 replicates 1 to 9 scale (~sq. rt. of %)

64. Common rust - 2000 sweet corn vs. field corn Severity (%) or 1 to 9 rating (squared)

66. Antioquia, ColumbiaAncash, Peru Boyaca, ColumbiaApurimac, Peru Cauca, ColumbiaCajamarca, Peru Lima, Peru Junon, Peru B93 (PI 539871) B108 (PI 597926) IA DS61* (NSL 75976) * source of resistance to P. polysora Sources of accessions with partial rust resistance?

67. Early CogentHawaii #9 Silver Sucro EsteemLancelot Sugar 73 GG Code 27Miracle Sugar 74 bt GG Code 61PX 9314639 Tendertreat EH GG Code 74Seneca Horizon Partial rust resistance in active* sweet corn hybrids ChampGG Code 6 Sensor GH 2757Merlin Tuxedo

68. AVX 2539Sugar TimeSweetie 82 Dinner TimeSun 2577SS 8801 GG Code 14Sun 2642Tastee Treat Prime PakSun 2733 WH 3125 Sugar LoafSweetie 76Wintergreen Partial rust resistance in inactive* sweet corn hybrids

69. Rp genes fungicides general resistance

70. Jerald Pataky Department of Crop Sciences University of Illinois j-pataky@uiuc.edu www.sweetcorn.uiuc.edu