This document summarizes research mapping durable adult plant resistance to stem rust in wheat. Nine consistent and five inconsistent quantitative trait loci (QTLs) were detected across six mapping populations. A QTL on chromosome 3BS was found in all parents and is linked to resistance gene Sr2. A QTL on chromosome 7DS confirms the involvement of gene Lr34. A QTL on chromosome 1BL suggests the involvement of gene Lr46. These QTLs in combination with Sr2 form the "Sr2-Complex" conferring durable adult plant resistance. Future work will include fine mapping of QTLs and pyramiding adult plant resistance with major genes using markers.

1. Mapping of durable adult plant stem rust resistance to Ug99 and its racesS. Bhavani, R. P. Singh, S. Singh, J. Huerta, O. Argillier, S. Brun, S. Lacam, N. Desmouceaux, P. Njau and R. Wanyera

2. Ug99-Global threatWide virulence range and highly aggressive

3. Threat to significant proportion of global wheat germplasm > 80% susceptible

4. New races in Ug99 (TTKSK) lineageUg99+Sr24 Virulence (2006)-TTKSTUg99+Sr36 Virulence (2007)-TTTSKOther races-TTKSF,TTKSP, PTKSK,PTKSTVirulence spectrum of Ug99 (TTKSK)

5. Types of Resistance≈ Race-specific ≈ Major genes ≈ HypersensitiveMonogenic(Boom & Bust) Pyramiding≈ Race-nonspecific ≈ Minor genes ≈ Slow rusting/ PartialPolygenic(Durable)

6. Focus towards durable resistance?Multiple races of rust pathogens

7. Mutating and migrating nature of rust pathogens

8. Several race-specific genes ineffective in one ormore wheat growing regionsMaintaining host genetic diversity

9. Preventing epidemics – reducing yield lossesCharacteristics of slow rusting resistance Minor genes with small to intermediate effectsGene effects are usually additiveResistance does not involve hypersensitivitySusceptibility at seedling stageGenes confer slow disease progress through:Reduced infection frequency- Receptivity

10. Lower disease severity, Increased latent period

11. Small to large compatible pustules on stems

12. Reduced spore productionAccumulating minor genes - Near immunity % RustSusceptible 100801 to 2 minor genes 602 to 3 minor genesMunal, Picaflor,Francolin, Pauraque40204 to 5 minor genesKingbird020010305040Days data recordedRelatively few additive genes, each having small to intermediate effects, required for satisfactory disease control

13. Sr2-Complex for durable APR(Sr2 + other minor genes for durable resistance to stem rust)Sr2 transferred to wheat from ‘Yaroslav’ emmer in 1920s by McFadden and linked to pseudo-black chaff (~ 90years)

14. Sr2 still provides moderate levels of resistance in Kenya (~30% reduction in disease severity)

15. Seedling and APR genes with intermediate effects in combination with Sr2 produce enhanced levels of resistance

16. Formed the basis of durable resistance historically in some CIMMYT wheatsPyramiding-APR+ Major genesStem rust severities of SrTmp (n=125) and SrSha7 (n=66) possessing wheat lines in Kenya 2010 APR genes enhance the expression of moderately effective race-specific genes

17. Identifying materials with adult plant resistance to Ug99KingbirdGreenhouse seedling tests -USDA-ARS Lab. in St. Paul, Minnesota, USAField evaluations-Kenya/EthiopiaCharacterization of PBC phenotype and Sr2 linked molecular markersIdentified APR Sources: Kingbird, Kiritati, Juchi, Pavon, Huirivis#1, Muu, Kenya Swara, Kenya Kudu, Parula, Picaflor, Danphe, Chonte

18. Mapping of Adult Plant Resistance to Stem Rust15 RIL mapping populations developed and phenotyped in Kenya for at least 2 seasons

19. Genetic studies suggest the involvement of 3 or 4 minor genes in each resistant parent

20. Initial molecular mapping of six populations completed

21. Other populations being assigned to graduate students MethodologyPhenotyping conducted in 2009, 2010 field seasons

22. Artificial epidemics with Ug99+Sr24 (TTKST)

23. SR severity recorded when 80-100% disease on most susceptible RILs- Modified Cobb scaleDArT and SSR markers

24. Inclusive Composite Interval Mapping (ICIM), Q-gene, QTL Cartographer

25. ICIM- http://www.isbreeding.net/

26. Increased power of detection

27. Additive and Epistatic Effects

28. LOD Scores>2.5, Probability in step wise regression 0.001

29. User friendlyPBW343 X KingbirdKingbirdPBW343

30. PBW343 X Kingbird5B1A3BS7AL7DSPBC

31. PBW343 X KiritatiKiritatiPBW343

32. PBW343 X Kiritati7DS3BS2D5BS

33. PBW343 X JuchiJuchiPBW343

34. PBW343 X Juchi2BS3BS4AS5BL6BS

35. Avocet X Pavon 76 (RILs without Sr26)Pavon 76

36. Avocet X Pavon 763BS2BS1BL6BS3D5A

37. PBW343 X Huirivis#1Huirvis#1PBW343

38. PBW343 X Hurivis#13BS2BS5BLPBC5D

39. PBW343 X MUUMuuPBW343

40. PBW343 X MUU3BS2BS5BL

41. Inconsistent QTLs4BS-Kingbird2A-Kingbird2D-Kiritati5A-Pavon5DS-Hurivis#1

42. QTLs summaryIn total 9 consistent and 5 inconsistent QTLs detected in six mapping populations

43. QTL on chromosome 3BS in all parents is linked to resistance gene Sr2 & PBC

44. QTL on chromosome 7DS in Kingbird and Kiritaticonfirms the involvement of Lr34 in reducing stem rust severity (Lr46/Yr29/Pm39 )QTL on chromsome1BL in Pavon 76 and PBW343 suggests the involvement of Lr46 in reducing stem rust severity (Lr34/Yr18/Pm38)

45. 7 new QTLs identified on chromosomes 1A, 2B, 3D, 4A, 5B, 6B and 7A

46. 5 inconsistent QTLs identified on chromosomes 2A, 2D, 4B, 5A and 5D

47. These QTLs in combination with Sr2form the “Sr2-Complex”Future outlookSaturating genomic regions with additional markers for fine mapping

48. Development of PCR based assays for flanking markers

49. Pyramiding APR + major genes using markers

50. Cloning for resistance gene cassettesAcknowledgementsAgencies supporting rust research:Bill and Melinda Gates Foundation through: DRRW ProjectSyngenta Foundation

51. Grain Research and Development Corporation (GRDC), Australia

52. Kenya Agricultural Research InstituteTHANK YOU