Improving the use of genes for septoria resistance in wheat varieties

Transcription

1 Improving the use of genes for septoria resistance in wheat varieties James Brown and Lia Arraiano John Innes Centre, Norwich, UK Phone

2 Septoria tritici blotch Mycosphaerella graminicola Splash-borne hemibiotrophic fungus The major disease of wheat in Europe

3 Need for elite resistant varieties Modern varieties : wide variation for resistance 2001 : Resistance to strobilurin (QoI) fungicides Recently : Emerging resistance to triazoles? Increased demand for varieties which combine: High and reliable yield Marketable quality Adequate resistance to septoria Many breeders say they have found it hard to combine good septoria resistance with high yield

4 The context of disease research

5 Aims of JIC s septoria research What resistance genes are in UK varieties? What contribution do they make to disease control in field situations? Do breeders have enough R-genes? How does selection for septoria resistance affect breeding for other traits?

6 First LINK project 226 wheat varieties Varieties in UK Recommended List in late 1990 s + progenitors back to 1860 s some very susceptible to yellow rust 11 field trials Scored septoria on upper leaves Septoria scores adjusted for Height and related traits: Short stature > more septoria (Heading date) Earlier leaf emergence > more septoria at time of scoring = Disease escape

7 Correlation of septoria with height Septoria Resistant Susceptible Height (cm)

8 Correlation of septoria with heading Septoria (logit transformation) Heading date (from 1st May)

9 Septoria resistance genes Major genes Stb6 on chr 3A (43/226, inc. many resistance sources) Stb15 on chr 6A (142/226, inc. Longbow, Riband ) Less common : Stb7, Stb9, Stb10, Stb11, Stb12 Uncharacterised genes in Chaucer, Equinox, Wembley Partial resistance Polygenic / Oligogenic Arina : no QTL identified (lots of minor genes?) Exsept : most resistance explained by few QTLs Susceptibility gene on chr arm 5BS of Hobbit sib Familiar pattern from mildew & rusts In which major genes have no durable value

10 Contributions of R-genes R & escape Factor df Var. ratio F prob. Effect on STB Height to flag leaf <0.001 Reduces Leaf erectness <0.007 Reduces Res <0.001 Reduces Including pedigree as random effect in REML analysis Height to flag leaf < Reduces Res < 0.01 Reduces Res < 0.02 Reduces Res < Reduces Effect of leaf erectness is a chance association in pedigree

11 Stb genes and field resistance Res-1 Susc-1 Res-2 Susc-2 23% less Septoria in varieties with Res-1 33% less Septoria in varieties with Res-2

12 QTL analysis of partial resistance NB: much PR is polygenic and most QTLs cannot be detected in normal-sized populations 98 ex 226 varieties genotypes with 121 SSRs 10 markers linked to septoria response (P<1%) Not considering pedigree Fitting pedigree as random effect 6 QTL on different chromosomes Resistance allele of 1 QTL mostly in spring wheat Others present in winter wheat, including Res-1

13 Association of STB with markers Susceptible 0 S_allele 1 S_allele 2 R_allele 1 R_allele 2 0 R_allele S_allele 1 S_allele Septoria level in the field Resistant % less Septoria on average in varieties with R_alleles (P<0.001) 54% less Septoria on average in varieties with R_allele (P<0.001)

14 Yield data NIAB NL & RL : fungicide treated Yield in absence of disease Yield (tons / hectare) Thousand grain weight 70 wheat varieties with septoria data Yield affected by Year of release % grain protein Yield (t/ha) Yield (t/ha) Year Grain protein %

15 Correlation of septoria with yield Yield (adj. for Year, Prot, TGW) Septoria (adjusted for Height)

16 Best-fitting model of yield Factor Sum of F prob Partial corr n squares with yield Year < % protein 4.39 < TGW 0.61 < Septoria Conclusion: Selection for yield causes unintentional selection for susceptibility to septoria

17 Second LINK project Key aim = investigate association between septoria and yield Effect of septoria resistance in general? Or of specific septoria resistance genes? Association genetics analysis 2-3 QTLs associated with correlation between yield + septoria 3-4 QTLs not associated

18 Genetics of yield and septoria Senat x Savannah : 104 DH lines Septoria data : from Sejet Planteforædling Yield trials : 2004/5 and 2005/6 1 QTL for resistance not linked to reduced yield 1 resistance QTL maps close to reduced TGW Spark x Rialto : 130 DH lines Septoria trials : 2005/6 Yield data : from John Snape & colleagues 1 QTL for resistance not linked to reduced yield 2 resistance QTLs map near reduced yield or yield components Both crosses Phenotypic correlation of septoria with yield & TGW

19 Strategy for breeding Plenty of septoria resistance in UK wheats No need for exotic introductions if full range of resistance genes is used Some resistance capable of marker-assisted selection but most not Should be possible to break link between resistance and yield Effective field selection for two traits separately + MAS for most useful QTLs Select against high susceptibility Maintaining selection for other (more) important traits

20 No cost of mildew resistance Yield (adj'd for Year & Protein) Mildew (logit)

21 Acknowledgements Lia Arraiano (everything!) Laetitia Chartrain & Penny Brading (major genes) Gloria Solares Diaz (yield / septoria analysis) Jane Kirby (JIC Genome Lab: SSR analysis) Collaborators: John Snape & colleagues (JIC: Spark x Rialto yield data) Gert Kema & Els Verstappen (Wageningen : major genes) Clare Leaman & colleagues (NIAB : variety yield data) Plant breeders: Simon Berry, Jeremy Widdowson, Stephen Smith, David Feuerhelm, Paul Fenwick, Chris Chapman, Lars Eriksen, Thilo Hammann, Nick Balaam, Phil Howell, Fermin Azanza (septoria & yield trials)

22 Acknowledgements