Strategies for Major Genes One gene at a time Gene rotation Gene “ pyramids ” Mixtures

1. Strategies for Major Genes One gene at a time Gene rotation Gene “pyramids” Mixtures Regional deployment Working With Minor Genes

2. Minor Gene Resistance • Often multiple gene inheritance • Often recessive • Usually gives incomplete resistance • Can be more complicated to work with • Not highly specific • Tends to be stable over time

3. Minor Gene Resistance • Often more available than we think • Simply purging the most susceptible material can be very useful • Inheritance is much less complex than once thought

4. Estimating Number of Genes and Hertitability • Statistical, quantitative genetic approaches • QTL approaches • Both give same answer

5. Minor Gene Resistance Commonly only 2-4 genes identified Often 1 or 2 that contribute majority of effect Heritability usually moderate to high

6. Estimating Number of Genes and Hertitability • Statistical, quantitative genetic approaches • QTL approaches • Both underestimate gene number • Both depend on population size

7. Barley Stripe Rust Pop. Size Number of QTL 50 3 100 4 150 5 200 5.5 300 6 409 8

8. Barley Stripe Rust • Number of QTL increased with population size • ID QTL with biggest effect with small population size • ID additional QTL with smaller effects with larger population size

9. Components of Resistance Length of latent period Infection efficiency Lesion size Sporulation rate Length of infectious period

10. Selection Based on Components of Resistance Components tend to be highly correlated More recent evidence suggests that components are pleiotropically controlled Example of barley stripe rust

12. Can be relatively easy to maintain minor gene resistance once you have it

13. Stripe Rust Puccinia striiformis VIDAL L., INRA

14. Use of Top Crosses to Maintain Minor Genes for Stripe Rust Resistance While Improving Other Traits

15. Stuff Happens XXXX

16. Effects of Interplot Interference (uredia/tiller) Isolated Adjacent t Cultivar 3x4 m 2x2 m 1/4x1 m L98 1000 500 2300 Sultan 750 250 1700 Volla 110 40 700 Julia 17 12 450 Vada 1 15 130 Range 1000X 42X 18X

17. Test with Single Race or Multiple Races? No. races No. of to which lesions Cultivar resistant per cm2 Zenith 64 2 Kataktara 55 14 Kano 51 40 39 Lacrosse 19 66 KTH 4 94

18. Vertifolia Effect

20. Percent of Willamette Valley Winter Wheat Acreage Planted to ‘Foote’ Year Percent 2001 22 2002 50 2003 50 2004 51 2005 32 2006 4

21. Lessons: The Vertifolia Effect can be real “Perfect Storms” do happen

22. QTL Analysis and MAS

23. Source: CAST

25. QTL Analysis and MAS

26. Molecular Breeding • Biology and engineering are very different • High-quality phenotyping is still the most important ingredient of a resistance breeding program, and this likely will always be so

27. Strategies for Major Genes One gene at a time Gene rotation Gene “pyramids” Mixtures Regional deployment Working With Minor Genes

28. Single Gene at a Time“Use It Till You Lose it” • May be needed as a stop-gap measure • In general, don’t go there - Puts growers at risk - Disruptive to breeding programs

29. Rotating Genes • Likely a disaster • Virulence unlikely to decline to previous levels

30. Pyramids or Combinations of Major Genes • Useful in increasing durability of major genes • More complex than using single genes • Takes time to determine which combinations work best

31. Mixtures or Blends of Major Genes • Can be highly effective • Should be considered more often • Results variable, empirical testing critical

32. Regional Deployment • Likely very useful if done • Is it feasible?

33. Minor Gene Resistance • It’s hard to go wrong with this approach • May take a bit more effort up front • Likely to eliminate a lot of headaches in the longer term

34. Tolerance

35. Don’t Forget About IPM Potato late blight severity: Susceptible, no fungicide = 100% Weekly fungicide = 56% Minor gene resistance = 46% Resistance + fungicide = 9%

36. Stuff Happens XXXX