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Strategies for Major Genes One gene at a time Gene rotation Gene “ pyramids ” Mixtures Regional deployment Working With Minor Genes. Minor Gene Resistance Often multiple gene inheritance Often recessive Usually gives incomplete resistance Can be more complicated to work with

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slide1
Strategies for Major Genes One gene at a time

Gene rotation

Gene “pyramids”

Mixtures

Regional deployment

Working With Minor Genes

slide2
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
minor gene resistance
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
estimating number of genes and hertitability
Estimating Number of Genes and Hertitability
  • Statistical, quantitative genetic approaches
  • QTL approaches
  • Both give same answer
minor gene resistance1
Minor Gene Resistance

Commonly only 2-4 genes identified

Often 1 or 2 that contribute majority of effect

Heritability usually moderate to high

estimating number of genes and hertitability1
Estimating Number of Genes and Hertitability
  • Statistical, quantitative genetic approaches
  • QTL approaches
  • Both underestimate gene number
  • Both depend on population size
barley stripe rust
Barley Stripe Rust

Pop. Size Number of QTL

50 3

100 4

150 5

200 5.5

300 6

409 8

barley stripe rust1
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
components of resistance
Components of Resistance

Length of latent period

Infection efficiency

Lesion size

Sporulation rate

Length of infectious period

selection based on components of resistance
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

slide12
Can be relatively easy to

maintain minor gene

resistance once you

have it

slide14
Use of Top Crosses to Maintain Minor Genes for Stripe Rust Resistance While Improving Other Traits
effects of interplot interference uredia tiller
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

test with single race or multiple races
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

slide20

Percent of Willamette Valley Winter Wheat Acreage Planted to ‘Foote’

Year Percent

2001 22

2002 50

2003 50

2004 51

2005 32

2006 4

slide21
Lessons:

The Vertifolia Effect can be real

“Perfect Storms” do happen

molecular breeding
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
slide27
Strategies for Major Genes One gene at a time

Gene rotation

Gene “pyramids”

Mixtures

Regional deployment

Working With Minor Genes

single gene at a time use it till you lose it
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

rotating genes
Rotating Genes
  • Likely a disaster
  • Virulence unlikely to decline to previous levels
pyramids or combinations of major genes
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
mixtures or blends of major genes
Mixtures or Blends of Major Genes
  • Can be highly effective
  • Should be considered more often
  • Results variable, empirical testing critical
regional deployment
Regional Deployment
  • Likely very useful if done
  • Is it feasible?
minor gene resistance2
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
don t forget about ipm
Don’t Forget About IPM

Potato late blight severity:

Susceptible, no fungicide = 100%

Weekly fungicide = 56%

Minor gene resistance = 46%

Resistance + fungicide = 9%