optimum hybrid maize breeding strategies using doubled...

46th Illinois Corn Breeders School, Champaign, 1st of March 2010 1

Andrés Gordillo1,2 and Hartwig H. Geiger1

1University of Hohenheim

Institute of Plant Breeding, Seed Science, and Population Genetics

70593 Stuttgart, Germany

2AgReliant Genetics LLC, Lebanon, IN

Optimum Hybrid Maize Breeding Strategies Using Doubled Haploids


Outline

• Introduction

• In vivo induction of maternal haploids

• DH-line based breeding schemes

• Software MBP for optimizing the allocation of breeding resources- Features- Selected results

• Summary and conclusions


Applications of the DH technology

• Marker-trait association studies

• Marker-aided introgression of genes

• Genetic engineering

• Molecular cytogenetics

• Hybrid breeding

The DH technology has become anindispensable tool of modern maize research and breeding


Advantages of DH lines in hybrid breeding

• Maximum genotypic variance in line-per-se and testcross trials

• High reproducibility of early-testing results

Increased selection gain

• Complete homozygosity from the very first generation

Perfect compliance with DUS criteria for variety protection, short “time to market”

Reduced nursery expenses, simplified logistics Facilitates marker-assisted selection and

backcrossing


In vivo induction of maternal maize haploids

For review see Geiger (2009) in Handbook of Maize. Springer, New York

• Pollination of maize plants with specific genotypes called inducers, which leads to kernels with a haploid embryo and a regular triploid endosperm

• Widely used for line development in commercial hybrid maize breeding

• Increasingly used in research

• Only moderate influence of donor genotype and induction environment compared to in vitro haploid induction


About 10%-15% of haploid kernels

InbredA

InbredB

X X

X

Inducer

XF1 Inducer

Colchicinetreatment

Haploid seedlings (n)

Doubled haploid plants (2n)

Selfing

Doubled haploid lines

Donor

In vivo haploid induction in

maize

About 8-12% of haploid kernels

Treatment with doubling agent

Selfing

Haploid seedlings (n)

Doubled haploid plants (n)

Doubled haploid lines

InducerF1

InducerDonor

Inbred A

Inbred B


Haploid-identification markers (1)

Markers expressed before chromosome doubling

Dominant grain color marker gene R1-nj(in conjunction with mutant pigmentation genes A1 or A2, and C2)

Causes pigmentation in the aleurone (endosperm) and inthe scutellum (embryo tissue)

Needs donor with colorless seeds

Expression may be suppressed by inhibitor genes (e.g. C1-I)…carried by the female parent

• Dominant color marker genes expressed in the primary rootand coleoptile (e.g. Pl1 in conjunction with B1)


Haploid-identification markers (2)

„Red crown“ marker R1-nj

Endosperm

Embryo

H embryo F1 embryoLethalOutcrossed or self-pollinated

Donor InducerDonor

(r1-nj r1-nj)Inducer

(R1-nj R1-nj)

(After Röber 1999)


Outcrossed or self-pollinated

InducerDonor

X

„Red crown“ marker R1-nj (3)

H embryo F1 embryoPhoto F.K. Röber


Chromosome doubling

• Immersion of seedlings in colchicine (Gayen et al. 1994,Deimling et al. 1997, Eder and Chalyk 2002)

70 – 80% of the seedlings survive 10 – 40% of the surviving plants produce selfed seed

• Due to high toxicity of colchicine, most breeding companies are interested in less hazardous substances

Herbicides, e.g. Pronamid, APM, Trifluralin, Oryzalin

Nitrous oxide gas (Kato 2002)

-> not suited for large-scale haploid induction

1146th Illinois Corn Breeders School, Champaign, 1st of March 2010

Seedling ready for reducing the root and clipping the tip of the coleoptile

Photo F.K. Röber


Transplanting colchicinised juvenile plants into the field

Photo F.K. Röber

1346th Illinois Corn Breeders School, Champaign, 1st of March 2010

DH-line observation nursery

Photo W. Schmidt


Season

Experimental hybrids

2nd-cycle breeding

F1 inducer

< H / DH >

× T

D2L • T

DHL × T’

D2L • T’

L×L’ L’’×L’’’…

L >

W

W

W

W

S

S

S

S

1

2

3

4

1

4

2

3

F1 inducer

< H / DH >

DHL per se

DHL× T

TC1

× T’

TC2

L×L’ L’’×L’’’…

< DH

W

W

W

W

S

S

S

S

Standard schemeYear

Experimental hybrids

2nd-cycle breeding

F1 inducer

< H / DH >

D2L • T

× T’

D2L • T’

L×L’ L’’×L’’’…

F1 inducer

< H / DH >

T × DHL

TC1

DHL× T’

TC2

Accelerated scheme

DHL per se

Two-stage line development (LD) schemes


Integration of genome-wide selection (GS)

Year Season

1 W

1 S

2 W

2 S

3 W

3 S

F1 Inducer

H / DH

T × DHL

TC1DHL per se

Recombination

F1 Inducer

Recombination

F1 Inducer

4 W

4 S

GS

GS

PS+GS

GS

GS

DHL

H/DH

H/DH

< A × B >, < C × D >, …

Year Season

1 W

1 S

2 W

2 S

3 W

3 S

F1 Inducer

H / DH

T × DHL

TC1DHL per se

Recombination

F1 Inducer

Recombination

F1 Inducer

4 W

4 S

GS

GS

PS+GS

GS

GS

DHL

H/DH

H/DH

< A × B >, < C × D >, …


1 W Recombination

1 S Induction

2 W H / DH

2 S DHL per se

3 W DHL T

3 S TC1

4 W Recombination

4 S Induction

5 W H / DH

5 S DHL per se

DHL T’

TC2

Top lines

Experim. hybrids

2nd cycle breeding

RS

cycl

e t

RS

cycl

e t+

1

N0

N1

NRS N2

n

Integrated recurrent selection (RS) and parent line development (LD)

Year Season


• Maximizes the expected genetic gain per year for a given annual budget and a limited relative annual loss of genetic variance.

• Allows to optimize 1-, 2-, and 3-stage testcross selection procedures for alternative breeding schemes.

• Allows the user to specify the tester type (e.g. pure line, single cross, population) for each testcross selection stage separately.

• Accounts for detailed monetary costs of each individual breeding step.

MBP (Version 1.0)Software for optimizing Maize Breeding Plans based on DH lines

(Gordillo & Geiger 2008)


MBP is applicable to :

• Line development (LD) in hybrid breeding

• Recurrent selection (RS)

• Integrated RS/LD approaches

RS is treated as an integral part of LD

• Interlinking successive staggered breeding cycles


• Estimates of variance components and genetic correlation coefficients

• Haploid induction parameters

• Costs of the individual breeding steps

All variables are based on data from collaboratingbreeding companies and can be varied by the useraccording to his genetic, technical, and financialresources.

MBP: Quantitative genetic and operational input variables


MBP: Gain criterion

The gain criterion is the expected genetic gain in

GCA for an index composed of the testcross

performance for grain yield and dry matter content.

Arbitrary index weights may be chosen by the user.


Selected MBP results: 1. General program specifications

• Annual budget: US $ 750,000

• Proportion of lines pre-selected for per se performance: 50%

• Single-cross tester(s) at all selection stages

• Yield trials: multiple locations, unreplicated

• Three finally selected lines per LD cycle (NLD = 3)

• Annual loss of genetic diversity restricted to 2%

• Gain criterion:

I = Grain yield (Qx/Ha) + 2.5 Dry matter content (%)


MBP results: 2. Standard vs. accelerated two-stage LD scheme

a N, T, L = Number of DH-lines, testers, and locations, respectivelyIndices refer to test stages 1 and 2

Note: In the Accelerated Scheme, the per se evaluation of DH lines is not before but in parallel to the TC1

7146 vs. 5680 lines are evaluated per se in the standard vs. accelerated scheme, respectively

High-input, short-cycle breeding procedures maximize the genetic gain per year.

Scheme Optimum allocationa Genetic gain for yield (kg ha-1)

NLD N1 N2 T1 T2 L1 L2 per cycle per yearStandard(4 ys) 3 3573 57 1 7 5 20 812 203

Acceler.(3 ys) 3 5680 79 1 6 3 19 786 262


MBP results: 3. Standard vs. accelerated 1- and 2-stage RS

Annual loss of genetic variance restricted to 2%

The accelerated version is more efficient than the standard scheme.

One-stage RS is superior to two-stage RS.

In the most efficient RS scheme more than 50 DH lines need to berecombined to comply with the loss-of-genetic-variance restriction.

Scheme Optimum allocation Genetic gain for yield (kg ha-1)

NRS N1 N2 T1 T2 L1 L2 per cycle per year1-stage RS:

Stand. (3 years) 43 2481 - 2 - 6 - 504 168Acceler. (2 years) 57 3900 - 1 - 8 - 442 210

2-stage RS:

Stand. (4 years) 32 3821 225 1 3 4 12 624 156Acceler. (3 years) 39 5574 274 1 3 3 12 576 192


MBP results: 4. Integrated RS/LD standard breeding scheme; influence of the weights for RS and LD

• One-stage testcrossing in RS• Two-stage testcrossing in LD• Annual loss of genetic variance restricted to 2%

Weights given to RS and LD, respectively, considerably influence the optimum allocation but hardly affect the maximal genetic gain per year.

Genetic gain for yield (kg ha-1)

Optimum allocation per yearwRS : wLD NRS NLD N1 N2 T1 T2 L1 L2 GRS PLD

0 : 1 34 3 3573 57 1 7 5 20 143 204

0.5 : 0.5 32 3 3805 153 1 4 4 14 155 202

1 : 0 32 3 3831 225 1 3 4 12 156 199


MBP results: 5. Influence of population size on the long-term progress in line development

0

1000

2000

3000

4000

5000

6000

0 1 2 3 4 5 6 7 8 9 10

Nrec = 10 (Δσ2g = 7.1%)

Nrec = 15 (Δσ2g = 4.5%)

Nrec = 30 (Δσ2g = 2.1%)

Cum

mul

. sel

ectio

n ga

in fo

r yie

ld [k

g ha

-1]

No. of selection cycles

No. of hybrid parent lines selected per cycle:

NLD = 3

Number of recombined lines


Relative importance of recurrent selection and parent line development

RU

H / DH

D1LTC1

RU

H / DH

D1LTC1

RU

H / DH

D1LTC1

RU

H / DHTC2

TC2

TC2

1 RS cycle = 3 yrs

1 PLD cycle = 4 yrsn

n

n

RU

H / DH

D1LTC1

RU

H / DH

D1LTC1

RU

H / DH

D1LTC1

RU

H / DHTC2

TC2

TC2

1 RS cycle = 3 yrs

1 PLD cycle = 4 yrsn

n

n

Perf

orm

ance

Time


Summary and Conclusions (1)

• In vivo techniques of haploid induction have becomestandard tools in maize breeding and research.

• Major advantages of DH lines in hybrid breedingincludemaximum genetic variance from the very first

generationperfect compliance with DUS criteriashort time to marketsimplified logistics reduced expenses for selfing and maintenance

breeding.



• Genome-wide selection can effectively be integrated in DH-line based breeding schemes.

• A software package “MBP (version.1.0)” has beendeveloped to optimize the allocation of breedingresources and to determine the relative merits ofalternative breeding schemes.

• High-input, short-cycle, breeding schemes are expected to provide maximal annual genetic gain.



• The long-term genetic gain in LD builds up on thecumulative genetic gain from RS.

It is advisable to weight RS higher than LD whenoptimizing combined RS/LD breeding schemes

• Increasing the weight for RS leads to a considerableincrease in the gain from RS, while it hardly affects thegain in LD.

• Sizable numbers of selected DH-lines need to be recombined to preserve enough genetic diversity for subsequent breeding cycles, especially in case of short-cycle (accelerated) schemes!


Acknowledgements

• German Bundesministerium für Wirtschaft und Arbeit BMWA (AiF grant No. 13991)

• Gemeinschaft zur Förderung der privaten deutschen Pflanzenzüchtung e.V. (GFP)

• Südwestdeutsche Saatzucht GmbH & Co. KG (SWS)

• Monsanto Agrar Deutschland GmbH

• KWS SAAT AG

• F. K. Röber (SWS)

• E. Holzhausen (Monsanto)

• M. Ouzunova and W. Schmidt (KWS)

• G. Seitz (AgReliant)

• S. Koch (University of Hohenheim)

optimum hybrid maize breeding strategies using doubled...

Documents