Optimum Hybrid Maize Breeding Strategies Using Doubled Haploids

Transcription

1 Optimum Hybrid Maize Breeding Strategies Using Doubled Haploids Andrés Gordillo 1,2 and Hartwig H. Geiger 1 1 University of Hohenheim Institute of Plant Breeding, Seed Science, and Population Genetics Stuttgart, Germany 2 AgReliant Genetics LLC, Lebanon, IN 46 th Illinois Corn Breeders School, Champaign, 1 st of March

2 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 46th Illinois Corn Breeders School, Champaign, 1st of March

3 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 an indispensable tool of modern maize research and breeding 46 th Illinois Corn Breeders School, Champaign, 1 st of March

4 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 46 th Illinois Corn Breeders School, Champaign, 1 st of March

5 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 46 th Illinois Corn Breeders School, Champaign, 1 st of March

6 Inbred Inbred A B X X Donor Inducer Inducer In vivo haploid induction in maize F 1 F 1 X Inducer Inducer X About 8-12% of haploid kernels About 10%-15% of haploid kernels Haploid seedlings (n) (n) Treatment with doubling agent Colchicine treatment Doubled haploid plants (n) (2n) Selfing Doubled haploid Doubled haploid lines lines 46th Illinois Corn Breeders School, Champaign, 1st of March

7 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 in the 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 root and coleoptile (e.g. Pl1 in conjunction with B1) 46th Illinois Corn Breeders School, Champaign, 1st of March

8 Haploid-identification markers (2) Red crown marker R1-nj (After Röber 1999) Endosperm Donor (r1-nj Donor r1-nj) Inducer (R1-nj Inducer R1-nj) Embryo Outcrossed or self-pollinated Lethal H embryo F 1 embryo 46th Illinois Corn Breeders School, Champaign, 1st of March

9 Red crown marker R1-nj (3) X Donor Inducer Outcrossed or self-pollinated H embryo F 1 embryo Photo F.K. Röber 46th Illinois Corn Breeders School, Champaign, 1st of March

10 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 46 th Illinois Corn Breeders School, Champaign, 1 st of March

11 Seedling ready for reducing the root and clipping the tip of the coleoptile Photo F.K. Röber 46th Illinois Corn Breeders School, Champaign, 1st of March

12 Transplanting colchicinised juvenile plants into the field Photo F.K. Röber 46th Illinois Corn Breeders School, Champaign, 1st of March

13 DH-line observation nursery Photo W. Schmidt 46th Illinois Corn Breeders School, Champaign, 1st of March

14 Two-stage line development (LD) schemes Year Season Standard scheme Accelerated scheme 1 W L L L L L L L L F 1 inducer 1 S F 1 inducer < H / DH > 2 W < H / DH > T DHL 2 S < DHL > DHL per se DHL per se D 2 TC L 1 T 3 W DHL T DHL T 3 S D 2 TC L 1 T D 2 TC L 2 T 4 4 W S DHL T D 2 TC L 2 T 2 nd -cycle breeding Experimental hybrids 2 nd -cycle breeding Experimental hybrids 46 th Illinois Corn Breeders School, Champaign, 1 st of March

15 Year Season 1 W 1 S 2 W < A B >, < C D >, F 1 H / DH T DHL Inducer Integration of genome-wide selection (GS) 2 S DHL per se TC 1 DHL PS+GS 3 W 3 S Recombination F 1 H/DH Inducer GS 4 W 4 S Recombination F 1 H/DH Inducer GS 46 th Illinois Corn Breeders School, Champaign, 1 st of March

16 Integrated recurrent selection (RS) and parent line development (LD) Year Season 1 W Recombination 1 S Induction RS cycle t 2 W H / DH 2 S DHL per se 3 W DHL T N 0 N 1 3 S TC 1 4 W Recombination RS cycle t+1 4 S Induction 5 W H / DH N RS N 2 n DHL T TC 2 Top lines 5 S DHL per se Experim. hybrids 2 nd cycle breeding 46 th Illinois Corn Breeders School, Champaign, 1 st of March

17 MBP (Version 1.0) Software for optimizing Maize Breeding Plans based on DH lines 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. (Gordillo & Geiger 2008) 46 th Illinois Corn Breeders School, Champaign, 1 st of March

18 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 46 th Illinois Corn Breeders School, Champaign, 1 st of March

19 MBP: Quantitative genetic and operational input variables Estimates of variance components and genetic correlation coefficients Haploid induction parameters Costs of the individual breeding steps All variables are based on data from collaborating breeding companies and can be varied by the user according to his genetic, technical, and financial resources. 46 th Illinois Corn Breeders School, Champaign, 1 st of March

20 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. 46 th Illinois Corn Breeders School, Champaign, 1 st of March

21 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 (N LD = 3) Annual loss of genetic diversity restricted to 2% Gain criterion: I = Grain yield (Qx/Ha) Dry matter content (%) 46 th Illinois Corn Breeders School, Champaign, 1 st of March

22 MBP results: 2. Standard vs. accelerated two-stage LD scheme Scheme Optimum allocation a Genetic gain for yield (kg ha -1 ) N LD N 1 N 2 T 1 T 2 L 1 L 2 per cycle per year Standard (4 ys) Acceler. (3 ys) a N, T, L = Number of DH-lines, testers, and locations, respectively Indices 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 TC vs lines are evaluated per se in the standard vs. accelerated scheme, respectively High-input, short-cycle breeding procedures maximize the genetic gain per year. 46 th Illinois Corn Breeders School, Champaign, 1 st of March

23 MBP results: 3. Standard vs. accelerated 1- and 2-stage RS Annual loss of genetic variance restricted to 2% Scheme 1-stage RS: Genetic gain for yield Optimum allocation (kg ha -1 ) N RS N 1 N 2 T 1 T 2 L 1 L 2 per cycle per year Stand. (3 years) Acceler. (2 years) stage RS: Stand. (4 years) Acceler. (3 years) 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 be recombined to comply with the loss-of-genetic-variance restriction. 46 th Illinois Corn Breeders School, Champaign, 1 st of March

24 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% Genetic gain for yield (kg ha -1 ) Optimum allocation per year w RS : w LD N RS N LD N 1 N 2 T 1 T 2 L 1 L 2 G RS P LD 0 : : : Weights given to RS and LD, respectively, considerably influence the optimum allocation but hardly affect the maximal genetic gain per year. 46 th Illinois Corn Breeders School, Champaign, 1 st of March

25 MBP results: 5. Influence of population size on the long-term progress in line development Cummul. selection gain for yield [kg ha -1 ] Number of recombined lines N rec = 10 (Δσ 2 g = 7.1%) N rec = 15 (Δσ 2 g = 4.5%) N rec = 30 (Δσ 2 g = 2.1%) No. of hybrid parent lines selected per cycle: N LD = No. of selection cycles 46 th Illinois Corn Breeders School, Champaign, 1 st of March

26 Relative importance of recurrent selection and parent line development Performance 1 PLD cycle = 4 yrs TC 2 TC 1 n RU RU D H / DH 1 L TC 1 H / DH TC 2 n TC RU 1 H / DH n TC 2 D 1 L D 1 L RU H / DH 1 RS cycle = 3 yrs Time 46 th Illinois Corn Breeders School, Champaign, 1 st of March

27 Summary and Conclusions (1) In vivo techniques of haploid induction have become standard tools in maize breeding and research. Major advantages of DH lines in hybrid breeding include maximum genetic variance from the very first generation perfect compliance with DUS criteria short time to market simplified logistics reduced expenses for selfing and maintenance breeding. 46 th Illinois Corn Breeders School, Champaign, 1 st of March

28 Summary and Conclusions (2) Genome-wide selection can effectively be integrated in DH-line based breeding schemes. A software package MBP (version.1.0) has been developed to optimize the allocation of breeding resources and to determine the relative merits of alternative breeding schemes. High-input, short-cycle, breeding schemes are expected to provide maximal annual genetic gain. 46 th Illinois Corn Breeders School, Champaign, 1 st of March

29 Summary and Conclusions (3) The long-term genetic gain in LD builds up on the cumulative genetic gain from RS. It is advisable to weight RS higher than LD when optimizing combined RS/LD breeding schemes Increasing the weight for RS leads to a considerable increase in the gain from RS, while it hardly affects the gain 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 shortcycle (accelerated) schemes! 46 th Illinois Corn Breeders School, Champaign, 1 st of March

30 Acknowledgements German Bundesministerium für Wirtschaft und Arbeit BMWA (AiF grant No ) 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) 46 th Illinois Corn Breeders School, Champaign, 1 st of March