Download presentation
Presentation is loading. Please wait.
1
Plant Breeding – an Overview
2
Objective 1: know basic plant genetics and breeding terminology
3
Gamete A mature reproductive cell that is specialized for sexual fusion Haploid (n) Containing only one set of chromosomes (n). Each gamete is haploid Cross A mating between two individuals, leading to the fusion of gametes Diploid (2n) Two copies of each type of chromosome in the nuclei, formed by the fusion of two gametes Zygote The cell produced by the fusion of the male and female gametes
4
Gene The inherited segment of DNA that determines a specific characteristic in an organism Locus The specific place on the chromosome where a gene is located Alleles Alternative forms of a gene
5
Genotype The genetic constitution of an organism Homozygous An individual whose genetic constitution has both alleles the same for a given gene locus (eg, AA) Heterozygous An individual whose genetic constitution has different alleles for a given gene locus (eg, Aa)
6
Homogeneous A population of individuals having the same genetic constitution (eg, a field of pure-line soybean; a field of hybrid corn) Heterogeneous A population of individuals having different genetic constitutions Phenotype The physical manifestation of a genetic trait that results from a specific genotype and its interaction with the environment
7
What is Plant Breeding? The genetic adjustment of plants to the service of humankind ---Sir Otto Frankel Source:
8
Objective 2: know why plant breeding is important and useful
Several examples in soybean
9
Why Plant Breeding Increased global human population (shown here in billions of people) will lead to increased demand for food, fiber and energy: improving plant genetics is one tool Adapted from
10
Plant Breeding Targets
1. Yield Source: USB photo disc 0976
11
Plant breeding has contributed to more than 50% of increased USA crop productivity during the last 30 years Source:
12
Plant Breeding Targets
Improved product quality Source:
13
H H C C Hydrogenation: flavor and oxidative stability
Trans fats: health issues FDA label mandate cis form saturated trans form H H C C H C C H H C C Hydrogenation ; (Source: Wilson, 2004)
14
Plant Breeding Targets
3. Pest and Disease Resistance Soybean sudden death syndrome
15
Joint Germplasm Release (Drs. Arelli, Pantalone, Allen, Mengistu)
USDA-ARS and Tennessee Agricultural Exp. Stn. Release of JTN-5303 Soybean Resistant to multiple diseases: Soybean cyst nematode Sudden death syndrome Stem canker Frogeye leaf spot Charcoal rot
16
Plant Breeding Targets
4. Environmental Stress Tolerance
17
Plant Breeding Targets
5. Ease of Management Deployment of transgenic traits (e.g., transfer of herbicide resistant genes in commercial varieties)
18
Plant Breeding Targets 6. Adaptation to Mechanization
Source:
19
Plant Breeding Targets
7. Environmental sustainability Conservation Tillage Source:
20
Objective 3: know the basic principles of plant breeding
Importance of genetic variation and selection
21
What are the causes of biological variation observed in plants?
1. Genetic causes (mode of inheritance) single genes multiple genes 2. Environmental 3. GxE: the interaction between the genotype of the plant and the environment in which it grows
22
A plant breeder needs to:
be observant of phenotypic differences among plants understand the genetics have the imagination to visualize final product foresight to predict demand for future plant products
23
In plants, examples include:
Plant selections to improve plant traits are made by assessing plant phenotypes In plants, examples include: plant height plant and leaf morphology biomass yield seed yield chemical composition of plant tissues and seeds
24
Genetic variation: the basis for improvement
25
Phenotype vs. Genotype P = G + E + (GxE)
P is called the phenotypic value, i.e., the measurement associated with a particular individual G is genotypic value, the effect of the genotype (averaged across all environments) E is the effect of the environment (averaged across all genotypes)
26
If we could measure P in all possible environments and regard E as a deviation, then the mean of E would be zero and P = G. The genotype responds more strongly in some environments. Sets of environments tend to shift the trait value in one direction, other environments in a different direction.
27
Cultivar Breeding: A Recurrent procedure
Utilization of Germplasm Resources Release of New Improved Variety Development of Genetically Diverse Populations Vigorous Yield Testing
28
Controlled Cross Pollination
Parent 1 × Parent 2 Stigma
29
Objective 4: know some basic plant breeding methods and strategies
30
How do we breed improved crop cultivars?
1.Inheritance of trait
31
How complex is selection?
Qualitative traits, simple inheritance, controlled by major genes Quantitative traits, complex inheritance controlled be several gene loci
32
Qualitative traits Classified into discrete classes
Individuals in each class counted Some environmental influence on phenotype Controlled by a few (<3) major genes
33
Mendel’s seven traits showing simple inheritance
Figure 2.4 Source: Halfhill and Warwick, 2008, Chapter 3, in C.N. Stewart, Jr. (ed.), Available: Often single gene traits are easy to see or measure, since environment typically has limited control over their expression Tawny (TT or Tt) versus gray (tt) single gene locus on soybean chromosome 6
34
F1 Hybrid Plants: 100% yellow
Figure 2.5. A. Monohybrid Cross B. F1 Self Fertilization = Parent 1 Parent 2 Parent 1 Parent 2 X X YY yy Yy Yy Gametes: Y Y y y Gametes: Y y Y y F1 Fertilization: F2 Fertilization: YY Yy yy Y y Parent 1 Parent 2 Yy y Y Parent 1 Parent 2 YY & Yy Yy F1 Hybrid Plants: 100% yellow F2 Plants: 75% yellow 25% green yy Source: Halfhill and Warwick, 2008, Chapter 3, in C.N. Stewart, Jr. (ed.), Available:
35
Gene and Genotype Frequencies Example: Self pollinated diploid species
Upon selfing F2 population; 25% homozygous ‘YY’ will produce only ‘YY’ genotypes, and 25% homozygous ‘cc’ will produce only ‘yy’ genotypes. So only ‘Yy’ will segregate to produce genotypes in proportion of 0.25 (YY):0.50: (Yy):0.25(yy). F2 population: 0.25(YY ) 0.50 (Cc) 0.25 (cc ) YY Yy Yy yy 0.25 0.50 0.25 Produce all CC plants Segregate into 0.25(CC ) 0.50% (Cc) and 0.25 (cc) Produce all cc plants Resulting F3 population will have ½ (0.25) = CC plants ½ (0.50) = 0.25 Cc plants ½ (0.25) + (0.25) = cc plants
36
Heterozygosity reduced by half in each selfing generation
YY Yy yy F2 F3 F4 25% F5 F6 F7 50% 43.75% 46.88% 12.5% 48.44% 6.25% 49.22% 3.135 49.61% 1.56 F8 37.5% 0.78% When should we select?
37
Questions based on F5 single plant derived progeny rows from one population formed from crossing two pure line parents:
38
Selfing a double het (AaBb × AaBb) produces a 9:3:3:1 phenotypic ratio only if trait governed by complete dominance Freq Genotype 1/16 AABB 2/16 AABb AAbb AaBB 4/16 AaBb Aabb aaBB aaBb aabb Phenotypic Ratio Underlying Genotypes 9 AABB = AABb = AaBB = AaBb 3 AAbb = Aabb aaBB = aaBb 1 aabb Note: only 1 out of 16 is homozygous favorable allele for both gene loci
39
Selfing a double het (AaBb × AaBb) produces 9 genotypic classes
Freq Genotype No. of CAP alleles 1/16 AABB 4 2/16 AABb 3 AAbb 2 AaBB 4/16 AaBb Aabb 1 aaBB aaBb aabb Figure 3.1 Source: Tinker, 2008, Chapter 3, in C.N. Stewart, Jr. (ed.), Available: Freq No. of CAP alleles 1 4 6 2 3
40
Quantitative traits Express continuous variation (normal distribution)
Individuals measured, not counted Significant environmental influence on phenotype Controlled by many minor (or major) genes, each with small (or large) effects
41
X aa, BB (6 kg) AA, bb (6 kg) Aa, Bb (6 kg)
Note: Consider upper case letter represents the favorable allele for each gene Self-pollinate 4 kg: aa, bb 5 kg: Aa, bb (x2) aa, Bb (x2) 6 kg: Aa, Bb (x4) AA, bb aa, BB 7 kg: Aa, BB (x2) AA, Bb (x2) 8 kg: AA, BB Histogram depicts dominant genotype effect with yield: “capital” alleles (0, 1, 2, 3, 4) Figure 3.1 Source: Tinker, 2008, Chapter 3, in C.N. Stewart, Jr. (ed.), Available:
42
High yielding low-phytate parental lines is the goal
Frequency distribution of seed yield for 187 different recombinant inbred lines (RIL) in the soybean population 5601T x Cx (Scaboo et al., 2009) [no transgressive segregates for this trait in this population] 5601T = 3252 Cx High yielding low-phytate parental lines is the goal
43
15/16 7/8 3/4 1/2 (15/16)20 (7/8)20 (3/4)20 (1/2)20 = [1-(½)G]L
Adapted from Allard, 1999 Then find the better individuals among the homozygous plants (those accumulating the greatest number of superior alleles). Can be done with DNA technologies and progeny row testing. 15/16 7/8 3/4 1/2 (15/16)20 (7/8)20 (3/4)20 (1/2)20 Even if 20 genes is involved, using the power of inbreeding 5 generations, over half the proportion of individuals will be completely homozygous!
44
How do we breed improved crop cultivars?
2. Understand the effect of reproductive behavior
45
Reproductive Behavior
Self pollinated Pure line variety Hybrid variety Monoecy Cross pollinated Dioecy Self-incompatible - Synthetic variety – heterogeneous population (not a pure line) - Hybrid variety, if inbred development is possible Perfect flower Clonal variety Hybrid No flowering/limited flowering Vegetative reproduction
46
Cultivar development for self-pollinated species: pedigree method
Cultivar, local or exotic landraces, wild relatives Germplasm Hybridization Parents are usually inbred F1 Nursery, all plants heterozygous Homogeneous population if parents were inbred F2 Nursery, all plants heterozygous Every single plant is a different genotype F3: head rows Select the best rows, select best plant within selected rows, proceed to F4 head rows This is typical pedigree method of selection in self-pollinated crop. Each head row is called line. Most F6 or F7 lines are uniform enough for preliminary yield testing
47
Cultivar development for self-pollinated species: bulk method
Cultivar, local or exotic landraces, wild relatives Germplasm Hybridization Parents are usually inbred F1 Nursery, all plants heterozygous Homogeneous population if parents were inbred F2 population, all plants heterozygous Collect equal amount of seed from each plant F3: bulk population Repeat one or two more generation, then follow head rows This is bulk method of breeding self-pollinated crop. Most F6 or F7 lines are uniform enough for preliminary yield testing. This is less resource consuming.
48
Cultivar development for cross-pollinated species: recurrent phenotypic selection
Starting population cycle 0 (C0) Select best plants (phenotypes) Produce cycle-1 (C1) seeds Polycross selected plants Repeat cycle Space-plant C1 population, select the best plant (with respect to target trait) Eliminate unselected, intercross selected & harvest seed & bulk Harvest seeds from selected plants & bulk Field testing of seed in each cycle
49
Field testing of new synthetics: evaluation
Cultivar development for cross-pollinated species: recurrent phenotypic selection, continued Phenotypic selection Progeny evaluation - Genotypic selection among families - Selection among-and-within families Repeat cycle Select superior genotypes of superior families Select parents producing superior families Intermate selected genotypes Synthetic seed production Field testing of new synthetics: evaluation Multilocation yield test
50
How cultivar development can be accelerated
One method: backcross breeding
51
BC1F1 75 % TN Line BC2F1 87.5 % TN Line BC3F1 93.5 % TN Line
With Traditional Backcross Breeding: 2000 F1 50 % TN Line BC1F1 75 % TN Line BC2F % TN Line BC3F % TN Line BC4F % TN Line BC5F % TN Line BC6F % TN Line With traditional backcrossing you increase the amount of your recurrent parent each generation and it takes 6 generations to recover 99% of your chosen parent. With the use of molecular markers we have already been able to speed up this process. Notice that these calculated values show that the BC1F1 should contain on average 75% of the desired line. A BC1F1 is produced by using the Recurrent line 5601T as the female and using the F1 as the donor or pollen source. A BC2F1 is produced by using the Recurrent line 5601T as the female and using the BC1F1 as the donor or pollen source. 2006 – just a few pods produced
52
Molecular markers allow visualization of genotypes
RR RR RR rr rr rr rr Rr Gel electrophoresis of DNA markers: we can now ‘see’ genotypes
53
2003 winter plant-row increase 2004 TN yield tests & re-selections:
Molecular genetic markers can accelerate breeding with fewer generations needed F1 50 % TN Line BC1F % TN Line BC2F % TN Line BC3F % TN Line 2003 winter plant-row increase 2004 TN yield tests & re-selections: 2005 harvest 100+ bushels 5601T-RR With traditional backcrossing you increase the amount of your recurrent parent each generation and it takes 6 generations to recover 99% of your chosen parent. With the use of molecular markers we have already been able to speed up this process. Notice that these calculated values show that the BC1F1 should contain on average 75% of the desired line. A BC1F1 is produced by using the Recurrent line 5601T as the female and using the F1 as the donor or pollen source. A BC2F1 is produced by using the Recurrent line 5601T as the female and using the BC1F1 as the donor or pollen source. 2002
54
Phytate quantitative trait loci (Walker et al. 2006) now with
confirmed quantitative trail locus (QTL) designations (Scaboo et al., 2009) ♦ Satt156 Satt527 Satt561 Satt229 Satt373gs Satt530 Satt387 Satt339 Satt237 GMABAB Sat_091 Sat_236 10 cM LG L LG N Maximum LOD: 6.4 R 2 : 13% LOD : 25.5 : 40% Pha-002 Pha-001
55
2008 phytate yield trial 33 new BC lines
Less agronomic QTL for HT QTL for MAT a BU/A a b 55
56
Biotechnology can be used to improve crop cultivars?
3. Transgenic varieties
57
Source: http://en.wikipedia.org/wiki/Gm_crops
58
TN soybean producers of
IMPACT For every 1 bushel/acre increase in production, largely through genetic gain, increased income to TN soybean producers of 15 Million $ annually 5601T UT AgResearch soybean at Obion, TN
59
USG Allen #1 and better than average in every county
Yields of 18 Maturity Group V Roundup Ready soybean varieties in 9 County Standard Tests in TN and KY during 2007. MS Brand/Variety AvgYld Moist Carl Dyer Gibs 1 Gibs 2 Hayw Laud MREC Obio Weak bu/a % planted 5/26 5/21 6/18 5/14 5/17 5/22 5/15 6/7 5/23 A *USG Allen 41.3 16.0 63.1 53.0 37.0 41.1 32.2 29.7 33.5 35.6 46.1 AB Delta King DK52K6 40.0 15.3 62.4 49.7 40.1 30.1 30.7 35.7 27.2 36.4 47.4 ***Delta King DK5567 39.9 67.4 50.5 34.1 37.8 34.5 33.6 27.4 34.2 ABC **Armor 54-03 39.2 13.9 61.6 52.5 31.0 25.7 28.1 34.6 27.1 30.8 61.8 Ag Genetics South AGS 568 38.2 15.8 56.5 41.0 44.3 34.7 33.9 35.0 28.5 35.2 34.9 Dyna-Gro 33X55 38.0 15.6 56.7 51.6 33.2 26.4 31.5 26.5 37.6 44.8 BCD **Dyna-Gro 33B52 13.3 46.0 36.5 22.8 28.4 27.8 42.1 CD Pioneer 95M30 35.4 15.1 51.4 47.2 31.1 23.2 31.7 29.8 19.2 53.3 Schillinger 557RC 35.3 15.2 56.9 54.1 17.3 21.5 30.0 23.9 31.9 DE Stine RR/STS 33.3 15.4 47.8 39.1 22.3 20.4 28.7 24.4 31.3 EF Vigoro V51N7RS 30.3 14.3 45.3 42.7 16.9 20.8 29.5 24.6 32.4 EFG FFR 5116 30.2 14.1 46.5 18.2 29.2 20.6 34.3 27.3 Armor 52-U2 29.9 14.0 50.9 44.2 18.8 16.4 29.4 18.4 Dairyland 8512 14.6 44.5 19.0 19.3 19.5 38.5 FG Progeny 5115 13.5 50.6 14.5 22.6 15.7 28.3 Deltapine DP5115 RR/S 26.8 48.2 27.5 15.0 17.9 25.9 18.3 Delta King DK5066 53.6 10.1 12.1 33.4 G Dairyland 8509 25.8 13.6 54.0 21.8 16.1 14.9 26.0 Average (bu/a) 54.5 42.8 34.0 23.7 23.8 32.1 38.6 +7.8 +8.6 +10.2 +17.4 +8.4 +10.7 +7.5
60
For the plant breeder patience is a virtue
…when working with new genetics
61
Key points Know basic terminology in transmission genetics and plant breeding Understand the goals of plant breeding Know plant reproductive syndromes, e.g., self-fertilization, and how they effect breeding methods
Similar presentations
© 2025 SlidePlayer.com Inc.
All rights reserved.