Transcript Principles of classical breeding

The base line of plant breeding
Zoltán Bedő
EUROPEAN ASSOCIATION FOR RESEARCH ON PLANT BREEDING
EUROPÄISCHE GESELLSCHAFT FÜR ZÜCHTUNGSFORSCHUNG
ASSOCIATION EUROPÉENNE POUR L'AMÉLIORATION DES PLANTES
Main trends of plant breeding in the 20th century
R. W. Allard (1996)
Cultivated crops
Level of
population
heterogeneity
Landraces
high
Old variety populations
high
Selected old varieties
medium
Modern varieties
homogen
As a result of the selection by breeders a genetic
erosion occured by the disappearance of old
landraces and varieties having high level of
heterogeneity in their populations
Continuous efforts during several breeding cycles
have led to the accumulation and preservation of
favourable alleles for a better adaptation and
agronomic performance in modern varieties
Breeding progress
• Discovery and generation of genetic variation
• Accurate selection genotypes with new traits
• Transgressive segregation is the source for continued progress
Principles of classical breeding
• Biology of sexual reproduction
• Knowledge of trait heritability
• Mode of inheritance
• Number of genes controlling
inheritance
Classical variety breeding
Determination of the ideotype, breeding
objective
Assesment of genetic variation, genetic
resources
Crossing + Evaluation + Selection
Screening, data management
Release of new variety
Maintenance breeding – stability of traits
(UPOV regulations)
• Vegetatively propagated crops
(bulbs, tubers or cuttings, etc.
• Self fertilzers crops like wheat,
soybean, leading to variety
selection
• Heterosis breeding to develop
hybrids by crossing inbred lines
Modern crop varieties selected by classical breeding
•
•
wide adaptability across different environments instead of locally adapted crop
populations
high level of yield potential and high interplant competition ability
Changing plant architecture
Harvest index – ratio of vegetative/generative parts
34% old 40% new varieties
32% old 38% new varieties
22.9% old 47% new varieties
21.2% old 43.5% new varieties
optimal ratio 50%
Leaf size
Flag leaf area
Flag leaf senescence
Rate and duration of grain filling period
Assimilate translocation to the grain, etc.
250000
3
200000
2,5
2
150000
1,5
100000
1
50000
0,5
Area (1000 ha)
Average yield (t/ha)
1996-2000
1991-1995
1986-1990
1981-1985
1976-1980
1971-1975
1966-1970
1961-1965
1956-1960
1951-1955
1946-1950
1941-1945
1936-1940
1931-1935
1926-1930
1921-1925
1916-1920
1911-1915
1906-1910
0
1901-1905
0
Year
Average yield (t/ha)
Wheat production in the XXth century
Area (1000 ha)
Van Dobben (1962)
Vogel et al. (1963)
Szunics et al. (1985)
Litvinenko (2001)
Lukjanenko (1966)
Genetic improvement in yield-related
traits in cereals (Evans et al. 1981)
Genetic resources to increase genetic variation
Genetic resources
Genetic variation
elite varieties
exotic germplasm
old landraces and variety populations
wild and cultivated relatives
mutant genotypes
X
XX
XXX
XXXX
XXXX
Elite x elite crosses - differences between alleles in new commercial varieties are diminishing
potential increase of genetic vulnerability
Wild and cultivated relatives sources of new disease resistance genes
drought tolerance,
nutritional quality traits, etc.
best sources to widen genetic variation
Disadvantages of the classical use
of wild and cultivated crop relatives
• crossability
• genetic linkage to unfavorable traits
• low yield potential
• low efficiency of breeding
Most successful introduction of a foreign chromosome segment
from a cultivated relative into wheat with classical breeding method
The wheat × rye translocation story
The first wheat × rye crosses were made by Riebesel with Petkus rye in 1924
The Criewener 104/Petkus rye hybrid combination resulted in the line Riebesel 47-51
The first commercial cultivars were released in Germany in 1957 (Halle 14-44, ST 14-44 and
Neuzucht 14-44) : Pm 8, Lr 26, Sr 31, Yr 9, etc.
Broad dissemination in 1980-90: many tens of millions of hectares/year worldwide
Regardless the introduction of foreign genes there were no food safety problems reported
until now
Disadavantages of the introduction with classical breeding methods
very long breeding period (33 years)
close linkage with unfavorable traits – poor breadmaking quality
sticky dough
Looking for new methods to improve efficiency
Development of tissue culturing
Doubled haploid breeding
Induction of somaclonal variation
Origin of the gene in traditional plant breeding with history
of safe use
(Jacobsen, 2009)
Domestication of crops with selected alleles
Genetic variation in natural populations within crop species or in
crossable species;
Natural and induced mutations of existing alleles
Synthesis of new crops like Triticale, Hordecale and resynthesis of
existing allopolyploid crops
Domestication of individual traits by introgression and translocation
with linkage drag
Breeders gene pool is within species or crossable wild species
(including bridge crosses; embryo rescue, etc.) leading to varieties
as sources of safe food production
Results achieved by classical breeding
Cereal example: production and area saved by improved yield
(Borlaugh and Dowswell 2005)
1800
World cereal production
620 million tons
1,874 million tons
1600
1400
Million hectar
1949-51
1999
1200
1000
800
600
400
200
0
1950
1960
1970
area in 1999
Biomass (g/m2)
1980
1990
1999
area on the yield level in 1949
Genetic gain of yield due to the breeding efforts
Straw (g/m2)
Grain (g/m2)
0
200
400
600
800
Very old
Old
Intermediate
1000 1200 1400 1600
Modern
England
1908-1985
France
1950-1999
Hungary
1960-1985
Mexico
1950-1982
Kansas USA 1919-1987
38 kg/ha/year (Austin 1989)
50 kg/ha/year (Bonjean 2001)
59 kg/ha/year (Balla et al. 1986)
60 kg/ha/year (Hernandez Sierra 1988)
16 kg/ha/year (Cox et al. 1988)
Plant breeding faces new challenges
Annual average increase in world wheat production in the 2nd half of the
20th century (L. R. Brown 1998)
3,5
The yield increase slowed
down – main constraints of the
yield improvement:
3
2,5
2
1,5
1
0,5
0
1950-60
1960-70
1970-80
1980-90
1990-95
• yield stability
• higher quality requirements
• chemical input limits
• climate change effects
• food safety concerns
Risk of safe food production - will the pathogens always win?
•
•
•
•
Wind and modern transport systems disperse new, aggressive pathogens world-wide
Recombination generates new genotypes
New pathogen effector genes evolve to overcome new host resistance genes
Pathogens adapt faster to a changing climate than crops can
Barriers of classical breeding
It is impossible to combine all the best alleles at all loci that are segregating for a
quantitative trait into a single genotype and to identify that genotype (Sorrels et al. 1997)
Classical plant breeding and biotechnology in Europe
(Forecast by: Arundel et al. Nature Biotechnology 2000)
1
Genetic engineering and classical breeding 49% (???)
Assisted classical breeding involving marker technologies and
sequencing 31%
Only classical breeding 20%
Improvement of conscious selection - marker technologies
Genome projects in plant breeding - availability of sequence data
(public databases)
Transfer of data from fundamental research to plant breeding
Development of user- friendly markers for molecular marker
assisted selection (MAS)
Implementation of molecular markers in classical breeding
Introduction of new technologies in agriculture?
Tremendous development in life sciences like health care, food
industry, environmental sector
Focused narrowly on gmo crop breeding can cause delay in the
application of other new rapidly emerging technologies in
agriculture
2
3
4
Baseline of plant breeding and its future
perspectives
Continuous efforts have led to the accumulation and preservation
of favourable alleles for a better adaptation and agronomic
performance of cultivated crops
The results achieved in classical breeding during the period from
the discovery of Mendel’s Laws to the present form one of
mankind’s success stories
Further improvement will be necessary taking into consideration
new challenges in food security and safety for the well being of
the society
Integration of novel technologies into classical breeding is
necessary to identify and use of new genetic variation for the
future progress
Maybe cisgenesis is one of the new technologies to help classical
plant breeding?
Thank you for your attention