Convention plant breeding
Producing a new variety of cultivar
varietal development
1. Producing or identifying genetically variable germplasm
germplasm
genetic material that carries the inherited characteristics of an organism
2. Carrying out selection procedures on genotypes from within this germplasm to identify superior genotypes with specified characteristics
3. Stabilising and multiplying these superior genotypes to release cultivars for commercial production
DUS test
Distinct - different from any others already in existence
Uniform - the level and type of variation that exists between plants within a cultivar
Stable - the cultivar remains true to its description when it is reproduced or propagated
Cultivars often then go through VCU tests
Value for Cultivation and Use
History of conventional Plant breeding
Began with domestication around 9000 years ago
modern plant breeding started around the turn of the century
Darwin + Mendel
the work of Weissman + Johannsen resulted in the idea of genetype/phenotype relationships
World Population
1922 - 2 billion
1955 - 3 billion
1974 - 4 billion
1987 - 5 billion
1999 - 6 billion
2012 - 7 billion
2028 - 8 billion (estimated)
Food production increases (1955 - 2005)
Cerials - 123%
Roots - 36%
Pulses - 40%
Oil crops - 130%
Veg - 80%
Fruit - 42%
What has happened as a result of conventional plant breeding
Increased yield as a result of
Increased growth rate
increased ability to grow in higher densities
increased vigour or to resist wear
change in harvest index
desired proportion of growth
e.g. tomatoes on a tomato plant
Increased end user quality as a result of
Breeding for
texture
colour
taste
size
chemical quality of the product
mainly food or oil crops
Increased resistance to pests and diseases
Comparison of two breeding systems
Inbreeding
selection process
single parent section
if possible
continue self-fertilisation to reveal dominant + recessive alleles
after 6-7 generations, population almost entirely homozygous
characteristics are said to be fixed, others are selected out
this selection process leads to great variation between lines
heterozygosity can be introduced by
accidental hybridization
mutation
inbreeding program
taking a large number of superior plants
raising self progenies for each of these
i.e. self pollinating the selected superior plants and raising these
selecting superior lines each year from these progeny
replicating trails over several seasons to compare lines with each other ( and existing commercial varieties)
Outbreeding program
there is a constant recombination of alleles
pieces of DNA are broken and recombined to produce new combinations of alleles
creates genetic diversity
results in individuals with a high degree of heterogeneity
if the population is subject to self fertilisation, inbreeding drepression can result in
Loss of vigour
loss of fertility
loss of productivity
possible for some lines to become extinct
recessive homozygous plants often have deleterious effects when revealed in the phenotype
plants are largely heterozygous
the recessive allele is hidden and not expressed
inbreeding can cause the recessive allele to become expressed
modified form of inbreeding
only allowed to inbreed for a few generations
inbred lines are then inter-crossed to regenerate heterozygosity
plants with desired characteristics from this cross are selected
some species have a high degree of self-incompatibility
cannot be self fertilised