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· Basic raw material of any plant breeding program.
· A collection of genetic resources.
· the source of genes used to create genetic variability
· geographical area in which the crop had originated and frequently where it evolved or was domesticated
· Greatest concentrations of genetic diversity could be found.
· They were primarily near the equator and therefore, were unscathed by glaciers.
· They were also primarily in developing countries
primitive domesticates that evolved on farmers’ fields.
· evolution resulted from farmers growing and replanting their own seed
· Faced with natural selection and whatever selection individual farmers placed on them.
· Evolved to be as productive as possible in the characteristics of the environment they’re in
· Multiplying, evaluating and maintaining the collection
· Distributing the seed of plant accessionsDetermining the needs and assisting with foreign exploration
Various types of germplasm collections including active collection, backup collections and working or breeders collections
Active collection- at the regional stations, available upon request, periodically re-grown to ensure sufficient seed is available for distribution
Backup collections- supplement the base selections, available in case of a disaster at the location of the base collection
Working or breeders collections-elite lines and adapted germplasm within breeding programs, unique alleles for introgression should they be needed
Genetic homogeneity and uniformity of a group of plants predisposes it to susceptibility to a pest, pathogen or environmental hazard.
Texas male sterile cytoplasm in corn, linked to susceptibility to southern corn leaf blight
move traits from less adapted germplasm into adapted germplasm. INTROGRESS. Creates parents that can be used in breeding, not used as cultivars directly. Separate program, benefit is more diversity while reducing impact on progress of using unadapted germplasm directly.
seed of all selections are bulked together to form a new variety, increase desirable alleles and reduce the undesirable alleles in a heterogeneous population
Does NOT include yield trials or result in pure lines
new variety is derived from progeny of a single pure line, upon release the variety is practically homozygous and reproduces itself as such
most widely used of basic pure line breeding methods
Develop varieties in self-pollinated crops
Advancement from one generation to the next is by single plant selections followed by progeny testing
Selections are always kept separate in progeny tests-lead to pure lines
· rapidly inbreed a segregating population in which no early generation selection was required (e.g. for elite x elite lines.
· Selection then on quantitative traits (low H) after homozygous line have derived.
· If you only advance 1 seed/plant/generation, you can do it in the greenhouse to reduce time to reach homozygosity.
· For a crop with a spring growth habit, you could grow 2 generations in the greenhouse (1 in the fall; 1 in the spring) and then take the 3rd generation to the field in the summer.This would shorten the time frame from the parental cross to F6 seed to 2 years
1. Inbred, pure-line populations.- homogeneous,-zygous, selections from transgressive segregates of crossed inbred lines
2. Open-pollinated populations.- heterogenous,-zygous, change gene frequencies by selection
3. Hybrids, constructed by crossing inbred lines.- homogeneous, heterozygous, cross inbred lines
4. Clones (non-seed propagated populations- homogeneous
In general, the breeding scheme for self-pollinated crops involves 5 steps. What are they? What is the end result of these steps?
1. parental selection
2. variation through hybridization and recombination
3. select from segregating populations with desirable agronomic traits
4. advance through f2-f5, yield testing f6-f10 good lines retained
5. increase and release of superior lines
You won’t be able to understand/ do the crosses if you don’t know what part is what and its function
To create variability. If you don’t have the traits you need in the parents, you won’t have them in your progeny
Describe in general the genetic changes you would expect in a self-pollinated populationas you advance from the F1 through to the F12
· without selection.
F1 is highly heterozygous, self-pollinating itself over and over results in filial generations with decreasing heterozygosity and increasing homozygosity, dominant and recessive
· With selection
F2 Maximum genetic variation; High heterozygosity
F3 – F6 Declining heterozygosity; Lines assume individuality
F5 – F8Surviving lines are effectively homozygous; Genetic variability greatly reduced
F7 – F12 Very few genotypes survive; Genotypes are essentially pure-lines (homozygous
Criteria for Parental Selection for ‘Yield Breeding’
1. Yield of the parents
2. Breeding record
3. Pedigree of the potential parent
4. Select parents based on phenotypic traits that contribute to increased yield
List in order of priority and briefly describe the five general sources of parental material
1. Commercial cultivars- most commonly used because they are the most elite germplasm. Fewer desirable genes because they’ve been intensely selected. Provide greater chance of progress
2. Elite breeding lines- advanced stages of testing, should be superior to cultivars because we keep lines that are better than the best cultivars
3. Acceptable breeding lines with superiority in one trait- may not have overall performance but superior in one trait
4. Plant introductions of cultivated species- from outside your area, have many unacceptable traits because of poor adaption, may have 1 or few desirable traits
5. Related Species- used for specific traits, only if trait cant be found in adapted germplasm
Who was Nicolay Vavilov and what two major contributions did he make to the field of plant breeding?
· Russian scientist who wanted to increase ag production and provide humankind with more food.
· He was among the first to make plant collections in an effort to preserve the diversity of these species
· there were large reservoirs of genetic diversity. = ‘Centers of Origin’ of cultivated plants. .
What role did plant introduction play in the development of semi-dwarf cereals?
Semi-dwarf wheat and the intercontinental germplasm exchange of reduced height genes:
Japanese introduced two North American wheat varieties, inserted 2 reduced height genes, Norin 10 was produced and reintroduced to the US and was used in the green revolution.
What are 3 problems associated with the use of plant introductions in plant breeding programs?
1. problems with adaptation and determining how these will do in a new environment is difficult
2. Large numbers of introductions available for all crops – so how do you decide which to use.
3. difficult to determine prior to use, the potential of a given introduction as a parent
4. person evaluating is a botanist or taxonomist who is not necessarily familiar with the needs of breeders, growers, or consumers
The PI was male because the line was unadapted, therefore we won’t want cytoplasmic (female) genes from it
Contrast Mass Selection with Pure-line Selection
· Mass Selection- seed of ALL selections are Bulked to form a new variety, increase desirable alleles in a heterogeneous population
· Pure-line- new variety is derived from progeny of a single pure line or a single plant selectionUpon release, the variety is practically homozygous
List and briefly (in a sentence) describe 3 uses of plant introductions in plant breeding programs?
1. Directly as cultivars- without plant introductions we wouldn’t be growing a lot of our crops
Are generally the best varieties where it comes from, performance is tested extensively before making it available
2. Parents in breeding programs- for source of abiotic or biotic stress resistance
3. Used for selection- are heterogeneous (of an outcrossing crop) as a base population
4. Genetic conservation- save genetic diversity
1. The heritability of the trait(s) under selection:Progress is better for traits with high heritability2. The breeder’s ability to see clear phenotypic differences among the plants for the trait being selected for.E.g. If you infect the population with disease, mass selection for disease resistance will be more effective because the genotypic differences within the population will be expressed
Give two advantages of using mass selection in a self-pollinated crop.
1. rapid and inexpensive procedure for increasing the frequency of desirable (alleles) within a segregating population.
2. No yield trials are generally required so a population can be quickly released
1. Only In environs where the trait can be expressed
2. Effectiveness is determined by heritability because selection is based on individual traits and is only assessed in one environ
3. Limited value for traits with low heritability
4. Does not lead to pure lines
In thinking of all pure-line breeding methods you can break down an entire breeding cycle (i.e. from parental choice to variety release) into three stages. What are those three stages?
1. Create variation
2. reduce heterozygosity in segregating populations
3. yield trials and Release of homozygous pure line
Deriving lines is common to all pure-line breeding methods. What is an F4:5 line and how mechanically does it differ from an F4:6 line?
Generation of selection: Generation line is currently in.
An F4:5 was a line selected in the F4 and is currently in the f5. An F4:6 is also derived (selected) from the F4 but is now in the F6
Considering the pedigree method, when would you select for the following: (i) traits with high heritability; (ii) traits with low heritability. Explain your answer for each.
1. Heritability- progress is greater for characters with high heritiability, the phenotype approximates with the genotype, and therefore progress is expected to be high. Even for traits that aren’t visual but can be determined by tests.
2. Number of characters under selection at one time- as the # of characters increases, so does the total number of genes under selection, your ability to find desirable combinations decreases and progress is slower, so you must increase the number of lines grown to up your chances of finding lines with all traits, especially if one or more parental lines is unadapted.
3. Environs in which selection is done- genes need to be expressed in the phenotype, you need environs where genetic differences are expressed
1. If selections are effective, inferior genotypes will be discarded before inbreds are evaluated in expensive yield trials
2. Each generation is grown in a different year: exposed to a different environ, opportunity for genetic variability to be expressed, increases selection efficiencyWe know the genetic relationship of all our lines b/c of the extensive record keeping, maximize genetic diversity among lines kept
Give and briefly explain 2 advantages and 2 disadvantages of the pedigree method.
1. You must have environ that will maximize gene expression for the various traits
You CANNOT advance in greenhouses or winter nurseries, more time
2. Record keeping is excessive
3. Need experience to make selections4. Labor, land and money intensive
Contrast the pedigree and bulk breeding methods as you advance generations from the F2 through to the F5.
List four factors that will influence the frequency of genotypes as you inbreed a population using the bulk breeding method.
1. Genetic potential of a genotype to yield- plants that yield well will be used more often in filial generations
2. Competative ability of the genotype- more competitive the more seeds will be in final bulk
3. Influence of te environ on the genotype, it will be productive if the genotype does well in the environ
4. Randomness of the sub sample- If you can only have so much seed, you have to pick as much as you can take- RANDOM
Bulk breeding can be very effective in shifting gene frequencies for traits that are highly heritable if you combine it with some type of mass selection. Explain.
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