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Summary Course 9 Plant Biology term 2
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Summary of the Biology theoretical lessons in term 2 of course 9. Books iGenetics and Plant Biology are used for additions.
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Plant biology course 9 term IILecture 1 classical & modern breeding
Main breeding goals
- Increased biomass accumulation
- Increased harvestable yield
- High nutritional quality
- Resistance to pests
• Not allowed to use all chemicals → environment
- Performance in high stress environments
- Plant architecture
- Photoperiod response
• Plant producing tubers or flowering
- Processing characteristics
• Starch quality in potato
- Dormancy suppression
• Cold treatment induces flowering → reducing time period for more yield
Basic steps in plant breeding
1. Creation of variation
2. Selection
• Can take long time
3. Evaluation
4. Release
• Private producer/ firm for further commercial testing
• Quality criteria = DUS (distinctness, uniformity and stability)
5. Multiplication
6. Distribution of the new variety (formal release)
1 to 10.000 species to come to evaluation will pass next steps
Creation of variation
1
,Finding variation
- Centers of origin of crop
• Lot of variation in one crop
• 8 major centers
Polyploid crops
- More sets of chromosomes than 2 → polyploid
- Plants have bigger cells, bigger organs so bigger plants
• Also bigger fruits so favourable
- Polyploid crops can be sterile (useful in seedless fruits like banana)
2
,Allopolyploidy vs autopolyploidy
- Allopolyploidy
• Mating of 2 different species
- Autopolyploidy
• n chromosome sets from the same species
Hybrid vigour/ heterosis
- 1908: Shull, plant breeder, reported results of crossing maize plants from 2 different inbred
lines
• Inbred lines: 20 bushels of maize per acre, outbred offspring produced about 80!
• This strength in the heterozygous outcross is called hybrid vigour
- Heterosis is the superior performance of hybrid organisms compared with either of their
parents
• In colour, in mass, in flavour etc.
Genetic basis of heterosis
- Suppose that the gene combination AaBb is desirable for a hybrid F1
• Can be achieved by crossing 2 inbred lines: aaBB x AAbb
- AaBb is sold to farmers
- Which percentage of F1xF1 offspring has the desirable gene combination?
3
, - Bad news for farmers, but good news for seed supplying companies!
Hybridization
- Self-incompatibility
• Many angiosperms have mechanisms that make it difficult/ impossible for a flower to
self-fertilize
▪ Unisexual flowers → dioescious species
▪ Containing stamens and carpels that mature at a different time
Pollination systems for crops
- Self-pollinating crop
• Primarily homozygous
• Initial hybridization can be difficult
• Varieties: pure line/ inbred line → 1 genotype
- Cross-pollinating crop
• Heterozygous
• Hybridization: difficult to prevent unwanted pollen from fertilizing the parent
• Varieties: hybrid or populations (mixtures of heterozygous plants)
Self-pollination consequences
- Self-fertilization can lead to inbreeding depression (= antithesis of hybrid vigour)
• Reduction or loss in vigour and fertility as a result of inbreeding (e.g. self-fertilization)
- Many plant species can prevent self-fertilization:
• Pollen separated from stigmas in space or time
• Self-incompatibility (SI)
4
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