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Summary Course 9 Plant Biology term 2 £4.01
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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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  • Chapter 7, 10, 11, 12, 13, 14, 22
  • January 14, 2022
  • 57
  • 2021/2022
  • Summary
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Plant biology course 9 term II
Lecture 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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