Plant landraces, varieties and breeding

Question 1

The next steps

Answer 1

landrances

‘scientific selection’ leading to varieties

Biotechnology

Question 2

Landraces

Answer 2

Traditional, locally adapted, visuayl and genetically distinct varieties of crops that have been developed and maintained by farmers over generations through selection and adaptation to specific environmental conditions.

Key features:
- Genetically dynamic over time – yearly changes in selection pressures have effect
- More homogenous than wild, but less homogenous than modern varieties
- Are source of genetic variability to improve modern crops ( loss / erosion of landraces threatens genetic variability)
o High yield stability – little yield variation between years
o But low yield compared to modern crops

Example: Rice has over 100,000 landraces
- Jarneli, Kalo marshi, Kalo nuniya
- nutritious, medicinal, abiotic stress tolerance and resilience to low fertility soil

Question 3

Varieties

Answer 3

Started appearing in early 19th century via conscious human selection leading to bottlenecks for diversity

Key features:
- more homogeneous than landrace
- standardisation / uniformity (so all flower + are harvested at same time)
- Landraces became varieties via scientific breeding

Example: squareheads master (19th century wheat) for thatching (poor grain for bread, robust straw)

Question 4

The rise of ‘scientific breeding’ breeding

Answer 4

The rediscovery of Mendel’s law and the developement of ideas about mechanism of inheritance (chromosomes and linkage) lead to rise in plant breeding with aim to harness genetic diversity and select for plants with improved characeristics

Simple breeding:
i. cross pollination of 2 selected indivs (and selfing prevented)
ii. Pollinated plants bagged to prevent fertilisation by pollen of other males
iii. Seed collected + sown -> uniform F1
iv. F1 self-pollinated -> diverse F2 pop’n

Pedigree breeding:
- sow best F2 over and over again

Hybrid breeding
- Select hybrids from F1 with hybrid vigor / heterosis (larger and more productive)

Mass selection used in past:
- a large number of seeds with similar/ desirable phenotypes are selected and grown
- Not scientific plant breeding - purely from looks

Question 5

How to increase the pase of breeding with new techniques

Answer 5

1. Parallel selection programmes – grow in northern then southern hemisphere (allows 2 generations per year)
2. Double haploids – make desirable haploid plants then make them diploid using colchicine (100% homozygous in one generation rather than many)
3. Embryo rescue – expands range of available characters as crosses that normally make non-viable offspring are made viable
   -> Hybrid embryo won’t normally develop further – so cut out + culture aseptically and it grows
   -> Eg. for increased salt tolerance as wild species often more salt tolerant (cross wild w/ modern variety often unviable)

The rise of the genomic science -> transforms understanding of function and lcoation of genes.

5. Marker assisted selection where a trait of interest is selected based on a marker linked to a trait of interest (commonly used to select plants most similair to parents for backcrossing)
6. Transformation GM – add / modify / delete traits w/out shuffling entire genome by crossing
7. Genome editing – CRISPR/cas9 - More precise deletion, insertion of DNA

Question 6

Using a model organisms to inform breeding in a crop: Oil Seed rape

Answer 6

Aims:
- speed up domestication
- improve shattering (20% lost each year)

Model: Arabidposis (small plant, short generation time, easy to cross)

Method 1: Overexpression of FUL by 35S:FUL to supress IND (valve margain)
- Pods are completely seeled so farmers would have to open every pod

Method 2: EMS creating variety of IND mutants
- Variety selected with reduced IND activity where intermediate valve margain remains

Method 3: Mutating GA4 using CRISPR/Cas9 to defect valve margin developement
- This both reduces replum and makes the mutants smaller
- Design RNAse that only targets one copy of the gene

Returning to OLS:
- 2 genome copies (A and C) - want mutation in one of the copies.
- Test for best mutant: random impact test where pods inside tupawear are shaken for 8s, intact pods calculated and halflide recorded.

Question 7

Legislations

Answer 7

GM are banned in Europe

2018: European court of justice decided that gene editing should be equated with GMO even though the processes are very different.

2019: the first Defra-approved Field trial was varried out

2023: In Britain, gene editing was ruled different to GMO

Question 8

Overview

Answer 8

1) land races
2) Varieties

Plant breeding
- Generic breeding
- Hybrid breeding
- Pedigree breeding

Imporving the rate of breeding
- parallell selection
- haploid
- embryo rescue

The rise genetics further improving breeding
- Marker assisted selection
- Gene editing
- Gene modification

Understanding gene editing in model organisms which are easier to manipulate can be applied to crops.