Plant Breeding Lecture 13.

 

Develop/release cultivars self-pollinated crops

  1. Introductions
    1. from another programs
    2. buy sister line
    3. brokers that buy germplasm

 

  1. Selection from cultivar/landraces
  2. Mutation breeding with elite lines/cultivars (earliness, short stature)
  3. Hybridization/selection
  4. Somaclonal variation
  5. Biotechnology – backcross

 

Discuss examples from Crop Science on new cultivar releases

 

Cross-pollination Crops

  1. Heterozygosity –cross-pollinated
    1. Monoecy; Dioecy; Protandry; Protogynous; Self-incompatibility

 

  1. Hardy-Weinberg law of Genetic Equilibrium – genotype and phenotype frequencies are maintained after one round of random mating.  Assumptions:
    1. Random mating
    2. No directional selection
    3. Equal mutation rates  A1→←A2
    4. No immigration or emigration of alleles
    5. Large number of individuals
    6. Diploid composition

 

  1. Heterozygosity – cross-pollinated
    1. General combining ability – cross with broad base heterogeneous collection of pollen of known origin (Top cross)
    2. Specific combining ability – cross with narrow genetic base (Test cross)
    3. Genetic variance – additive – dominance – epistatic
    4. Self-pollinated (Additive + Epistatic)
    5. Cross-pollinated – all 3.

 

  1. Progeny Test
    1. Self – make inbreds
    2. Test cross – In self pollinated crop to find recessives; in cross pollinated cross inbred with another inbred/hybrid/known population –for specific combining ability
    3. Top cross – Test inbred with open pollinated variety for general combining ability

 

  1. Inbreeding depression- Problem, reduced vigor, size

 

 

 Synthetics

 

Intercross two or more inbreds via open pollination.  Usually 8-16 lines. 

 

1946    “Stiff Stalked” corn synthetic - 16 lines

SYN1 - highest yield

SYN2 - little yield reduction

SYN3 - stable yield

 Sometimes natural selection will change composition-disease, drought, winterkill.

Synthetic used for alfalfa - grasses

Synthetic used by farmers who do not want to buy seed each year.

Marginal corn areas

Synthetics need to be constituted after several years.

 

Synthetic Cultivar

1. Constituted from reproducible units of cross-pollinated crop (clones, inbreds)

2. Materials used are selected from performance in combining ability or progeny tests

3. The cultivar is constituted by random intermating of the units

4. The component units are maintained so synthetic can be reconstituted           

 

Starting with Source Nursery

-> Several thousand plants. Develop inbreds

                 Superior plants inbred to fix traits

            –>25/50 superior clones grown in isolation

                           Self each, Intermate (polycross), Seed is bulked by clone


Superior clones identified in progeny test

–> 4-10 clones put together as synthetic.  Bulked as SYN0

Equal quantities of seed harvested from each clone/plant

 

SYN1 Open pollinated

 

Synthetics used in 1.) marginal areas where hybrids too costly, 2.) farmers can not buy seed every year, 3.) hybrid systems not available, and 4.) alfalfa, corn, sugar beets and sunflower.

 

Breeder maintains SYN0 parents.

 

 Breeding Strategies

  1. Mass Selection/open pollinated
    1. Good for oil, maturity, disease, insect
    2. Plants selected and bulked
    3. Weakness – unknown pollen source
    4. Will get inbreeding depression if too narrow genetic base
  2. Vegetative propagated
  3. Recurrent Selection
    1. Select good plants and programmed intermating
    2. Use progeny test to identify good plants
    3. Several cycles
  4. Hybrids
    1. 4 way, 3 way and single cross (highest yielding)
  5. Synthetics

 

 

  Hybrids – used to use T Cytoplasmic male sterility S/C CMS – Southern Corn leaf blight – reverted to machine emasculation.

·        ·        Single cross 75% A x B

·        ·        Highest yielding modified single (A x A') x B

·        ·        3 way cross 20% (A x B) x C

·        ·        Double cross (A x B) x (C x D) marginal areas

 

Corn yields in 1930=20 bu/acre   1995 – 140 bu/acre    59% genetics- 23% weed control-19% fertilizer

 

Flint, dent, sweet corn, floury, popcorn and waxy corn.

 

Corn production 247 MT USA, 125 MT China, Bz 33 MT

 

QPM – Quality Protein Maize- twice the lysine and tryptophan.  15% corn acreage in Ghana is QPM.

 

Reid Yellow Dent became very popular US variety.  First major US hybrids US 13(1919) and Iowa 939.

 

1908 – East planted hybrid and got 202 bu/acre.

1915 – Funk Bros. Stated hybrid corn breeding program.

1918 – First double hybrid produced

1920 – Henry Wallace started a corn breeding program. Pioneer Hi-bred

1992 – 250 private hybrid seed companies.  22 million bags of hybrid seed sold- $60/bag.

 

HFCS – High fructose corn syrup replaced sugar as major sweetener in the US.