INTRODUCTION TO PLANT BREEDING

AGRONOMY 815 / COURSE NOTES

P. STEPHEN BAENZIGER, 338 Keim Hall, 472-1538

DEPARTMENT OF AGRONOMY / UNIVERSITY OF NEBRASKA

VARIETY BLEND

Variety Blend = mechanical mixture of seed of two or more varieties.

Rational . . . A mixture of genotypes will have a buffering effect against genotype-environment interaction and will be more stable over locations and years than a single variety.

DISADVANTAGES:

  • Variety blends will be less uniform than a pure line variety even though one would have selected for uniform maturity, etc.


  • Also, as the number of varieties in the blend is increased, the mixture will never be as high yielding as the highest yielding variety in the mixture.


  • Variety blends must be reconstituted regularly to maintain stability.


    • MIX AND MATCH BREEDING:

    These self pollinated methods are not mutually exclusive. Most breeders do not use any single method. Some practical examples are:

    1. Begin with a pedigree up to F3 or F4 (heavy cull obvious poor types), then use single seed descent for two generations (F5 and F6) in a winter nursery so that F7 lines can be yield tested in the next summer.


    2. Begin with a pedigree breeding method with heavy selection on disease resistance, one year the disease is absent -- harvest all of the selected lines in a bulk and maintain them as a bulk until the disease lets you separate out the resistant plants again.


    3. Select heavily, as you would with pedigree breeding, in the F2 or F3 and then use single seed descent or doubled haploidy to make homozygous lines for yield testing.


    4. Begin with a bulk, in the F2 and F3 test at multiple locations and determine which bulks have the best potential for line development, then begin pedigree selection within the selected bulks.


    5. Derive a small number of doubled haploid lines from the F1 plants that are used to make bulks. While advancing the bulks, test the doubled haploids at multiple sites to determine which bulks should have the highest mean and most variation. Save bulks on the basis of doubled haploid performance. This procedure would be done in crops where it is very difficult to make doubled haploid lines.


    6. Breed using the pedigree system, but also grow small bulk populations so that if the pedigree lines are lost to hail or some other natural disaster, the bulk populations can be used for selection.


    Land Varieties (endemic mixture of types well adapted to a particular region) were the early 'populations' from which new cultivars were derived.