INTRODUCTION TO PLANT BREEDING

AGRONOMY 815 / COURSE NOTES

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

DEPARTMENT OF AGRONOMY / UNIVERSITY OF NEBRASKA

HYBRIDIZATION

Hybridization is necessary to bring about recombination and selection of genotypes different from those presently available.

The objective of hybridization in self pollinated species is to combine in a single genotype (usually a homozygous line but in the case of sorghum, for example, a hybrid), desirable genes that are found in two or more genotypes. One hopes to obtain transgressive segregates that are superior to the parental varieties.

Selection of parents determines the potential of a breeding program. Choice of parents is very important, i. e., garbage in, garbage out.

One parent is usually chosen for its proven performance in the area of intended use. The other parent(s) normally has some attribute(s) not possessed or expressed to the same degree by the first parent.

Must clearly define objectives before making the cross.

Breeder must also decide how to most effectively handle the segregating generations in order to achieve their goal.

Skill in making selections in segregating generations will determine whether the potential of the cross will be realized.

AN IMPORTANT POINT TO REMEMBER IS THAT EVEN IN THE MOST DIFFICULT CROP, MAKING THE CROSS TAKES MUCH LESS OF THE TOTAL TIME IN A BREEDING PROGRAM THAN ANY OTHER SINGLE OPERATION.

• In hybridizing two varieties of a self pollinated crop the plant breeder is concerned with:

  1. Limits and nature of the array of variability in the F2 segregating generation;


  2. Progress of the hybrid population towards complete homozygosity;


  3. The nature of the successful gene combinations.


• Factors affecting gene recombination in the F2:

  1. Number of genes differentiating the parents;


  2. Linkage of genes on the same chromosome;
    3. <

  3. Number of alleles of each gene.


Important to remember that when 2 pure-line varieties are crossed, the maximum number of gene combinations is achieved in the F2 (actually the combinations occur in the F1 plant at the time of fertilization) thus F2 populations should be as large as practically feasible.

With increasing numbers of selfing generations the proportion of homozygotes increases. It is easier for a plant breeder to find desirable homozygous types in later generations of hybrid populations of self-pollinated crops.

AN OLD BREEDER ONCE COMMENTED THAT IN SELF-POLLINATED CROPS YOU MUST INBREED AND SELECT. OF THE TWO, INBREEDING IS EASIER; THEREFORE, DO IT FIRST.