PLANT BREEDING TERMINOLOGY AND SYMBOLS Plant breeders are

PLANT BREEDING TERMINOLOGY AND SYMBOLS Plant breeders are a group of professional separated by a common language It needs to be recognized that few plant breeding programs share the same terminology in describing generations, families, lines, plots and other trappings. Desperation ! Dislocation ! Separation ! Condemnation ! Isolation ! Desolation ! ‘Bad’-- U 2

All communications will be through the two-tiered system outlined by Fehr (1987). It is the most commonly understood system, theoretically correct, and makes ambiguity almost impossible. Ambiguity--The Example of the F 1 Generation Cross between Homozygous parents (A 1 A 1 x A 2 A 2) Heterozygous parents (A 1 A 2 x A 3 A 4) Homogeneous F 1 progeny Heterogeneous F 1 progeny A 1 A 2 A 1 A 3 A 1 A 4 A 1 A 2 A 2 A 3 A 1 A 2 A 2 A 4

Ambiguity: The Example of the F 2 and S 0 Generations The symbol F refers to the word ‘filial’, and the subscript to the generation in the sequence of generations following a cross (F 1, the first generation after the cross; F 2, the second generation after the cross, etc. ). The F symbol is usually, but certainly not always, used with reference to self-pollinated generations of a self-pollinated species.

Ambiguity: The Example of the F 2 and S 0 Generations The symbol F refers to the word ‘filial’, and the subscript to the generation in the sequence of generations following a cross (F 1, the first generation after the cross; F 2, the second generation after the cross, etc. ). The F symbol is usually, but certainly not always, used with reference to self-pollinated generations of a self-pollinated species.

Ambiguity: The Example of the F 2 and S 0 Generations The F 2 generation is the first segregating generation after the cross between two inbred lines. Because the parents were homozygous inbreds, a generation of selfing (F 1 F 2) was necessary to produce this 1: 2: 1 ratio.

The familiar 1: 2: 1 phenotypic ratio is observed at loci in the S 0 generation if two contrasting alleles at a locus are each present at a frequency of 0. 5. The S 0 generation, like the F 2 generation, is the first segregating generation after the cross. (It is also the first generation after the cross in this case. ) But in contrast to the F 2, a generation of selfing is not necessary in order to produce the 1: 2: 1 phenotypic ratio. This is due to the fact that the parents making the cross are not only homozygotes.

Parents Thus the S 0 generation is equivalent in terms of genotypic frequencies to the F 2 generation resulting from the cross between homozygous inbred parents. Seed obtained through random mating could technically be called F 1 seed, but, because the genotypic frequencies in the population of hybrids obtained by random mating resembles an F 2 generation, we will refer to it as S 0 seed.

Many theoretical studies begin with a reference or base population which is heterozygous and heterogeneous and contain two alleles per locus at frequencies of 0. 5. This base population is referred to as the S 0 or F 2. With systematic schemes of inbreeding, it follows that: F 3 S 1 F 4 S 2 F 5 S 3 F 6 S 4 Other side of argument, S 0 = F 1, because neither has undergone systematic self-pollination

Symbolism for Describing the Inbreeding of Lines from an F 2 or S 0 Population The two-tiered system we utilize is applicable for both F and S inbreeding situations. The generalized formula is written as: Fx: y or Sx: y where x was the generation of the single plant that was harvested, separately, giving rise to the derived line, and y is the current generation of inbreeding of the plants within this derived line.

We are concerned about both values, x and y, because together they permit us to estimate the expected genotypic composition of the derived line at loci for which the parents had contrasting alleles.

Note that ‘F 2: 3 line’ is an abbreviation for ‘an F 2 -derived line in the F 3 generation’. Note that ‘S 0: 1 line’ is an abbreviation for ‘an S 0 -derived line in the S 1 generation’.

The key to learning this system is to always identify the most recent generation in which a single plant was harvested to give rise to the current line of descent. For example, for the F 2: 3 line, its single plant origin was in the F 2 generation. For the F 2: 4 line, its single plant origin was the same F 2 plant, because a bulk of several plants was harvested in the F 3 generation. However, the situation is different for the F 4: 5 line. The most recent generation in which a single plant was harvested to give rise to this line was the F 4 generation.

. Similarly, for the S 1: 2 line, the most recent generation in which a single plant was harvested to give rise to this line was the S 1 generation. For the S 1: 3 line, the same plant is the single plant origin because a bulk of several plants was harvested in the S 2 generation. If a single plant within this S 1: 3 line is selected, selfed, and the seed from the selfed ear is kept separate, then you would have S 3: 4 seed in the envelope.