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The proverb ‘The apple doesn’t fall far from the tree’ is used both in the English and Dutch language to describe that children will grow up very similar to their parents in the way they act and
their physical abilities. The causal basis for this observation has, in the case of humans, both a genetic and environmental component to it. Luckily for wheat we only really have to worry about the genetic
contribution of the parents.The title and the proverb came to mind as a grower complained that I had omitted to give full disclosure about the parents of a particular variety he had chosen to grow and had less than
stellar experiences with. He blamed this experience on the experiences he had had with one of the parents in the pedigree of that particular variety. This begged the question as it is posed in the title.
Now before I list the pedigrees of a number of popular hard red spring wheat varieties, we just need to explore some genetic theory
and concepts in plant breeding. The job of a plant breeder in its essence is very simple and straightforward: accumulate as many positive traits into a single variety as possible and do this in the shortest amount
of time possible.
The outward appearance of a plant is commonly referred to as its phenotype. The characteristics of this phenotype are the product of
its genetic make-up. Simple traits, hereafter referred to as qualitative traits, are controlled by a single gene or piece of genetic code on a chromosome. An example of a simple trait is the presence of a particular
leaf rust resistance gene. In the absence of the gene, the wheat variety will be susceptible to the races of leaf rust for which the leaf rust gene confers resistance. In the presence of this gene, the variety will
be immune to the disease. More often than not, traits are not simply inherited. These so-called quantitative traits are controlled by multiple genes of which we cannot measure the individual effect on the phenotype
of the cultivar. Grain yield, test weight, grain protein are a few examples of such quantitative traits.
Now when a wheat breeder makes a cross between two varieties, the first generation offspring or F1 is the complete sum of both parents. In other words, all traits that either parent contributed are present in the DNA. Some of these traits will not be
visible in the phenotype. In genetic terms, this is called recessive and means that a different version of the gene (also known as an allele) is expressed such that the other form of the gene is not seen
phenotypically.
Fortunately or unfortunately, wheat breeders do not sell F1 hybrids like corn breeders. Instead they develop pure lines. Pure lines are derived from the initial F1 generation through
repeated self pollination (wheat is by nature a self pollinating species). This process takes about 6 to 7 generations. It is during these 6 to 7 generations that something very important takes place every single
time the plant produces its gametes (egg cells and pollen grains). In a process called meiosis (or reduction cell division) the chromosomes that were inherited from either of the parents not only are randomly
redistributed to the gametes, there is also a good chance that complete segments of chromosomes get exchanged between pairs of homologous chromosomes. This phenomenon is known as crossing-over and is crucial for
breeders to continue to make progress as the outcomes of crossing-over are new combinations of the different genes previously unseen. The art and science of plant breeding is to be able to recognize these new
combinations.
Coming back to the title; the proverbial apple may fall closer to mom or dad and anywhere in between and it is even possible that the
apple falls farther away and exceeds either parent. These transgressive segregants are the pearls that breeders look for. Unfortunately, that is easier said than done. An example of that is the resistant FHB
resistance of RB07. Neither HJ98 nor Norlander were varieties that were known for their resistance to FHB. Both were actually rather poor. RB07, however, is rated a solid 5 and comes close to a 4. That is quite
surprising if you look at the pedigree. On the other hand, Oklee did inherit its poor mixing characteristics from one of its parents, namely 2375.
In table 1 are a number pedigrees listed for common HRSW. Breeders use common system to describe the pedigree of a variety. A ‘/’
mark indicates a cross between two lines. The mother is always listed first, the father/male parent is listed second. A ‘/#/’ simply indicates the order of crossing and allows a breeder to list more than one
generation. For example if we look at the pedigree of Freyr, Sonja was crossed with Vance. A line selected from that cross was crossed with Sumai 3 as father. The outcome of that cross was crossed with Dalen. In
other words, the maternal grandparents of Freyr are Sumai 3 and the line that was selected from the cross Sonja/Vance which are the maternal great grandparents to Freyr.
In summary, having the pedigree of a variety doesn’t mean you learn all there is to know about the variety and is not a perfect
predictor of the performance of a variety.
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