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Problems need to be considered in molecular breeding of wheat

With the development of molecular genetics, crop modification became more exact and precise. Some problems ignored in traditional genetics and breeding in the past have been emerged. The prestige of molecular breeding will be greatly affected if not paying attention to these issues.

Australia-China Wheat Genetics and Breeding Workshop, May 24-26, 2010

Problems need to be considered in molecular breeding of wheat

Wang Haibo

Plant Genetic Engineering Center, Institute of Genetics and Physiology, Hebei Academy of Agriculture and Forestry Sciences, Shijiazhuang 050051

With the development of molecular genetics, crop modification became more exact and precise. Some problems ignored in traditional genetics and breeding in the past have been emerged. The prestige of molecular breeding will be greatly affected if not paying attention to these issues.

1. A variety can not develop to a pure line as one genotype by selfing with traditional methods

Theoretically, a pure line of wheat can be obtained by self-pollination and selection, but it is impossible in practice. Biological traits can be classified as distinguishable traits and non-distinguishable traits. The distinguishable traits can be further divided into visible traits and non-visible traits, and most of the traits are non-visible. Even for the visible traits, only a few has been well-manipulated. If the traits are unclear, they can not be selected and can not be investigated at molecular level correctly and corresponded to the right DNA sequences either. The genome of wheat is huge. Genes are not only located on different chromosomes, but also exchangeable between the homologues. It results in enormous numbers of gametes and homozygous types. The probability of heterozygosity among alleles is 50%, while the events of combination of non-allelic genes would be nearly infinite. Thus, a variety of wheat can not develop to a real pure line with traditional methods. The near-isogenic lines can not be produced through backcrossing with such a kind of variety. For molecular genetic and molecular marker research, it badly needs double haploid as the recurrent parent.

2. Molecular breeding facing a serious challenge of background constraints

The results are usually undesirable in molecular breeding, whether it come from genetic transformation or marker-assisted selection or molecular design. The target gene could not display the expected role because it does not match the genetic background well. In the past, the function of genetic background is usually consciously avoided since it is very complicated. To carry out the research of genetic background and gene sociology is urgently needed. Pollen plays an important role in background-genetics. Based on continuous backcrossing, to compare the high-resolution molecular map between different generations and their corresponding pollens, some patterns of background-genetics and the interaction of target gene with the background can be found.

3. The gene of Mendelian factor much complicated than DNA sequence

According to Mendel’s idea, traits are always correspond to genes, the Mendelian factor equals to gene. At the molecular level, gene is a specific DNA sequence. However, variation in DNA sequence not necessarily reflected in a trait. Mutant-genetics have shown that thousands of DNA sequence variations sometimes only show a few phenotypes; while a large number of different genetic traits usually have small differences at DNA level. Although it can be explained with the concepts of coding region and non-coding region, it is not inclusive. In fact, only in a few cases, specific DNA sequences equal to Mendelian factor. The content of Mendelian factor is more than DNA sequence. Mendelian factor = [Specific DNA sequences] × [background complexity + 1]n, where n reflects the complexity of the expression mechanism, n≥0. It is obvious that Mendelian factor is much complicated than DNA sequences. The knowledge of traits is from the understanding of the effect of Medelian factor, but in many cases it is quite hard to find the causal relationship between trait and DNA sequence.

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