| Budget Amount *help |
¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 2004: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 2003: ¥800,000 (Direct Cost: ¥800,000)
Fiscal Year 2002: ¥1,400,000 (Direct Cost: ¥1,400,000)
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| Research Abstract |
The effectiveness of marker-based selection (MBS) for increasing the efficiency of one of the most commonly used breeding methods of self-fertilizing crop plants, i.e., the generation-accelerated bulk breeding (GAB), is discussed. MBS is assumed to be operated in F_2 and F_3 generations based on DNA markers that are linked with desirable trait genes. The effectiveness of MBS is evaluated based on its contribution for increasing the probability of the desired genotype being selected. Our calculations of the probability show that the effectiveness of MBS depends on the number of trait genes concerned with the breeding objective as well as the number of available markers ; MBS will be highly effective when more than about 12 genes are concerned with the breeding objective and markers are available for several or more of these trait genes. In such a case, MBS is useful even with as few as 100 plants being tested in F_2 and F_3 generations, compared to a conventional GAB in which 2000 plants are grown for generation acceleration. The effectiveness of MBS increases in the presence of repulsion linkage between desirable trait genes, whereas decreases in the presence of coupling linkage. Although codominant markers are superior in most practically possible conditions, dominant markers (linked with desirable trait genes) could be superior when relatively few, roughly fewer than 12, genes are concerned with the breeding objective and desirable trait genes are linked prevalently in coupling phase. When MBS is based on more than several codominant markers, it is important to widen the range of marker genotypes to be selected; not only the best but also the second and third best, partially heterozygous genotypes should be selected. Linkage between trait genes and markers needs not to be perfect when sufficiently many markers are available.
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