Evaluation of efficiency and optimization of marker-assisted selection methods

讨论了基于标记的选择(MBS)在提高作物自交育种中的效率的有效性，即加速世代批量育种(GAB)。基于与理想性状基因连锁的DNA标记，推测MBS在F2和F3世代中起作用。MBS的有效性是基于其对增加所需基因被选择的概率的贡献来评估的。我们的概率计算表明，MBS的有效性取决于与育种目标有关的性状基因的数量以及可用标记的数量；当与育种目标有关的基因超过12个，并且这些性状基因中有几个或更多的标记可用时，MBS将是非常有效的。在这种情况下，MBS是有用的，即使只有100株在F2和F3世代被测试，而传统的GAB为了加速世代而种植2000株。当理想性状基因之间存在排斥连锁时，MBS的有效性增加，而当存在偶联连锁时，MBS的有效性降低。虽然共显性标记在大多数可能的条件下是优越的，但当与育种目标有关的基因相对较少，大约少于12个，并且理想性状基因在耦合阶段普遍连锁时，显性标记(与理想性状基因连锁)可能更优越。当MBS以多个共显性标记为基础时，扩大标记类型的选择范围是很重要的，不仅要选择最好的，而且要选择第二和第三好的、部分杂合型。当有足够多的标记可用时，性状基因和标记之间的联系不需要是完美的。

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.