Excellence in Breeding Platform, Consultative Group of International Agricultural Research, Texcoco, Mexico.
International Maize and Wheat Improvement Center (CIMMYT), Texcoco, Mexico.
Theor Appl Genet. 2023 Jun 8;136(7):147. doi: 10.1007/s00122-023-04377-z.
Reciprocal recurrent selection sometimes increases genetic gain per unit cost in clonal diploids with heterosis due to dominance, but it typically does not benefit autopolyploids. Breeding can change the dominance as well as additive genetic value of populations, thus utilizing heterosis. A common hybrid breeding strategy is reciprocal recurrent selection (RRS), in which parents of hybrids are typically recycled within pools based on general combining ability. However, the relative performances of RRS and other breeding strategies have not been thoroughly compared. RRS can have relatively increased costs and longer cycle lengths, but these are sometimes outweighed by its ability to harness heterosis due to dominance. Here, we used stochastic simulation to compare genetic gain per unit cost of RRS, terminal crossing, recurrent selection on breeding value, and recurrent selection on cross performance considering different amounts of population heterosis due to dominance, relative cycle lengths, time horizons, estimation methods, selection intensities, and ploidy levels. In diploids with phenotypic selection at high intensity, whether RRS was the optimal breeding strategy depended on the initial population heterosis. However, in diploids with rapid-cycling genomic selection at high intensity, RRS was the optimal breeding strategy after 50 years over almost all amounts of initial population heterosis under the study assumptions. Diploid RRS required more population heterosis to outperform other strategies as its relative cycle length increased and as selection intensity and time horizon decreased. The optimal strategy depended on selection intensity, a proxy for inbreeding rate. Use of diploid fully inbred parents vs. outbred parents with RRS typically did not affect genetic gain. In autopolyploids, RRS typically did not outperform one-pool strategies regardless of the initial population heterosis.
轮回选择有时会增加杂种优势显性的克隆二倍体的单位成本遗传增益，但通常对同源多倍体没有好处。通过育种可以改变群体的显性和加性遗传值，从而利用杂种优势。一种常见的杂种杂交育种策略是轮回选择（RRS），其中杂种的亲本通常根据一般配合力在池内循环。然而，RRS 和其他育种策略的相对表现尚未得到彻底比较。RRS 的成本相对较高，周期较长，但由于其利用显性杂种优势的能力，这些有时会被抵消。在这里，我们使用随机模拟来比较 RRS、终端杂交、基于育种值的轮回选择和基于杂交表现的轮回选择的单位成本遗传增益，考虑到不同程度的显性杂种优势、相对周期长度、时间跨度、估计方法、选择强度和倍性水平。在高强度表型选择的二倍体中，RRS 是否是最优的育种策略取决于初始种群杂种优势。然而，在高强度快速循环基因组选择的二倍体中，在研究假设下，几乎所有初始种群杂种优势下，在 50 年后，RRS 是最优的育种策略。随着相对周期长度的增加以及选择强度和时间跨度的降低，二倍体 RRS 需要更多的群体杂种优势才能优于其他策略。最优策略取决于选择强度，这是近交率的一个指标。使用二倍体完全自交亲本与 RRS 的杂交亲本通常不会影响遗传增益。在同源多倍体中，无论初始种群杂种优势如何，RRS 通常都不如单池策略。
