Bernardo Rex
Department of Agronomy and Plant Genetics, University of Minnesota, Saint Paul, USA.
Theor Appl Genet. 2025 Feb 2;138(2):42. doi: 10.1007/s00122-025-04831-0.
Improving a hybrid by transferring partially dominant alleles from one parent to the other is feasible if the median level of dominance is moderate and prediction accuracy is high. Convergent improvement within a P × P single-cross hybrid attempts to transfer partially dominant favorable alleles from P to P and from P to P. My objective in this simulation study was to determine if convergent improvement is a feasible procedure to develop a better single cross. Heterozygote effects (d) and homozygote effects (a) at quantitative trait loci (QTL) were resampled from an empirical distribution of genomewide marker estimates of d and a for maize (Zea mays L.) grain yield. The d values were scaled (d scale = 30%, 45%, and 60%) to account for the known upward bias when d/a ratios at markers are used to estimate d/a ratios at QTL. Convergent improvement led to positive responses to selection when only 30 QTL controlled the trait. When 250 QTL controlled the trait, convergent improvement led to a positive response when the d scale was 30% but not when the d scale was 60%. For the intermediate d scale of 45%, responses were positive in later backcross generations and when prediction accuracy was 0.60 or 0.80. The largest response was achieved with only one cycle of genomewide recurrent selection; additional cycles compromised the gains achieved from the final step of phenotypic selection among single crosses. Overall, the results suggested that success in convergent improvement is a possibility but not a certainty in maize, and that more consistent results would be expected in species such as rice (Oryza sativa L.) that show weaker heterosis than maize.
如果显性的中位数水平适中且预测准确性较高，那么通过将部分显性等位基因从一个亲本转移到另一个亲本以改良杂交种是可行的。在P×P单交杂种内进行聚合改良试图将部分显性有利等位基因从P转移到P以及从P转移到P。我在这项模拟研究中的目标是确定聚合改良是否是培育更好单交种的可行方法。数量性状位点（QTL）处的杂合子效应（d）和纯合子效应（a）是从玉米（Zea mays L.）籽粒产量的全基因组标记估计值的经验分布中重新抽样得到的。对d值进行了缩放（d缩放比例 = 30%、45%和60%），以考虑使用标记处的d/a比率来估计QTL处的d/a比率时已知的向上偏差。当只有30个QTL控制该性状时，聚合改良导致对选择产生正向响应。当有250个QTL控制该性状时，d缩放比例为30%时聚合改良导致正向响应，但d缩放比例为60%时则不然。对于45%的中间d缩放比例，在回交后代后期以及预测准确性为0.60或0.80时响应为正向。仅通过一个全基因组轮回选择周期就实现了最大响应；额外的周期会损害单交种之间表型选择最后一步所获得的增益。总体而言，结果表明在玉米中聚合改良有可能成功，但并非必然，并且在诸如水稻（Oryza sativa L.）等杂种优势比玉米弱的物种中预计会得到更一致的结果。
