Effects of Mass Selection on Maize Synthetic Populations

For evaluating the effects on improvement of different maize (Zea mays L.) synthetic populations, genetic parameters derived from simple sequence repeat (SSR) markers were statistically analyzed with maize synthetic populations GP3, GP4, and GP5 after 4 cycles of mass selection. Genetic differences were observed in most traits across populations or cycles, and the interaction between population and cycle was significant. The genetic gains ranked as GP3 < GP5 < GP4 for kernel depth and as GP3 > GP5 > GP4 for row number per ear. Means of kernel depth and row number per ear were obviously increased after 4 cycles of mass selection, showing significantly direct responses to selection. Plant height and ear height were enhanced by selection, and the increment in GP4 was significantly higher than that in GP3 and GP5. The genetic gains of yield per plant and ear diameter were higher in GP4 than in GP3 and GP5. In all populations, most yield traits were improved in cycle C4 compared to those in cycle C0, showing a significant correlated response. Except for plant height and ear height, the other traits showed significant variations in GCA, and the GCA effects of GP5 in most yield traits were higher than those of GP3 and GP4. In most yield traits, the GCA effects tended to increase with the progress of population improvement through mass selection. Testcross combinations with yield per plant more than 8% over the controls were derived from the cycle C4, showing a significantly indirect response to mass selection. The variation coefficients of phenotypic traits varied slightly across selection cycles. The genetic similarity based on SSR data showed slight increases in GP3 and GP4, but relative stability in GP5. With the increase of selection cycle, the genotype number in derivatives had small reductions in GP3 and GP4, but an increase tendency in GP5. These results indicate that mass selection is not only effective for population improvement but also maintained the genetic diversity of the population. The effect of genetic improvement varied across populations of traits.

摘 要基于田间试验的统计分析和SSR分子标记的遗传参数评估, 分析了3个玉米人工合成群体GP3、GP4和GP5经4轮控制双亲混合选择的改良效应。结果表明, 多数性状在不同群体及不同轮回间存在真实的遗传差异, 粒深遗传增益以GP4＞GP5＞GP3, 穗行遗传增益以GP3＞GP5＞GP4, 各个群体C4的粒深、穗行均值都显著或极显著大于C0, 直接选择效应显著; 株高和穗位高随选择周期增加呈明显增加趋势, 且GP4的增幅显著大于GP3和GP5, 单株产量及穗粗的遗传增益以GP4大于GP3和GP5, 各群体多数产量性状的均值以C4显著大于C0, 相关选择效应显著; 除株高、穗位高外, 其他性状GCA变异群体间差异达显著或极显著水平, GP5多数产量性状的GCA优于GP3和GP4, 各群体多数产量性状的GCA效应值随改良进展呈增加趋势, 对照优势大于8%的大部分测交组合均为各群体C4所配组合, 间接选择效应显著; 随改良世代进行, 群体部分性状的表型变异系数虽有所减小, 但变化幅度不大; 基于SSR分子标记估算的群体内遗传相似系数, GP3和GP4改良后代呈略增趋势, GP5变化不大, 对于群体基因型数, GP3和GP4随改良代数增加呈略减趋势, GP5呈略增趋势。上述结果说明, 适度控制双亲混合选择在有效改良群体的同时, 还能较好地保持群体的遗传多样性, 但不同基础群体及不同性状间, 其改良效应存在一定的差异。