Perennial ryegrass (Lolium perenne L.), an important forage grass species in temperate regions, is genetically improved by population breeding. Although valued for their broad genetic base, the resulting synthetic varieties only partially exploit heterosis. Hybrid breeding offers opportunities to fix beneficial heterotic patterns more effectively and, hence, to increase the yield potential. A suspected bottleneck in the production of perennial ryegrass hybrids is the genetic intermixture of existing germplasm, impeding the definition of heterotic groups. In this study, selected parental populations of a diploid and tetraploid cytoplasmic male sterility (CMS)-based hybrid breeding program were characterized using genotyping-by-sequencing (GBS). Hybrid populations, derived from 26 parental combinations of the tetraploid breeding program, were tested for yield performance and compared to synthetic varieties at five sites over four growing seasons. The hybrids significantly outperformed the synthetics by 4.15% on average for total dry matter yield. Additionally, GBS revealed the existence of sub-populations within the tetraploid CMS germplasm. This sub-population structure represents the untapped potential that could be exploited for heterosis to further increase biomass yields. Here, we show that CMS hybrids generate substantial yield gains in perennial ryegrass and provide a method to further improve hybrid breeding, using GBS to select for heterotic groups.

中文翻译：

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为多年生黑麦草的成功杂交育种开发杂种优势群体

多年生黑麦草（黑麦草perenneL.）是温带地区重要的牧草种，通过种群育种在遗传上得到改善。尽管因其广泛的遗传基础而受到重视，但所得合成品种仅部分利用杂种优势。杂种育种提供了机会，可以更有效地修复有益的杂种模式，从而提高单产潜力。多年生黑麦草杂种的生产中一个可疑的瓶颈是现有种质的遗传混合，阻碍了杂种群体的定义。在这项研究中，使用基于序列的基因分型（GBS）来表征基于二倍体和四倍体细胞质雄性不育（CMS）的杂交育种程序的选定亲本群体。来自四倍体育种计划的26个亲本组合的杂种种群，在四个生长季节的五个地点对产量进行了测试，并与合成品种进行了比较。杂种的总干物质产量显着优于合成纤维，平均高出4.15％。此外，GBS揭示了四倍体CMS种质内存在亚群。该亚群结构代表了尚未开发的潜力，可用于杂种优势以进一步提高生物量产量。在这里，我们显示了CMS杂种在多年生黑麦草中产生了可观的产量增长，并提供了一种进一步改进杂种育种的方法，使用GBS选择杂种群体。GBS揭示了四倍体CMS种质内存在亚群。该亚群结构代表了尚未开发的潜力，可用于杂种优势以进一步提高生物量产量。在这里，我们显示了CMS杂种在多年生黑麦草中产生了可观的产量增长，并提供了一种进一步改进杂种育种的方法，使用GBS选择杂种群体。GBS揭示了四倍体CMS种质内存在亚群。该亚群结构代表了尚未开发的潜力，可用于杂种优势以进一步提高生物量产量。在这里，我们显示了CMS杂种在多年生黑麦草中产生了可观的产量增长，并提供了一种进一步改进杂种育种的方法，使用GBS选择杂种群体。