Lolium perenne L. is the most important forage grass species in temperate regions. It is also considered as a sustainable source of biomass for energy production. However, improvement in biomass yield has been limited by comparison with other major crops. More efficient utilisation of genetic resources and improved breeding schemes are required to advance L. perenne breeding. In an attempt to elucidate the extent of genetic diversity in L. perenne, 1384 DArT, 182 SNP and 48 SSR markers were applied to 297 accessions (Set I) contributed by three German breeding companies and the IPK Genebank. Due to the heterogeneous nature of Lolium accessions, bulk samples were used. Apart from germplasm set I, additional set II and set III was used to determine the reproducibility of marker system and judge the feasibility of bulk strategy in this study. By assessing different bulk sizes, 24 individuals per sample were shown to be a representative number of plants to discriminate different accessions. Among the 297 accessions, all marker types revealed a high polymorphism rate; 1.99, 2.00 and 8.19 alleles, were obtained per locus on average using DArTs, SNPs and SSRs, respectively. The Jaccard distance for DArT markers ranged from 0.00 to 0.73, the Modified Roger’s distance (MRD) for SNP markers ranged from 0.03 to 0.52, and for SSR markers from 0.26 to 0.76. Gene diversity for dominant DArT and co-dominant SNP and SSR markers was found to be 0.26, 0.32 and 0.45, respectively. DArT markers showed the highest consistency and reproducibility. The resulting data were evaluated using a number of different classification methods, but none of the methods showed a clear differentiation into distinct genetic pools. With regard to hybrid breeding, this will possibly impede substantial progress towards increased biomass yields of L. perenne by utilising heterosis.

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.

"Breeding of CMS-F1-Hybrids in Lolium perenne with improved nitrogen use efficiency" published on 01 Nov 2005 by Wageningen Academic.