Application of molecular markers in selected breeding material and plant genetic resources of Lolium perenne L.
by Siyang Liu
Date of Examination:2015-05-12
Date of issue:2016-01-06
Advisor:Prof. Dr. Heiko C. Becker
Referee:Prof. Dr. Gunter Backes
Referee:Prof. Dr. Johannes Isselstein
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EnglishOut-crossing perennial ryegrass (Lolium perenne L.) is the most important forage grass species in temperate regions. It is also proposed as a sustainable source of biomass for energy production. However, the improvement of yield of perennial ryegrass in the past years is not comparable to that of the other crops. The utilization of hybrid breeding and the application of markers are therefore anticipated to boost the breeding of perennial ryegrass. The objective of the present study is to investigate the genetic diversity and the presence of heterotic pools in selected L. perenne material by applying molecular markers and the potential applications of molecular markers in L. perenne hybrid breeding. For these purposes, 1384 DArT, 182 SNP and 48 SSR markers were applied to 297 perennial ryegrass accessions. A bulk sampling strategy with 30 individuals per bulk sample was employed and proofed to be efficient in distinguishing L. perenne accessions. Within the 297 accessions, high polymorphism rate was revealed for all the marker types: in DArTs, SNPs and SSRs, 1.99, 2.00 and 8.20 alleles per locus in average were obtained; The JD (Jaccard distance) for DArT markers ranged from 0.00 to 0.73 with an average of 0.45; the MRD (Modified Roger`s distance) for SNPs ranged from 0.03 to 0.52 with an average of 0.34; the MRD for SSR markers ranged from 0.26 to 0.76 with an average of 0.54. Genetic diversity for dominant DArT and co-dominant SNP and SSR markers was found to be 0.26, 0.32 and 0.45, respectively. All the marker types are suitable for the diversity study and DArT markers showed the highest discriminative ability, consistency and reproducibility. The resulting data was evaluated with different classification methods, but no clear structure was found. Subsequently a subset of the plant material containing nine CMS accessions and 76 pollinators was used to produce the hybrids and conduct the field trial. Parental accessions as well as their derivative hybrids were arranged in two sowing years (the 2010 sowings and the 2011 sowings) and FMY (fresh matter yield) and DMY (dry matter yield) were recorded across five locations. For FMY, the average MPH (Mid-parent heterosis) was found to be 13.88% and 3.24% for diploid hybrids in both sowings and 6.85% for tetraploid hybrids; the average BPH (Better-parent heterosis) was 3.23% and -1.10% for diploids in both sowings and 4.94% for tetraploid hybrids. The pattern of DMY is similar to that of FMY. We further calculated the correlation between MPH and genetic distances estimated from molecular markers. In most cases, positive but weak correlations were observed. Therefore the prediction of heterosis solely based on genetic distances might not provide very accurate results. Our results suggested a lack of heterotic patterns in the tested material. Further investigations on the hybrid breeding should be aimed at the identification of heterotic pools. The application of molecular markers might serve as an efficient tool in assisting this process.
Keywords: lolium perenne; SSR; DArT; SNP; genetic diversity; heterosis