Breeding and genetics of two new amphiploid Festulolium synthetics with improved yield and digestibility

In order to introduce drought tolerance and improved cell wall digestibility from fescue in fodder ryegrasses, we developed two amphiploid Festulolium synthetics. One is a synthetic composed of three selected drought tolerant F1 hybrid genotypes from a cross between tetraploid Lolium multiflorum and hexaploid Festuca arundinacea, further on called LMFA. The other is a synthetic composed of five selected genotypes with soft leaves from a cross between tetraploid Lolium perenne and tetraploid Festuca pratensis, further on called LPFP. We produced seeds in polycrosses of two generations of both amphiploids, i.e., syn1 and syn2, and tested them in plot trials to determine the yield and fodder quality. The syn1 of both Festulolium populations had a higher annual dry matter yield than the reference Lolium cultivars and Festulolium cultivars composed of the same parental species. However, the syn2 of LMFA did not show an improved drought tolerance during a dry growing season compared to other Festulolium cultivars, and the seed yield of LMFA syn1 was low and dropped extremely in syn2. The number of chromosomes of LMFA also decreased gradually from F1 to syn2, and there was a clear shift in chromosome composition towards the Lolium genome. The LPFP synthetic performed better. Although the sugar content was significantly lower than the sugar content of the perennial ryegrass cultivars, organic matter digestibility (OMD) of LPFP was as high as OMD of the tetraploid perennial ryegrass cultivars. The cell wall digestibility (NDFD) of LPFP was significantly higher than the NDFD of both parental species and higher than the NDFD of all tested Festulolium cultivars. The seed yield of LPFP was the same in syn1 and syn2. The chromosome number remained on average the same and no clear shift of the chromosome composition to one of the composing genomes was observed. Overall, chromosome analysis revealed a high number of aneuploidy in syn1 and syn2 generations of both LMFA and LPFP and a lot of variation in number of Lolium, Festuca and recombinant chromosomes, and in the Lolium:Festuca genome ratio was observed among different genotypes of the same population. Therefore, selection for genotypes with a more stable genome composition will be a prerequisite for a sufficient seed yield and a broader exploitation of these new Festulolium synthetics.