Stability of Genome Composition and Recombination between Homoeologous Chromosomes in <b><i>Festulolium</i></b> (<b><i>Festuca × Lolium</i></b>) Cultivars

Abstract

Festulolium are hybrids between fescue (Festuca) and ryegrass (Lolium) species and combine high seed yield of ryegrasses with abiotic stress tolerance of fescues. Chromosomes of Festuca and Lolium present in Festulolium freely pair and recombine, which results in highly variable progeny where every single plant has a unique chromosome constitution. Thus, the stability of the genomic composition in Festulolium cultivars is an important issue. In this work, we used in situ hybridization to examine the genomic composition (understood as the proportion of parental genomes present) over 3 consecutive generations of propagation via outcrossing (the first one being the generation used for cultivar registration) of 3 Festulolium cultivars. Our analysis revealed that the genome composition largely differs among the plants from individual cultivars but appears to be relatively stable over the generations. A gradual shift in the genome composition towards Lolium observed in the early generations of hybrids appears to reach a plateau where the proportions of parental genomes become stabilized. Nevertheless, the proportion remains unbalanced to a certain extent (always in favor of the Lolium genome) in each cultivar. Our observations indicate a possibility to modulate genomic composition in hybrids by breeders' selection without a compromise on stability.

Selective Elimination of Parental Chromatin from Introgression Cultivars of xFestulolium (Festuca × Lolium)

“…In our previous work, we confirmed that amphiploid L. multiflorum × F. pratensis cultivars were relatively stable over three consecutive generations. Despite a large variability within the populations, the genomic composition did not change significantly, and the Festuca chromatin was not eliminated any further [18]. Similarly, Zwierzykowski et al reported that chromosomes of F. pratensis were gradually replaced by those of L. multiflorum in six consecutive generations of hybrids but became stabilized in the F7-F8 generations without any additional elimination of Festuca chromatin [20].…”

“…The continuity of Festuca-chromatin elimination in advanced breeding material is questionable. In our previous work, we analyzed three consecutive generations of three registered amphiploid xFestulolium cultivars [18]. We found that despite high genetic variability within each population, the proportion of parental genomes was relatively stabilized without apparent Festuca-chromatin elimination in subsequent generations.…”

Cytogenetic insights into Festulolium

“…While amphiploids display relatively stable genome composition and no further shifts towards Lolium genome, elimination of introgressed segment(s) has been observed in the introgression forms. Stabilization of the hybrid genome in amphiploid cultivars is observed at about 2:1 proportion of Lolium vs. Festuca chromosomes (Kopecký et al 2017). This ratio probably creates optimal combinations of parental alleles and the highest heterosis.…”

“…Despite the formation of quadrivalents and meiotic irregularities leading to frequent aneuploidy (up to 80 % in cvs. Hostýn and Perseus), fertility is high and seed set is sufficient for commercial production (Ghesquiere et al 2010, Kopecký et al 2017.…”

“…On the contrary, Perseus was developed by selection of plants from Perun, primarily for use in Western Europe and with high seed yield, late heading date, and high dry-matter yield. Thus, its genome composition with a higher proportion of the Lolium chromatin can be expected (Kopecký et al 2017). Cv.…”