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

Abstract

Alien chromosome introgressions can be used to introduce beneficial traits from one species into another. However, exploitation of the introgressions in breeding requires proper transmission of introgressed segments to consecutive generations. In xFestulolium hybrids chromosomes of Festuca and Lolium readily pair and recombine. This opens a way for introgression of traits (e.g., abiotic and biotic stress resistance) from Festuca into elite Lolium cultivars. However, retention of Festuca chromatin in xFestulolium is uncertain as several studies indicated its gradual elimination over generations of sexual reproduction. Here we investigated genome composition in two subsequent generations of four introgression xFestulolium (F. pratensis × L. multiflorum) cultivars using genomic in situ hybridization. We observed about 27–32% elimination of Festuca chromatin in a single round of multiplication. At this pace, Festuca chromatin would be completely eliminated in about four generations of seed multiplication. On the other hand, we observed that it is possible to increase the proportion of Festuca chromatin in the cultivars by proper selection of mating plants. Nevertheless, once selection is relaxed, the first round of the seed multiplication reverts the genome composition back to the Lolium type. Thus, it seems that amphiploid forms of xFestulolium with relatively stable hybrid genomes may be more promising material for future breeding than introgression lines.

Cytogenetic insights into Festulolium

“…However, chromosomes 2F, 4F, 5F, and 6F were eliminated more frequently than the remaining three Festuca chromosomes. Similarly, Kopecký et al (2019) found that chromosome 5F Fig. 2.…”

“…This ratio probably creates optimal combinations of parental alleles and the highest heterosis. On the other hand, introgression cultivars appear to be highly unstable and a reversion to the parental (Lolium) forms may be completed even within four generations of multiplication, unless the introgressed segment confers a strong selective advantage (Kopecký et al 2019). In some cultivars, the Festuca chromatin was not detected in any individual analyzed (Kopecký et al 2006).…”

“…Genome stability differs between amphiploid and introgression cultivars of Festulolium (Kopecký et al 2019). 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.…”

Genome Dominance in Allium Hybrids (A. cepa × A. roylei)

“…), chromosomes of Festuca are gradually replaced by those of Lolium (Kopeckyì et al, 2006;Zwierzykowski et al, 2006). In introgression cultivars, complete elimination of Festuca segments is expected to happen within 3-4 generations of multiplication (Kopecký et al, 2019). Therefore, studies on the genome stability of the hybrid genomes and the transmission of the introgressed segment(s) to successive generations may offer some guidance in assessing the potential of the introgression breeding.…”

“…Many traits have been improved via introgression breeding, including resistance to pests and diseases, tolerance to abiotic stresses, and root-related traits ( Anamthawat-Jónsson, 2001 ; Scholten et al, 2007 ; Placido et al, 2013 ; Molnár-Láng, 2015 ). However, introgression lines frequently suffer from the instability of the introgressed segment(s) in the successive generations ( Kopecký et al, 2019 ; Pernickova et al, 2019 ). Combining two genomes in a single nucleus, it opens a way for genome dominance, a phenomenon, when one parental genome becomes dominant, while the other tends to be submissive in a hybrid progeny.…”