Androgenesis from Festuca pratensis x Lolium multiflorum amphidiploid cultivars in order to select and stabilize rare gene combinations for grass breeding

Species with Haploid or Doubled Haploid Protocols

In this chapter, we present a list of species (and few interspecific hybrids) where haploids and/or doubled haploids have been published, including the method by which they were obtained and the corresponding references. This list is an update of the compilation work of Maluszynski et al. published in 2003, including new species for which protocols were not available at that time, and also novel methodologies developed during these years. The list includes 383 different backgrounds. In this book, we present full protocols to produce DHs in 43 of the species included in this list. In addition, this book includes a chapter for one species not included in the list. This makes a total of 384 species where haploids and/or DHs have been reported up to date.

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

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.

Cytogenetics of Festulolium (Festuca x Lolium hybrids)

Grasses are the most important and widely cultivated crops. Among them, ryegrasses (Lolium spp.) and fescues (Festuca spp.) provide high quality fodder for livestock, are used for turf and amenity purposes, and play a fundamental role in environment protection. Species from the two genera display complementary agronomic characteristics and are often grown in mixtures. Breeding efforts to combine desired features in single entities culminated with the production of Festuca x Lolium hybrids. The so called Festuloliums enjoy a considerable commercial success with numerous cultivars registered all over the world. They are also very intriguing from a strictly cytogenetic point of view as the parental chromosomes recombine freely in hybrids. Until a decade ago this phenomenon was only known in general quantitative terms. The introduction of molecular cytogenetic tools such as FISH and GISH permitted detailed studies of intergeneric chromosome recombination and karyotyping of Festulolium cultivars. These tools were also invaluable in revealing the origin of polyploid fescues, and facilitated the development of chromosome substitution and introgression lines and physical mapping of traits of interest. Further progress in this area will require the development of a larger set of cytogenetic markers and high-resolution cytogenetic maps. It is expected that the Lolium-Festuca complex will continue providing opportunities for breeding superior grass cultivars and the complex will remain an attractive platform for fundamental research of the early steps of hybrid speciation and interaction of parental genomes, as well as the processes of chromosome pairing, elimination and recombination.

Genome balance in six successive generations of the allotetraploid Festuca pratensis x Lolium perenne

In the allotetraploid, Festuca pratensis Huds. (2n = 4x = 28) x Lolium perenne L. (2n = 4x = 28) the balance of chromatin, as determined by GISH, changes over successive generations of open pollination in favour of L. perenne. There is extensive recombination between chromosomes of the two parental genomes, as well as substitution of whole Festuca chromosomes by whole Lolium chromosomes. The total number of Lolium chromosomes increased from a mean 14.36 in the F(2) to 16.26 in the F(6), and the total number of Festuca chromosomes decreased correspondingly from a mean of 13.57 to a value of 11.56. The number of recombinant chromosomes and recombination breakpoints per genotype also increased from generation to generation, although the respective values of both characters were higher for Festuca (0.86-8.41 and 1.14-15.22) than for Lolium (0.68-4.59 and 0.68-6.0). The proportion of total genome length contributed by the L. perenne chromatin increased from about 50% in F(2) to 59.5% in F(6). The results are based on the sample of 134 plants studied (26-28 plants per generation), and are discussed in terms of the dominance of Lolium chromosomes over those of Festuca, and possible mechanisms underlying this phenomenon of chromatin substitution.

GISH/FISH mapping of genes for freezing tolerance transferred from Festuca pratensis to Lolium multiflorum

The first backcross breeding programme for the transfer of freezing-tolerance genes from winter hardy Festuca pratensis to winter-sensitive Lolium multiflorum is described. A partly fertile, triploid F(1) hybrid F. pratensis (2n=2x=14) x L. multiflorum (2n=4x=28) was employed initially, and after two backcrosses to L. multiflorum (2x) a total of 242 backcross two (BC(2)) plants were generated. Genomic in situ hybridisation (GISH) was performed on 61 BC(2) plants selected for their good growth and winter survival characters in the spring following one Polish winter (2000-2001). Among the winter survivors, diploid chromosome numbers were present in 80% of plants. An appropriate single Festuca introgression in an otherwise undisturbed Lolium genome could provide increased freezing tolerance without compromise to the good growth and plant vigour found in Lolium. Among all the diploids, a total of 20 individuals were identified, each with a single F. pratensis chromosome segment. Another diploid plant contained 13 Lolium chromosomes and a large metacentric F. pratensis chromosome, identified as chromosome 4, with two large distal Lolium introgressions on each chromosome arm. Three of the diploid BC(2), including the genotype with Festuca chromosome 4 DNA sequences, were found to have freezing tolerance in excess of that of L. multiflorum, and in one case in excess of the F. pratensis used as control. A detailed cytological analysis combining GISH and fluorescence in situ hybridisation analyses with rDNA probes revealed that the other two freezing-tolerant genotypes carried a Festuca chromosome segment at the same terminal location on the non-satellite arm of Lolium chromosome 2.

Genetic characterization of androgenic progeny derived from Lolium perenne x Festuca pratensis cultivars

Androgenesis and genetic characterization of androgenic progeny from Lolium perenne x Festuca pratensis cultivars (2n = 4x = 28) were investigated in order to develop a novel grass that combines favourable attributes of parent plants. A successful androgenesis was obtained using PG-96 medium. The green plant regeneration was 46%, 35% and 17% for Bx350, Bx351 and Prior, respectively, and over 800 green plants have been obtained. Androgenic progeny showed a large variation in freezing tolerance, 7% of 292 progeny exceeding that of freezing hardy F. pratensis despite containing chromosomes of L. perenne. More than 60% of 175 flowering progeny produced dehiscent anthers with pollens. Androgenic plants contained 14 or 28 chromosomes. There were 188 (56%), 204 (77%) and 114 (81%) dihaploids from Bx350, Bx351 and Prior, respectively. The nuclear DNA content varied significantly even between plants with the same chromosome number. High levels of chromosome pairing and recombination were observed by genomic in situ hybridization analysis because of close homology between two genomes. The results indicated that androgenic progeny of Festulolium showed high level of genetic variation, and provide potential for accelerating selection efficiency.

A decade of “chromosome painting” in Lolium and Festuca

GISH has been a particularly useful technique for studying the Lolium-Festuca species complex of forage grasses. The reason for this utility is two-fold: (i) the complex is unique amongst crop plants in which fertile hybrids, and backcross progenies, can be produced which recombine genomes and promiscuously exchange their genes through homoeologous recombination; (ii) dispersed repetitive DNAs differ between species, and this allows tracking of the identity of chromosomes and chromosome segments. This tracking property has enabled several fruitful lines of research to produce a harvest of new information for both fundamental and practical purposes. We review this first decade of GISH (genomic in situ hybridization) in Lolium-Festuca, and discuss and summarize the achievements which have accrued.