Huw M. Thomas

Discriminating the ancestral progenitors of hexaploid Festuca arundinacea using genomic in situ hybridization

The phylogeny of Festuca arundinacea Schreb. (2n = 6x = 42) was determined using GISH. Total genomic DNA of putative ancestral species was labelled with rhodamine and hybridized to chromosome preparations of hybrids involving these species and F. arundinacea. The degree of hybridization to chromosomes known to be homologous to the probe DNA was compared with that found simultaneously on chromosomes of the genome of F. arundinacea. It was concluded that the tetraploid species Festuca arundinacea var. glaucescens contributed two genomes and the diploid species Festuca pratensis one, to create the allohexaploid species F. arundinacea.

Introgression mapping in the grasses. I. Introgression of Festuca pratensis chromosomes and chromosome segments into Lolium perenne

Lolium perenne (4x)/ Festuca pratensis (2x) triploid hybrids (2n=3x=21) were produced and backcrossed to Lolium perenne. The BC1 progeny, which predominantly had 14 chromosomes, were analysed using genomic in situ hybridization (GISH) and genetic markers. GISH revealed that over 74% of the BC1 individuals carried one or more F. pratensis chromosome segments. By comparing the physical size of introgressed F. pratensis chromosome segments with the presence or absence of F. pratensis-specific polymorphisms, it was possible to determine the physical position of genetic markers. The potential of a new type of genetic mapping (‘introgression mapping’) for the alignment of physical and genetic maps, determining the genetic control of agronomically important characters and the production of novel germplasm for the development of new varieties is discussed.

Gross chromosome rearrangements are occurring in an accession of the grass Lolium rigidum.

Chromosome structure was analysed at mitosis in root tip meristems of eight genotypes of Lolium rigidum. FISH revealed changed positions in the rDNA sites indicating extensive chromosome rearrangements; indeed no two genotypes were the same. In one genotype, there were differences between cells within individual root tips. The changed positions of the rDNA sites appear to be reflections of chromosome translocations and this was confirmed by the presence of quadrivalents at metaphase I of meiosis. Possible mechanisms are discussed for this exceptional level of chromosome instability.

Molecular Breeding and Functional Genomics for Tolerance to Abiotic Stress

Sustainability is a measure of our ability to produce food with the maximium of efficiency combined with the minimum of damage to the environment. Grasslands represent over 40% of all agricultural land in the European Union, and over 70% in the United Kingdom. Whilst Lolium in Europe is considered to be the ideal source of profitable and safe high quality animal forage, its general poor persistency limits its use to favourable growing areas. Fortunately, genes for abiotic stress resistance are transferred readily from closely related Festuca species by conventional breeding technologies. Introgression mapping allows the assembly of desirable gene combinations and molecular markers to assist with their selection in breeding programmes. Additional new androgenesis techniques have led to novel genotypes rarely observed as outcomes of breeding programmes. Lolium × Festuca hybrids display promiscuous chromosome recombination enabling genes from one species to be transferred readily to homoeologous chromosome regions where they both function normally and remain stable. Despite the close homology between Lolium and Festuca species, repetitive DNA sequences differ sufficiently for their genomes to be distinguished, by genomic in situ hybridisation (GISH). This enables the physical mapping of genes for abiotic stress resistance transferred from Festuca to Lolium. Further chromosome recombination between homoeologous Lolium and Festuca sequences enables Festuca introgressions to be “dissected”, and recombination series created. Knowledge of synteny and gene sequences within model species amongst the Poaceae, combined with the development of sequenced molecular markers, and bacterial artificial chromosomes is enabling the isolation of genes for abiotic stress resistance.

Labelling telomeres of cereals, grasses and clover by primedin situ DNA labelling

Primedin situ DNA labelling (PRINS) labels the telomeres ofAvena, Triticum, Secale, Hordeum, Lolium, Festuca andTrifolium when primers are used that correspond to the repeat unit ofArabidopsis telomeres. There are interstitial sites labelled in aLolium x Festuca hybrid.

Chromosome pairing in Lolium perenne · L. temulentum diploid hybrids: genetic and cytogenetic evaluation

A Lolium perenne genotype (E5/2/5/10), which had been selected for low chiasma frequency over a number of generations and which was suspected of containing one or two heterozygous dominant genes with a significant effect on chiasma frequency, was crossed with L. temulentum (Ba3081) to create a hybrid population of 47 diploid plants. The mean chiasma or paired arm (PA) frequency of homoeologous chromosomes at meiosis in the population was 9.1/cell (1.3 PA/chromosome pair) with a distribution skewed towards high PA frequency. More than 90% of the hybrid chromosomes paired at meiosis in spite of the disparity in chromosome length and DNA quantity between the two species. Overall, the distribution of PAs between chromosomes for a given number of PAs/cell favoured the production of rod bivalents over ring bivalents and univalents, indicating that there is a mechanism present that maximizes the total number of bivalent associations formed. Molecular marker analysis using AFLPs and isoenzymes did not identify any clear major gene effect on PA frequency in the hybrid population. It was concluded that the control of PA frequency in E5/2/5/10 was not a simple genetic mechanism.