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

Abstract

Lolium perenne (4x)/Festuca pratensis (2x) triploid hybrids (2n = 3x = 21) were produced and backcrossed to Lolium perenne. The BC 1 progeny, which predominantly had 14 chromosomes, were analysed using genomic in situ hybridization (GISH) and genetic markers. GISH revealed that over 74% of the BC 1 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.Keywords: genetic mapping, genomic in situ hybridization, introgression mapping, physical mapping, recombination. IntroductionGenome mapping is a powerful approach to the study of plant biology, facilitating the location of genes responsible for agronomically and scientifically important traits. Phenotype mapping is the primary justification for the development of genetic maps. DNA markers closely linked to a gene responsible for a desirable phenotype are an important tool for indirect selection in breeding programmes and in addition provide a springboard from which genes can be isolated via map-based cloning. To increase the efficiency of mapping, parental genotypes which exhibit high DNA marker allele diversity are chosen. The genetic base of many crop species, however, is narrow, but this problem can be overcome by generating maps from wide crosses.The forage grass Lolium perenne (Lp) (2n = 2x = 14) can be readily hybridized with Festuca pratensis (Fp) (2n = 2x = 14) to form a 14-chromosome hybrid which exhibits full pairing at metaphase I of meiosis (Lewis, 1966;Jauhar, 1975). These diploid hybrids show nearly complete sterility (Lewis, 1966;Jauhar, 1975). However, LpLpFp triploids, derived by hybridizing synthetic tetraploid L. perenne with diploid F. pratensis, show both male and female fertility (Jauhar, 1975). The ease of hybridization, the chromosome pairing observed at meiosis and a preliminary molecular genetic study on the phylogeny of these species (Stammers et al., 1995) indicate that they are closely related. In contrast, the sterility of the diploid hybrid, the ease with which Lp and Fp chromosomes can be distinguished using genomic in situ hybridization (GISH) , and the position and number of rDNA sites in the two species (Thomas et al., 1996; indicates that they are distantly related. Thus the phylogenetic relationship between Lp and Fp at present remains a paradox.The work presented in this paper describes a new kind of genetic mapping in the grasses. 'Introgression mapping' is based on the ability to distinguish *Correspondence. E-mail: ian.king@bbsrc.ac.uk ©1998 The Genetical Society of Great Britain. 462Lp and Fp chromosomes and chromosome se...

Introgression of crown rust (Puccinia coronata) resistance from meadow fescue (Festuca pratensis) into Italian ryegrass (Lolium multiflorum) and physical mapping of the locus

“…In this case, triploid F 1 hybrids were produced using a crown rust-susceptible tetraploid genotype of Lm (2n ¼ 4x ¼ 28) as the female parent, and a resistant Fp as the pollen donor. Tetraploid Lm was used as this has been proven to be the most efficient route to obtain introgression (King et al, 1998;Thomas et al, 1988). For the first backcross generation, the triploid F 1 hybrids (2n ¼ 3x ¼ 21) were used as both the male and female parent, since some were male sterile or had low male fertility.…”

“…Excised root tips were kept in icecold water either for 16 h (for mitotic cell divisions) or 18 h (for in situ hybridisation) and then fixed in ethanol:acetic acid (3:1) for a minimum of 2 h. For chromosome counts, root tips were stained by the Feulgen method and squashed on a microscope slide in 1% acetocarmine. For in situ hybridisation, metaphase spreads were treated by the procedure described by Thomas et al (1994) and King et al (1998). Total genomic Fp DNA was used as a probe to detect Fp introgressions; this was labelled either with Cy3-dCTP (Amersham Pharmacia Biotech, UK) (red) or dig-11-dUTP (Boehringer Mannheim, UK) and detected by the fluorescein detection procedure (green).…”

“…On the other hand, the relationship is sufficiently distant that L. multiflorum (Lm) and F. pratensis (Fp) chromosomes can be distinguished in hybrid plants using genomic in situ hybridisation (GISH) (Thomas et al, 1994). The potential use of Lolium/Festuca introgression mapping to develop physical and genetic maps, determine the genetic control of important characters and develop new germplasm for plant breeders has been discussed previously (King et al, 1998). Using this technique, it has been possible to identify a segment of chromosome from F. arundinacea introgressed into Lm and carrying drought tolerance (Humphreys and Pasakinskiene, 1996).…”

Stability across environments of the coffee variety near infrared spectral signature

“…Molecular markers are widely used to study alien gene introgression in a large number of crop species (Fulton et al, 1997;King et al, 1998). In coffee, amplified fragment length polymorphism and simple sequence repeats have been successfully used to analyze the introgression of DNA fragments from Coffea canephora and Coffea liberica into C. arabica (Lashermes et al, 2000;Prakash et al, 2002;Herrera et al, 2002a).…”

Introgression mapping in the grasses. II. Meiotic analysis of the Lolium perenne/Festuca pratensis triploid hybrid

“…Lolium perenne/Lolium perenne/Festuca pratensis (LpLpFp) triploid hybrids are a potentially important source of material for determining the genetic control of agronomically and scientifically important characters and in assessing the relationship of physical and genetic maps (King et al, 1997(King et al, , 1998 (Lewis, 1966;Jauhar, 1975). However, LpLpFp triploids, derived by hybridizing synthetic tetraploid L. perenne with diploid F. pratensis, frequently show both male and female fertility (Jauhar, 1975).…”