Introgression-mapping of genes for drought resistance transferred from Festuca arundinacea var. glaucescens into Lolium multiflorum

Abstract

Procedures for the transfer of genes for drought resistance from Festuca glaucescens (2n=4x=28) into Lolium multiflorum (2n=2x=14) are described. Following the initial hybridisation of a synthetic autotetraploid of L. multiflorum (2n=4x=28) with F. glaucescens, the F1 hybrid was backcrossed twice onto diploid L. multiflorum (2n=2x=14) to produce a diploid Lolium genotype with a single F. glaucescens introgression located distally on the nucleolar organiser region arm of chromosome 3. The transmission of F. glaucescens-derived amplified fragment length polymorphisms and a sequence-tagged-site (STS) marker was monitored throughout the breeding programme. Those genotypes of a mapping population of backcross 3 that survived combined severe drought and heat stress all contained the F. glaucescens-derived markers. The STS marker provided a prototype for a PCR-based system for high-throughput screening during cultivar development for the presence of the F. glaucescens-derived genes for drought resistance. The frequency of intergeneric recombination between L. multiflorum and F. glaucescens is described. During the initial stages of the breeding programme, preferential intraspecific chromosome pairing between Lolium homologues and Festuca homoeologues dominated with low frequencies of intergeneric chromosome associations. However, these increased in the backcross 1 due to the absence of opportunities for intraspecific chromosome pairing between homoeologous Festuca chromosomes following the loss of half of the Festuca chromosomes. Once transferred to Lolium, F. glaucescens sequences recombined with Lolium at high frequencies, thereby enabling the loss of potentially deleterious gene combinations that might reduce the forage quality of Lolium.

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

“…However, the significance of the Fp introgressions reported here is greater, as Lm is more sensitive to freezing conditions than L. perenne and the benefits to accrue from the Fp introgressions reported herein are therefore more significant. Despite freezing tolerance being a quantitative character governed by many genes, it is demonstrated here, as was reported previously for drought resistance (Humphreys and Pašakinskienė , 1996;Humphreys et al, 2005), that a single Festuca introgression can make a significant impact on the resistance of Lolium against abiotic stresses.…”

“…For example, in diploid L. multiflorum introgression forms obtained from the backcrossing of L. multiflorum (4x) Â F. glaucescens (4x) hybrid, a Festuca introgressed segment with genes governing drought resistance has been located on the NOR arm of Lolium chromosome 3 (Humphreys et al, 2005). In this study, clones of pTa/71 containing a fragment of 18S-5.8S-26S rDNA from Triticum aestivum and pTa794 (with a fragment of 5S rDNA from T. aestivum) were used for chromosome identification.…”

“…Furthermore, a shift towards the Lolium parental genotype in amphiploid L. perenne or L. multiflorum  F. pratensis over several generations (up to F 8 ) has been observed by different research groups (Zwierzykowski et al, 1998(Zwierzykowski et al, , 2003Canter et al, 1999;Pašakinskienė and Jones, 2003). As recombination between homoeologous Lolium and Festuca chromosomes occurs frequently in hybrids, opportunities for gene introgression arise, enabling the transfer to Lolium of Festuca genes for improved persistency, through a backcross breeding programme (Thomas et al, 1994Humphreys et al, 1997Humphreys et al, , 2003Humphreys et al, , 2005King et al, 1998;Zwierzykowski et al, 1998Zwierzykowski et al, , 1999. The targeted inclusion of desirable Festuca gene combinations can be accompanied by the targeted exclusion of other Festuca genes considered detrimental to the high forage quality traits found in Lolium.…”

Root imaging showing comparisons in root distribution and ontogeny in novel Festulolium populations and closely related perennial ryegrass varieties

“…In Bx510, the translocated fescue introgression derived from F. arundinacea var glaucescens and located at a terminal position on the satellite region of chromosome 3 of Lolium (Humphreys et al, 2005). Its role in improving water-use efficiency may well differ from those in Bx509.…”

An Increasing Need for Productive and Stress Resilient Festulolium Amphiploids: What Can Be Learnt from the Stable Genomic Composition of Festuca pratensis subsp. apennina (De Not.) Hegi?

“…From a plant breeding perspective, any prolonged cessation in foliar growth is far from ideal from the perspective of satisfying requirements for achieving sustainable agricultural production and sufficient fodder provision for livestock. However, the incorporation of genes for drought and heat tolerance from F. glaucescens into Lolium has been achieved without recourse to summer growth cessation (Humphreys et al, 2005) showing that drought avoidance alone is not the only strategy available to F. glaucescens to combat drought stresses. As it shares common ancestral genomes, the findings by Humphreys et al (2005) provide hope that equivalent physiological mechanisms for stress-tolerance may be available to F. apennina that may provide benefits to Lolium spp.…”