Development of Genomic Resources in the Species of Trifolium L. and Its Application in Forage Legume Breeding

Abstract

Clovers (genus Trifolium) are a large and widespread genus of legumes. A number of clovers are of agricultural importance as forage crops in grassland agriculture, particularly temperate areas. White clover (Trifolium repens L.) is used in grazed pasture and red clover (T. pratense L.) is widely cut and conserved as a winter feed. For the diploid red clover, genetic and genomic tools and resources have developed rapidly over the last five years including genetic and physical maps, BAC (bacterial artificial chromosome) end sequence and transcriptome sequence information. This has paved the way for the use of genome wide selection and high throughput phenotyping in germplasm development. For the allotetraploid white clover progress has been slower although marker assisted selection is in use and relatively robust genetic maps and QTL (quantitative trait locus) information now exist. For both species the sequencing of the model legume Medicago truncatula gene space is an important development to aid genomic, biological and evolutionary studies. The first genetic maps of another species, subterranean clover (Trifolium subterraneum L.) have also been published and its comparative genomics with red clover and M. truncatula conducted. Next generation sequencing brings the potential to revolutionize clover genomics, but international consortia and effective use of germplasm, novel population structures and phenomics will be required to carry out effective translation into breeding. Another avenue for clover genomic and genetic improvement is interspecific hybridization. This approach has considerable potential with regard to crop improvement but also opens windows of opportunity for studies of biological and evolutionary processes.

Achievements and Challenges in Improving Temperate Perennial Forage Legumes

“…The genetic resources in Trifolium, and their utilization in plant breeding of red and white clover and other clover species, has been the subject of several recent reviews (Abberton and TABLE 3 The species closely related to white clover (section Trifoliastrum), after Williams and Nichols (2011) Species Ploidy Annual/perennial Abberton and Thomas, 2011;Ravagnani et al, 2012). White clover exhibits considerable adaptive variation between populations (Williams, 1987a), along with high levels of phenotypic plasticity and intra-population variation.…”

“…The phylogenetic relationship between red clover and related species is not as clear as for white clover (Ravagnani et al, 2012). Most studies are based on cross-compatibility and chromosome pairing in hybrids, but a complication is represented by the fact that red clover is the only species with n = 7 amongst its closest relatives in the section Trifolium (Ellison et al, 2006).…”

“…T. occidentale has been developed as a model species for genetic and genomic research relating to the white clover complex (Williams et al, 2009). The potential role of interspecific hybridization using these wild relatives in the genetic improvement of white clover has been discussed by Abberton and Marshall (2005) and Ravagnani et al (2012).…”

Legume Crops Phylogeny and Genetic Diversity for Science and Breeding

“…Generation of segregating progenies from these crosses would enable mapping of these traits and the discovery of the hidden genes. This could have dramatic consequences on clover breeding programs (Ravagnani et al, 2012).…”

“…By the end of the seventeenth century, clover cultivation had spread over most of Europe, reaching the northern areas by the end of the eighteenth century (Kjaergaard, 2003). Cultivated clovers generally have larger leaves and flower earlier and more prolifically than their wild ancestors or relatives (Ravagnani et al, 2012).…”