Trifolium interspecific hybridisation: widening the white clover gene pool

Abstract

White clover (Trifolium repens) is adapted to moist, fertile soils in temperate zones. Despite its heterozygous allotetraploid nature, it lacks useful genetic variation for survival and growth in semi-arid, infertile soils. Although white clover is apparently genetically isolated in nature, 11 other taxa have so far been found that can be artificially hybridised into the wider gene pool. These species range from annuals to long-lived, hardy perennials with adaptations to stress environments, and they potentially provide new traits for the breeding of more resilient varieties of white clover. The delineation of the secondary, tertiary and quaternary gene pools is described, along with a review of interspecific hybrids achieved to date. The results of large breeding programs to integrate traits from T. nigrescens and 4x T. ambiguum are reviewed, and schemes introduced for the use of T. uniflorum, T. occidentale, T. pallescens, 2x T. ambiguum and 6x T. ambiguum. Interspecific hybrid breeding of white clover has the potential to enable the development of resilient perennial clovers for seasonally dry, infertile grassland environments in many parts of the world.

Achievements and Challenges in Improving Temperate Perennial Forage Legumes

“…Tetraploid T. ambiguum material has been used for introgressing the rhizomatous trait into white clover, producing selection lines with greatly enhanced drought tolerance in comparison with its white clover parent and control varieties (Marshall et al, 2001;Widdup et al, 2003), as well as improved forage quality characteristics (Marshall et al, 2004). The potential of interspecific hybrids between white clover and T. uniflorum to improve drought tolerance has also been carried out (Williams, 2014). Partially fertile backcrosses to T. ambiguum were also reported with different ploidy levels .…”

“…With respect to white clover, several major programs have been undertaken, predominantly in New Zealand and the UK, aimed at introducing important traits into white clover (Williams, 2014). Crosses have been made between white clover and the diploid annual species T. nigrescens (ball clover) (2n = 2x = 16), a profusely flowering species that has high seed yield relative to white clover and good nematode resistance, to introgress cyst nematode resistance (Hussain et al, 1997), root-knot nematode resistance (Pederson and Windham, 1989), and high inflorescence production and seed set into white clover.…”

Caucasian clover (Trifolium ambiguum Bieb.) × white clover (T. repens L.) – interspecific hybrids developed through tissue culture

“…It has been possible to create hybrids indirectly by crossing 6x Caucasian clover with 6x hybrids to produce complex 6x hybrids (Williams et al, 2006b). These were strongly rhizomatous but very low in fertility (Williams et al, 2013) and they have not been further developed (Williams, 2014).…”

“…A range of backcross hybrids, using white clover as the recurrent parent, has been generated and by the third generation of backcrossing, plants that are very similar to white clover but with rhizomes as well as stolon have been produced (Abberton et al, 1998). Little has been reported about hybrids between hexaploid caucasian clover and white clover (Williams, 2014). In this paper, the results of efforts to develop interspecific hybridization between hexaploid Caucasian clover and white clover using tissue culture methods are reported.…”

Forage breeding for changing environments and production systems: an overview

“…For instance in Australia, subterranean clover (Trifolium subterraneum) and phalaris (Phalaris aquatica) are two species that have been the beneficiaries of germplasm introduction and characterisation to greatly extend zones of agronomic adaptation and improve seasonal growth patterns (Oram et al 2009;Nichols et al 2013). At ISFB 2013 this concept was exemplified and extended to the successful incorporation of molecular tools for interspecific hybridisation in white clover and the breeding of the perennial ryegrass/endophyte (Neotyphodium lolii) symbiosis in the plenary presentations by Profs Warren Williams (Williams 2014) and German Spangenberg respectively and in the use of Trifolium arvense genes to develop transgenic white clover with increased condensed tannin production (Hancock et al 2014). These examples of the use of modern tools such as molecular markers, genomic in situ hybridisation and transgenesis are examples of the successful convergence of molecular and classical techniques to solve challenges that have proven to be quite intractable in the past.…”