It’s back to the future for white clover

The white clover that has helped the New Zealand pastoral sector thrive has had its interesting history unearthed by AgResearch scientists.

Recent research shows that the popular legume, Trifolium repens, most likely came about through the meeting of two plants from very different environments.

This knowledge enables researchers to look for closely related plants they can use to create new hybrids to meet the challenges of changing farming conditions.

Work led by Dr Warren Williams at AgResearch in Palmerston North has confirmed the hypothesis that T. repens was most likely created from the crossing of Trifolium pallescens, an alpine species and Trifolium occidentale, a coastal species.

“White clover is a ubiquitous weed of the temperate world that through use of improved cultivars has also become the most important legume of grazed pastures world-wide, but its ancestral species have remained elusive” he says.

“Evidence from DNA sequence analyses, molecular cytogenetics, interspecific hybridisation and breeding experiments supports the hypothesis that an alpine species hybridised with a coastal species to generate tetraploid T. repens.

“The coming together of these two narrowly adapted species (one alpine and the other coastal), along with allotetraploidy, has led to a transgressive hybrid with a broad adaptive range.

“Glacial movements in an ice-age thousands of years ago forced T. pallescens to lower altitude refuges, where T. occidentale was also present. The coming together of these two species led to a hybrid with a broad adaptive range – white clover.”

While white clover is adapted to moist, fertile soils in temperate zones, it lacks useful genetic variation for survival and growth in semi-arid, infertile soils.

Eleven other species have now been identified that can be artificially hybridised into the white clover gene pool.

These range from annuals to long-lived, hardy perennials with adaptations to stress environments. They potentially provide new traits for the breeding of more resilient varieties of white clover.

“Hybrid breeding of white clover has potential for development of resilient perennial clovers for seasonally dry, infertile grassland environments in many parts of the world,” says Dr Williams.

“For example a hybrid of T. repens and T. uniflorum (from arid Greece) creates: T. repens × T. uniflorum which has shown improved drought resistance, and better tolerance of low soil phosphate.”

This work will help to maintain white clover’s role as the plant many consider to be New Zealand’s natural advantage, no matter what future challenges it faces.