Thursday, July 7, 2022

The king of clover

From his chair at AgResearch Grasslands, Dr Warren Williams can look far back into the origins of white clover and forward to clover hybrids, which he says will revitalise pastoral farming.

“White clover has been called the linchpin of New Zealand agriculture,” Warren said, in an analogy that makes him and his colleagues mechanics of the rural economy.

That rural economy is based on introduced pasture plants, which is why we need a centre for research excellence like Grasslands.

Warren, a lifelong NZ plant breeder specialising in enhancement of genetic resources of grassland plants, has high hopes for more pasture persistence, animal nutrition and pest resistance in the commercially available clovers of the near future.

His official titles are plant germplasm specialist for AgResearch Grasslands and AgResearch Professorial Fellow in Plant Breeding, Massey University.

In the eight years Warren’s team has been delving into interspecific hybridisation among clovers it has discovered the ancestors of white clover, revolutionised clover taxonomy and made a good start on several promising hybrids for the benefit of farmers.

In another six to eight years enhanced clover hybrids will be available for farms, he said.

Publication in the journal BMC Plant Biology during the year was a first for Warren and his co-authors, alerting the rest of the world to their white clover breakthrough.

Warren was also keen to mention colleague Zane Webber, intrepid seed collector worldwide and manager of the Margo Forde Forage Germplasm Centre in Palmerston North, which contains a rich resource of 200 clover species from which the hybrid breeders draw.

While white clover (Trifolium repens) is the most important legume in grazed pastures around the world it has some drawbacks, which have been painfully obvious throughout NZ in recent times.

“Farmers believe their clovers and grasses are not lasting as long and they are asking why,” Warren said.

Clover content in pastures in northern regions has dropped dramatically under attack from weevils.

Droughts and hot summers tend to take out white clover plants, as does pugging damage in the winter.

“Better stress tolerance is therefore our number one objective in the clover breeding programme,” Warren said.

The revitalisation of clover in our pastures, with its nitrogen-fixing role and higher animal nutrition, should also help the more sustainable drive in agriculture, particularly dairying, towards lower inputs and higher outputs.

“I can see our clover legacy coming back into prominence in a few years,” he said.

Warren’s DNA detectives discovered that a diploid alpine clover species (T. pallescens) hybridised with a diploid coastal species (T. occidentale) to generate allotetraploid Trefolium repens.

The coming together of these two narrowly adapted species, one alpine and the other maritime, thousands of years ago led to the widely spread hybrid clovers we know today.

Now they can go back to the antecedents and “synthesise” white clover and increase the most desirable traits like drought resistance and tolerance to lower soil phosphate.

Warren’s wife Isabelle Verry does much of the fiddly work of cross-pollination and embryo rescue and others take over the painstaking work of getting fertile seeds from the hybrids and making reproducing populations so that trait evaluation can begin.

“We have a team now united behind a common interest of making these crosses to improve clovers,” Warren said.

As with all plant breeding, thousands of crosses must be done to find one hybrid with exciting promise, which must then be trialled and measured for years before commercialisation.

“But from DNA to farm use in perhaps 15 years is really good progress,” Warren said.

The contribution of plant breeders to the national economy goes largely untold but farmers should value their work with the building blocks of life.

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