Seed World

No Need for Luck! Breeding Clover is all Science, Art and a lot of Hard Work

Who knew that the cute clover, so easily found in meadows around the world, can have up to 56 leaflets! At least, this is the current official record of highest number of clover leaflets on a stem, established in 2009. So much for four-leaved clover… Clover, in fact, is the common name for all plants of the genus Trifolium which consists of about 300 species of plants.

Several of them are extensively cultivated as fodder crops, either sown alone or in a mixture with ryegrass. The crop has for a long time formed a staple crop for silaging, because of its versatility. It grows vigorously, shooting up again after repeated mowings; it produces an abundant crop; it is palatable and nutritious for livestock; it fixes nitrogen, reducing the need for synthetic fertilizers; it grows in a great range of soils and climates; and it is appropriate for either pasturage or green composting.

Agronomically, the most important species are red clover (T. pratense), white clover (T. repens); Crimson clover (T. incarnatum); Egyptian clover (T. alexandrinum); clover hybrids and subterranean clover (T. subterraneum).

Clover can be found all over the world, with the highest diversity in the temperate Northern Hemisphere, but many species also exist in South America and Africa, including at high altitudes on mountains in the tropics. They are small annual, biennial, or short-lived perennial herbaceous plants, and can even be evergreen. All the more reason for European Seed to check with some clover breeding companies how much luck is needed to develop a new clover variety. We spoke with Dr David Lloyd, Head of Legume Breeding at IBERS (whose commercial partner is Germinal); Lily Chin, clover breeder at Barenbrug New Zealand; Niels Roulund clover breeder at DLF in Denmark; and Libor Jaluvka, clover breeder at DLF in the Czech Republic.

European Seed (ES): Which clover species is your company mostly focussing on, and for which reason?

Niels Roulund (NR): DLF Seeds is mostly focussing on breeding of white clover (T. repens) and diploid red clover (T. pratense), because these two species have the biggest market potential, fit best to mix with DLF grasses and have the best potential for seed production.

Lily Chin (LC): Clovers are important forage legumes. Grown mainly in a mixture with grass, plantain or chicory, they can contribute significantly to productive pastures, higher animal performance, nitrogen fixation, and improved soil structure. However, until recently some dairy farms do not grow enough clover because the increased use of N fertiliser over the past few decades (in the pursuit of higher milk production) has reduced its performance. With tightening of environmental regulations on N fertiliser levels used on farms, the significance of clovers in pastures has been renewed.

We mostly focus on breeding white (T. repens) and red clovers (T. pratense). White clovers can annually contribute up to 7t dry matter (DM) per hectare and red clovers up to 15 t DM/ha, particularly on farms with inputs of less than 200kg N/ha/year. Our clover breeding program is partly based in New Zealand, where there is also significant clover usage and seed production. Clover lines are sent to multiple locations in Europe for trialling to ensure the clover produced performs under the different soil, climate and farm systems (e.g. dairy farms under mainly cut and carry systems to sheep grazing in the UK). Red clovers have a greater market in Europe than in NZ, due to the cut and carry system on dairy farms in Europa, whereas NZ is practically all grazing.

David Lloyd (DL): Germinal and IBERS focus mainly on breeding red clover and white clover, we also have breeding programmes for hybrids between white clover and related species like Caucasian clover (T. ambiguum).

ES: Are the breeding efforts different for each of these different clover species?

LC: The breeding efforts for white and red clover reflect the market demand.

DL: The bulk of our effort is directed towards our core breeding programmes of conventional red clovers and small, medium and large leafed white clover. We spend roughly equal amounts of time on each, but we have additional programmes devoted to added value traits such as abiotic stress tolerance, nutrient use efficiency and resistance to specific diseases.

Libor Jaluvka (LJ): Our plant breeding in clover is divided into two different programs. The breeding of white clover is located in Denmark and the breeding of red clover is in performed in the Czech Republic. Field plot testing of both species is typically done in Denmark, the Czech Republic, France, England and the US.

ES: Clover is attacked by several fungal diseases, such as Fusarium, Sclerotinia and Anthracnose, and many others. It is well-known, that these diseases cause clover to have a relatively short longevity. Do you breed for ‘persistence’ in your new clover varieties? And how do you go about it?

DL: We also breed for persistency and have made a lot of progress particularly in extending persistency in red clover.  There are a number of factors that contribute to persistency such as disease resistance, winter hardiness and tolerance of grazing.  These all have different genetic bases and require different breeding methodologies.  Mass selection is a very effective technique for “general persistency”.

NR: Yes, in white clover we are artificially inoculating trials with Sclerotinia in order to be able to remove susceptible varieties. In red clover we perform trials which are infected with Anthracnose.

LC: ‘Persistence’ to disease involves many factors in addition to the clovers own genetic potential to be resistant to a strain of disease. The mineral content of soils, crop rotation, and sowing method are some examples that have a bearing on plant health and therefore how well clovers are resistant to disease. Because of this and the importance of also maintaining agronomic traits (yield and flowering), one of the most direct pathways to breed for persistence is by selection of certain populations, particularly in older stands of red clover, when selection pressures are higher.

ES: Clover is often used in mixtures with other grasses. How do you make sure that your new clover varieties can perform well in a mixture with grass species?

LJ: In white clover, most of our breeding trials are done in a mixture of grass and clover. That way, we can select for the white clover lines for the best match with the grass. The red clover breeding is mostly done in pure red clover trials, but the final selections of the best populations are also done in grass-clover mixtures.

LC: All our trials are conducted in grass backgrounds, so these are a test of how well the clover performs in a mixed sward.

DL: We trial all our varieties with companion grasses (typically perennial ryegrass) and monitor the performance and quality of both species over the course of three to four years. We regard the interaction of the two species to be key to the success of a clover variety. A good clover yield is desirable, but it should never be at the expense of its companion grass. Some aggressive clover varieties have the potential to become dominant over the grass, which can be to the detriment to the sward’s overall nutritional balance. We also test our varieties under the conditions for which they are intended, so in the case of white clover we put them through actual animal grazing trials to satisfy ourselves that they will perform well on farm. We believe this is a unique aspect of the Germinal/IBERS clover breeding, selection and testing system.

ES: In most crops earliness is an important breeding goal. How is this in clover? Do you breed for earliness, or rather the opposite?

LC: We call earliness spring yield, and yes, this is one important goal in breeding, in order to match the feed demand and feed supply. However, a line with all-round or multiple stand out seasonal growth is also important.

DL: Earliness has some degree of importance, particularly in red clover. Most of our varieties are early types.

NR: In white clover, we do focus on early spring growth, which is a high priority especially among organic farmers, as many clover varieties start growth a bit later than the grasses. Regarding red clover, we are also focussing more on early material but some of new varieties have a later growth profile.

ES: Protein content and dry-matter yield are also important targets. How easy or difficult is it to increase these levels?

DL: Like all traits, achieving success in dry-matter yield and/or protein content is a question of effort and resources. Dry-matter yield is a simple measure and is typically the most important trait by which potential varieties are assessed. Protein content is more complicated to select for but as long as you have heritable variation you can breed for increased protein content.

LJ: Protein content can be increased relatively easy, however, the primary breeding target is dry-matter yield – which is more difficult to increase.

ES: What other breeding targets do you spend your resources on for clover in Europe?

NR: The seed yield of new varieties must be sufficient to ensure, that seed production can be done in an economically sustainable way – so we invest quite a lot in seed yield trials.

LC: Yield, persistence and seed production are the core traits in the breeding program. For the red clovers, habit is also important as it is used for hay/silage and needs to grow with tall fescue or ryegrass in mixed pasture systems.

For simplicity, white clover is divided into three different types, based on leaf size (large, medium and small) to help determine which clover types or clover mixes are best suited for the farm system. For example, large and medium types are more oriented towards a cut and carry system for dairy grazing in the majority of Europe, whereas medium to small leaf types that have greater stolon growing point densities, and are more suited to sheep grazing in the UK.

DL: Aside from yield and persistency we breed for disease and pest resistance, abiotic stress tolerance and nutrient use efficiency. We have developed hybrids of white and Caucasian clover, such as the variety ‘AberLasting’, that have remarkable drought tolerance, cold tolerance, grazing tolerance and pest resistance. We believe this variety has the potential to make a major difference to grassland agriculture, particularly in areas where white clover struggles to persist. We are also developing grazing tolerant varieties of red clover, which is a very exciting step forward.

ES: Creating diversity for your growers and customers is of crucial importance for any breeder. Where do you go to find the necessary germplasm that will help you in your breeding work? What are the main source of your diversity: mainly commercial varieties, or also landraces and other species?

LC: Our germplasm originates from a range of sources: local and global plant collections from both temperate and continental climates, developing our own germplasm through our crossing program, elite lines and commercial lines. Much of the global plant collections are accessed from germplasm banks.

DL: We generally use population based breeding methodologies for our core breeding programmes but we also utilise commercial varieties, land races and eco types to source novel variation

LJ: The main source for diversity in white- and red clover is commercial varieties, in-house breeding material and collected material from nature. Creating diversity for your growers and customers is of crucial importance for any breeder.

ES: Do you find that you have sufficient access to new germplasm, or has this been made more difficult because of the new regulations on access and benefit sharing?

DL: We have an extensive gene bank of tens of thousands of accessions that have been collected from around the world over the last hundred years. Breeding began at the Welsh Plant Breeding Station in Aberystwyth in 1919, we will celebrate our centenary next year. If anything, our problem is finding time to assess the material we already have!

NR: As long as the present UPOV rules not are changed, we have no problems.

ES: Which kind of investments in time & money (on average and rough estimates) does it take to develop a new clover variety?

LJ: Breeding clovers is a slow process. To create a new variety from scratch takes around 14 years, including 3-4 years of registration in official trials.

LC: Each clover line takes 11 years to develop. As the clovers we breed are bee-pollinated, spreading plants that produce hard seeds (particularly white clovers), investments in a range of pollination cages, short and long tongue bumble bees, and specialised field equipment are necessary.

DL: It takes roughly 15 years from initial crosses to produce a new variety that can be marketed. The financial cost of this can vary but it is substantial.

ES: How does your organization make sure that your future products are aligned with what the growers want?

LC: We have field agronomists, sales, and seed production teams who interact with growers, farmers and re-sellers. They are also encouraged to visit our research station, so there is a flow of information and ideas in both directions.

DL: The Breeding Team at IBERS works closely with our commercial partner Germinal to ensure understanding of on farm requirements from the UK, Ireland, New Zealand and further afield. It is vital for the breeding programme that the varieties produced are commercially beneficial for the farmer and make a difference to financial performance of farms, whether domestically or overseas.

NR: We are having annual meetings with our product managers. The product managers are present in many countries and are working directly with farmers. They know the demand for future traits and it is valuable information for the plant breeders.

ES: What is the biggest challenge for a breeder when developing a new clover variety?

DL: Breeding is a long process. It can be difficult to judge what the market will need in 20 or 30 years that will suit the requirements of a changing market. IBERS therefore works closely with Germinal to ensure that possible future trends are identified and addressed within the breeding programme.

LJ: To combine a high dry matter yield with a high seed yield – and to foresee new demands and developments.

LC: Agronomic traits of clover and many plants are on the opposite ends of the pendulum. Flowering and persistence for example are on opposite ends to the yield trait. Whilst breeding can push these traits closer, it is a slow process as obtaining the extremes of these agronomic traits is against the natural pendulum.

ES: What are the innovations (technological, genetic, molecular etc.) which are in the pipeline in clover breeding?

NR: Genome Wide Selection will the next technology added to the clover breeding.
LC: In recent years, genomic selection and hybrid breeding research have come into the clover breeding pipeline helping accelerate traditional phenotypic based clover breeding and screen the diverse genetics available in other white clover species.

DL: Plant breeding is at the beginning of a new era with the advent of genomic selection. This will give us the ability to assess the overall breeding value of individual plants on the basis of their genetic sequence without having to assess them in the field and measuring different traits over several seasons. This will allow us to look at more material, improve the efficiency of selection and speed up the overall breeding process, resulting in better varieties coming to market far more quickly than they currently do.