Created on the basis of: Verdaguer B., Bonnecuelle M.H., Balardelle C., Romestant M., Lacaze P. (2005). Génie génétique appliqué à l’amélioration des espèces fourragères. Fourrages, 183, 347-364.
Principles and Objectives
The global human population is constantly growing and will reach nearly eight billion people in next few years, and has many mouths to feed. While a significant part of our diet consists of milk and meat produced by farming, the area of grasslands used to feed these farm animals appears to be a limited resource. If it is necessary to feed increasing numbers of people with an allocated surface which does not increase, it is necessary to increase one way or another the performance of these surfaces.
Genetic research is one of the ways to achieve this. It is possible to improve the characteristics of a plant by isolating specific genes that have particular specificities (disease resistance, drought tolerance, hypolignification, etc.), by extracting a host genome (from plants, bacteria, fungi, etc. ), then reintroducing them into the genome of a plant species. These organisms are genetically modified: we are talking about GMOs.
Until the early 2000, these GMOs relate mainly to two bacterial genes, increasing resistance either to a herbicide, or to certain insects. Since then, numerous other possibilities have been explored attempting to (genetically) improve feed varieties. One of the necessary and essential processes consists of deciphering the genomes of plant species (as was the case with rice, Medicago truncatula, and then later with perennial ryegrass, Timothy, etc.), which allows for the isolation of new genes and the better understanding of the genomic structure of the species likely to be improved.
It is important to underline that techniques used to obtain plants’ GMO are the same as for animals’ GMO; some of their applications are used in our everyday lives. For example, the insulin manufactured to treat diabetes is the result of a bacterial GMO (E. coli).
There are actually two ways to improve a variety: by continually improving its strengths or by reducing its weaknesses. Both routes involve many aspects, of quantitative nature (content of lignin, content of protein, etc..) or qualitative nature (adaptability, quality, strength, tolerance, etc.).
Historically, herbicide-resistant GMOs were among the first to be developed, and were also the first on the market.
In terms of performance, it is helpful for a farmer to eliminate weeds present in grassland (or in the cereal field). To do so, he uses one or more selective herbicides capable of removing unwanted weeds and leaving cultivated plants more or less intact. But this technique is dangerously polluting, residual (herbicide remaining in the soil long after its use (and therefore more polluting)), expensive, time consuming as the herbicide should be applied at a specific period of development of the plant, etc.
In the mean time, we know of a molecule capable of inhibiting an enzyme (EPSPS) responsible for the synthesis of aromatic amino acids necessary for the development of plants: glyphosate (commercially known as Roundup®). In contact with a plant, glyphosate permanently stops its growth (and therefore leads to its death).
In 1990, it is shown that plants with overexpression of one EPSPS gene are significantly resistant to the glyphosate. Four years later, after having introduced the gene of the EPSPS enzyme of a bacterial strain (Agrobacterium) into varieties of soybean, the Monsanto company announces obtaining the first transgenic soybean plants resistant to glyphosate. They are commercially available for the first time in 1996.
This technique is widely extended to other varieties of cotton, maize, or colza, making Monsanto the principal (and controversial) supplier of transgenic varieties.
Main Benefits: The use of these GMOs allow for the significant reduction of herbicides used, no time restrictions (use is independent of the growth cycle of the plant), increased control of weed populations, a reduction in the risk to the populations of small field mammals (since the glyphosate intervenes only on a plant enzyme chain), and a reduction in pollution and the persistence of the herbicide used.
Main Controversies: However, some points of this technique are strongly debated. It appears that certain types of weeds grow that are also resistant to glyphosate, as well as the appearance of the genetic material, known as genetic pollution, which can potentially contaminate surrounding organisms. In the case of grasslands, this concerns mainly transgenic pollen (notice immediately that this problem of pollen flow can be adjusted in grasslands with an early cut, before the appearance of pollen). These issues are added to the existing debate on social issues and ethics.
Two factors are used to measure a quality of fodder: its energy value (the energy contained in the fodder) and digestibility (the ability of the fodder to release its nutrients during digestion). In order to constantly maximize the performance of grasslands, it is important to have good quality forage. It is necessary to keep in mind that livestock need a certain amount of nutrients. The higher the forage quality, the smaller the quantity necessary to meet animal needs. As more and more farmers desire to be independent in terms of feeding their livestock, increasing the quality of their forage allows for a reduction of the required inventory, which is at the same time an infra-structural and economic benefit.
Some research programs work on improving the energy value of a forage, or its digestibility, which depends on three factors: the lignin content, the nature of binding agents (the hemicellulose molecules), and the differences in composition. The lignin content (present in the walls of the plant and especially involved in its maintenance) changes during the growth of the plant, increasing during maturation. However, lignin is not well digested by animals and thus reduces the digestibility of the forage element. Thus were obtained, by inhibition of the enzymes responsible for the synthesis of lignin, the hypolignified varieties with increased digestibility. These new varieties are Lucerne and high fescue.
A lignin is composed of structural units responsible for the formation of so-called “phenylpropanoid” H, G (Guaiacyl) and S (Syringyl) elements. It was noticed that with an increasing S/G ratio, digestibility was decreasing. Researches are also focusing on ways to (genetically) reduce this ratio.
Important genetic progress was made in the principal forage species and was the object of a recent syntheses by van der Heijden and Roulund in 2010¹ (tableau 1) et Sampoux et al en 2010² (Table 4).
Genetic progress is made on the aspects that are considered selection objectives. They concern:
Resistance to diseases
Tolerance to abiotic stress
and in less important way:
The aspects concerned
The ability to symbiosis
The value of animal products resulting from the fodder usage.
Table 1 summarises the variation of these objectives of selection against forage grasses and legumes.
A summary of genetic progress on biomass production was proposed by Wilkins and Humphreys in 20034) for different species where most of the studies showed, with the exception of those conducted by Laidig et al in 2008, progress on the production of the total biomass at a rate of 1 to 6% per decade.
In the same way, the important progress were observed on diseases.
Sampoux et al. sought in 2010 to quantify the genetic progress obtained on the perennial ryegrass for various characters, that they are characteristic of production, quality, or resistance to diseases.
The important progress was demonstrated in regards to:
Resistance to crown rust
Reduction of booting (that improves the usage value)
Important improvement of the total biomass production (at a rate of 0.29 tonnes/ha for every ten years) that is attributed in particular to the increase in summer production (this may also be related in part improved resistance to diseases).
Unexpectedly, considering that it was not part of the main objectives of selection, there is an increase in the soluble sugar contents and an improvement of digestibility.