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Lab equipment. © INRA, William Beaucardet

Green biotechnologies: paving new paths for agriculture

Association genetics and marker-assisted selection

The purpose of markers is to assemble the maximum amount of desirable traits in a plant of a given species destined for food or agribusiness. To that end, the gene or genes that govern each trait must be identified so that they may be transferred to varieties of agronomic interest. 

Association genetics, to access complex traits

Certain traits with high agronomic potential, such as resistance to drought or temperatures, or good nitrogen recovery from soil, are complex and governed by several genes of partial effect known as QTL (Quantitative Trait Loci).

Automatic phenotyping platforms capable of analysing thousands of specimens in a short time have been developed at INRA in Montpellier. © OURY Vincent
Automatic phenotyping platforms capable of analysing thousands of specimens in a short time have been developed at INRA in Montpellier. © OURY Vincent
Association genetics is a recent method of accessing complex traits without having to sequence all of the genes involved. It also allows for a large number of genotypes to be tested and therefore a wide spectrum of genetic diversity to be studied. Association genetics consists of statistically associating variations in traits (phenotypes) and variations in genomes. To do this, several conditions must be met: a large sampling of specimens must be assembled to best represent natural diversity, and access must be gained to phenotyping and high-throughput genotyping. Automatic phenotyping platforms capable of analysing thousands of specimens in a short time have been developed at INRA in Montpellier. Where genotyping is concerned, innovation lies in the creation of chips: simple small glass plates that contain thousands of polymorphism markers, allowing scientists to detect genome variations. These chips are being developed for more and more plant species.

To identify genotypes of interest

Film shot at INRA Montpellier where scientists have a unique experimental platform at their disposal.

It enables a simultaneous quantitative analysis of the behaviour of 1,650 plants, cultivated in a greenhouse, that can highlight the most interesting traits to enable the selection and improvement of species of agronomic interest. This operation has been made possible thanks to exceptional funding from INRA and the support of the Languedoc-Roussillon Regional Council and other partners (CNRS, CIRAD, Université Montpellier 2 and Montpellier SupAgro).

To make better use of natural diversity

In a few years’ time, scientists hope to be able to identify the best allele combinations (different versions of a gene with differing sequences) to improve resistance to drought. Markers can then be used to create new varieties with these new combinations.

“Association genetics allows for a more integral approach to genomes, because it sheds light on all the genomic regions that determine traits, without prior knowledge of a given function”, says Alain Charcosset.

According to Etienne Hainzelin, consultant to the CEO of CIRAD, “Thanks to association genetics, we are able to explore genetic diversity and find genotypes that are adapted to the constraints of a given place (drought, disease, etc.). It is the opposite approach of standardising a place (by irrigation, fertiliser, pesticides) and using different high-tech varieties that are fragile and compromise the genetic base of a crop when used on a large scale.”

Marker-assisted selection: accelerating crossbreeding

Markers serve to identify genes that confer beneficial agronomic traits on a plant, even if the genes themselves have not been identified. Over the course of successive crossbreeding, it is simply a question of looking for markers to sort those specimens which have retained the beneficial genes, without having to test them out in the field. This technology is now widespread in the selection process.

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Associated Division(s):
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Point of view

Plant selection, one of the cornerstones of human civilisation

There is no crop that has escaped modification by man since its domestication. While the transformation of wild plants into cultivated crops has occurred slowly over thousands of years by the selection of spontaneous mutations, planned improvements of plant varieties began about two centuries ago, after the discovery of the laws of inheritance by the Czech monk Gregor Mendel of Brno. The selection of plants is one of the cornerstones of human civilisation. For example, the domestication of maize, the second largest crop in the world, is a long process of the transformation of teosinte, cultivated in Mexico some 7,500 years ago. Teosinte is so different from the maize we know today that only recent studies in molecular biology have revealed it as the ancestor of maize.