CIRAD – a grain of hope for rice growers?
A large number of crops currently rely on using first-generation hybrid varieties, obtained by crossing two genetically different varieties. These so-called “F1” hybrids are highly vigorous and sought after by farmers. However, that vigour is not sustained in the next generation. This obstacle obliges farmers to use new seeds every year, making them dependent on seed firms. What if it were possible to overcome this, to sustain the properties of hybrid plants from generation to generation?
For the time being, matters are still in the experimental stage, but the results are there. A team from the French research institute CIRAD in Montpellier, in association with researchers from UC Davis in California/USA, the Max Planck Institute for Plant Breeding in Cologne/Germany, the Institut de Recherche pour le Développement (IRD) in France and the Council for Scientific and Industrial Research (CSIR) in Ghana, recently demonstrated that it was possible to reproduce a hybrid rice variety identically from seed. This means that the variety could be cloned infinitely while retaining its original properties.
This cloning mechanism already exists naturally in a large number of plant families. It is called "apomixis", referring to asexual reproduction without fertilisation, in which seeds are produced that are genetically identical to the mother plant. In rice, however, the phenomenon does not exist in the wild. The research team managed to create synthetic apomixis, using genome editing techniques.
Emmanuel Guiderdoni, a rice genome specialist from CIRAD who supervised the study published in Nature Communications, sets out the results: "Ninety-five per cent of the grains obtained are clones; in other words they have the same properties as the initial F1 hybrid, including grain quality. The progenies retain the same genome over several generations. In practice, this means that farmers will no longer need to buy new seeds every year; they will simply be able to sow some of the grains they harvest.”
Such an advance would be of particular benefit to the poorest rice growers, who could keep seeds of hybrid plants without losing their high yield potential. Matilda Ntowa Bissah, a geneticist at CSIR Ghana and co-author of the study, says: "If the technique were applied on a large scale, it would improve access to good seeds for resource-poor farmers and boost productivity and incomes.”
However, the researchers stress that the work is far from finished. "For instance, for the moment, the hybrids obtained are less fertile. In other words, they produce fewer grains than the original hybrid,” they explain. “We therefore need to correct this defect before we can think about field trials. This will take years.”
Synthetic apomixis using genome editing techniques
Wild and cultivated rice species naturally reproduce sexually, which results in genetic mixing and progenies that differ from their parents. To conserve the vigour of an F1 hybrid, the researchers therefore sought to trigger embryo formation artificially, without either genetic mixing or fertilisation, what is known as apomixis, a type of cloning.
To do so, they called upon genome editing techniques, using the CRISPR-Cas9 system. "We inactivated three genes and added a modified gene from the rice itself,” Emmanuel Guiderdoni explains.
Objectives: access to seeds and diversification
F1 hybrids are known to remain more productive and more stable in the event of environmental fluctuations. However, at present, such hybrids are highly complex and costly to produce in the case of rice, which makes them inaccessible to small-scale rice farmers.
Synthetic apomixis would allow two things. First, it paves the way for diversifying F1 hybrids much more easily, for instance to create varieties tailored to local demand and to different climate situations. Secondly, provided national research systems take the technique on board, synthetic apoximis could give farmers a degree of independence from seed firms, since they could reproduce these improved varieties themselves.
Aurore Vernet, Donaldo Meynard, Qichao Lian, Delphine Mieulet, Olivier Gibert, Matilda Bissah, Ronan Rivallan, Daphné Autran, Olivier Leblanc, Anne Cécile Meunier, Julien Frouin, James Taillebois, Kyle Shankle, Imtiyaz Khanday, Raphael Mercier, Venkatesan Sundaresan, Emmanuel Guiderdoni. 2022. High-frequency synthetic apomixis in hybrid rice. Nature Communications