A grain of hope for rice growers: hybrid seeds that retain their quality from generation to generation

Results & impact 8 February 2023
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?
Planting upland rice, Vietnam © J-C. Maillard, CIRAD

Planting upland rice, Vietnam © J-C. Maillard, CIRAD

For the time being, matters are still at the experimental stage, but the results are there: a team from CIRAD, in association with researchers from UC Davis in California, the Max Planck Institute for Plant Breeding in Cologne, 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. In other words, the variety can be cloned infinitely while retaining its original properties.

This cloning mechanism already exists naturally in a large number of plant families: this is "apomixis", in other words asexual reproduction without fertilization, which produces seeds 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: "95% 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. For Matilda Ntowa Bissah, a geneticist at CSIR Ghana and co-author of the study, "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, while helping to achieve sustainable development goals* 2 and 8".

However, the researchers repeat 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. We therefore need to correct this defect before we can think about field trials, which will confirm the stability of these plants under field conditions. 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 fertilization, in other words 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: on the one hand, 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.

What is an F1 hybrid?

Hybrids are varieties created by crossing two distinct varieties. If the two varieties are genetically very different, the first-generation (F1) hybrid variety produced by crossing the two parents generally benefits from hybrid vigour. This means that its vigour, yields and taste quality are better than the sum of the characters of the two parents. Such F1 hybrids are thus highly sought after by farmers, and rice the most widely consumed cereal in the world, is no exception.

* The sustainable development goals, or SDGS, were established by the United Nations in 2015. There are 17 goals, to be achieved by 2030. SDG2 focuses on creating a world free of hunger, and SDG8 on decent work and economic growth.

Reference

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

See also