Ensure your organic ingredients are compliant: CMS

 This article is also available in French: 

Cytoplasmic male sterility (CMS) is a tool used in agronomy to exploit hybrid vigour or heterosis in plants. However, the use of hybrid seeds is strongly discouraged by some members of the organic farming sector.

What is cytoplasmic male sterility? How is it obtained? Are CMS hybrids GMOs? Can they be detected to guarantee the characteristics of the ingredients of your products, especially when developing an organic range?

Male sterility concerns plants that are unable to reproduce by self-pollination due to sterility of the male elements of the flowers.

Male sterility is used by breeders to produce hybrid varieties in cultivated species such as wheat, cabbage and rape. Yield is increased using hybrid vigoro or heterosis. Male sterility, which also exists naturally, can be obtained in laboratory conditions: either genic known as GMS, or cytoplasmic known as CMS. Let’s take a closer look at the CMS method for which the company Food Chain ID has developed a detection method.

What is cytoplasmic male sterility? How is it obtained? Are CMS hybrids GMOs? Can they be detected to guarantee the characteristics of the ingredients of your products, especially when developing an organic range? ?

Why cytoplasmic male sterility (CMS)?

Why develop a plant sterilization method?

To produce a hybrid seed variety of a plant, both a male and female line are required. The plant must be sterilized, either manually or chemically, to obtain the main line. But these methods are not always easy or feasible in large-scale seed production. It was therefore necessary to develop other methods to obtain sterile male lines. (Source: GNIS)

Male sterility is the inability of plants to reproduce through self-pollination because the male elements of the flowers are sterile. This is naturally the case in many plant species such as onion, carrot, beet and fennel. Alone, these plants cannot reproduce themselves. They need to live within a population to reproduce, and if they do not belong to a strictly autogamous species such as tomato or rice, they can be fertilized by normal individuals (fertile males) which ensures their reproduction (source: Wikipedia).

How is a sterile male line obtained?

If it does not exist naturally, cytoplasmic male sterility can be obtained in two ways:

• By transfer to a cultivated species through natural hybridisation with a similar species which naturally features male sterility
• In laboratory conditions, with a cultivated species, using male sterility from a species of the same family that the cultivated species naturally crosses with. This is done using biotechnology with protoplast fusion.

Protoplast fusion (or somatic fusion) is a form of genetic modification that merges two plant species into a new hybrid. The hybrid inherits the genetic properties of the two original species. Georges Pelletier, researcher at INRA, was the first to master this method in his research into the genetic determinism of cytoplasmic male sterility. (Source: INRA).

Protoplast fusion can also be used to restore plant fertility, so CMS is reversible.

The brassicae family (cabbage, cauliflower, turnip, rape etc), endive and chicory are the most conducive to CMS.

Brassicas

Some plants have naturally sterile male lineage. In some cases, such as hybrid rye, male sterility can even be achieved with conventional hybridization techniques.

But in most cases, it is technically very difficult to obtain a sterile male line. This is when researchers use protoplast fusion. For example, fusion of Japanese black radish cells with cauliflower cells was used to intentionally obtain a sterile male cauliflower line. Studies conducted by Hiroshu Ogura into the Japanese radish in 1968 enabled this advance. Japanese radish was chosen because of its common characteristics with cauliflower, yet the possibility of them breeding together naturally is statistically unlikely.

What are the advantages of cytoplasmic male sterility?

Cytoplasmic male sterility allows the production of hybrid seeds. The aim of hybridization between two types of plants is to benefit from a heterosis effect. The heterosis effect (or hybrid vigour) is when first-generation hybrids (called F1) obtained by crossing two pure lines have a higher agronomic value than that of the two parents.

Producing F1 hybrid seeds is an important solution to major important economic issues in farming. They provide better yield. It is currently estimated that more than half of the production of field crop species such as maize, rice, sorghum, or sunflower comes from hybrid varieties (Source: Vegenov).

The debate about cytoplasmic male sterility

Are CMS seeds GMOs?

European regulation defines GMOs as “a living organism whose genetic heritage has been modified by human intervention”. These changes must be derived from genetic engineering, i.e., by suppressing or injecting DNA into the organism.

According to European Directive 2001/18/EC, CMS hybrids generated by proto/cytoplast mergers are not considered to be GMOs, as the resulting plant could also have been obtained in a classical manner.

Voluntary GMO-free labelling exists in France, however CMS-free labelling does not.

CMS hybrids and organic farming

Legally, CMS varieties are not GMOs and are therefore authorised for use in organic farming. However, the organic sector, from producers to processors, does not approve of their use as they are the result of genetic engineering.

Organisations promoting organic farming in Germany and around the world, such as Demeter, have strongly discouraged the use of CMS hybrid seeds and published lists of seeds to be banned. For example, the list includes many varieties of cabbage (source: Demeter).

In France, many organic companies including BioBreizh, Bio Loire Ocean and Biocoop have banned hybrid CMS varieties from possible crops. Traditional players in the retail sector such as Carrefour are campaigning for the sale of heritage seeds rather than hybrid seeds (source: Carrefour).

Being able to detect CMS hybrids

That is why Food Chain ID has developed a CMS hybrid detection system, as explained by Dr. Konstantin Rizos, R&D director of Food Chain ID Testing, "European regulations are very clear: CMS are not GMOs yet they are rejected by many organic associations. These tests are an essential tool for members of the food industry who want to ensure the traceability of ingredients in their organic products.”

Food Chain ID Testing offers a CMS detection method that concerns two main plant species: cabbage and chicory. For cabbage, Japanese radish cells are fused with cabbage cells (CMS Ogura). In the case of chicory, sunflower is used.

In both cases, genetic information is encoded in the mitochondrial DNA of cytoplasms. Food Chain ID testing has developed a special polymerase chain reaction (real-time PCR) method to measure the initial amount of Ogura radish or sunflower DNA in hybrids. Real-time PCR consists of duplicating a large number of DNA sequences from a small amount of nucleic acid which detects the presence of foreign DNA. This detection method can be used on both cabbage and chicory samples.

Food Chain ID Testing is continuing to develop new testing methods to ensure the traceability of ingredients to assist the food industry.

Keywords

Sustainable Agriculture, Organic Agriculture, AgTech, Agronomy

Further reading

• Belliard G, Vedele F, Pelletier G. 1979. Mitochondrial recombination in cytoplasmic hybrids of Nicotiana by protoplast fusion.Nature 281, 401-403
• Pelletier G, Primard C, Vedele F, Chetrit P, Remy R, Rousselle P, Renard M.1983. Intergeneric cytoplasmic hybridization in Cruciferae by protoplast fusion. Mol Gen Genet.191, 244-250
• Bonhomme S., Budar F., Lancelin D., Small I., Defrance M-C., Pelletier G. 1992. Sequence and transcript analysis of the Nco2.5 Ogura-specific fragment correlated with cytoplasmic male sterility in Brassica cybrids. Mol Gen Genet.Nov 235 , 340-348
• OGURA, HIROSHI (1968) Studies on the New Male-Sterility in Japanese Radish, with Special Reference to the Utilization of this Sterility towards the Practical Raising of Hybrid Seeds; Me. Fac. Kogoshima Univ. 6: 39 - 78