Use of Genetic Markers in Wheat Breeding for Organic Heterogeneous Material

Anders Borgen, Dennis Kjær Christensen

Agrologica, Mariager, Denmark

Keywords: OHM, MAS, common bunt, marketing.

 Abstract: Organic Heterogeneous Material (OHM) is a term defined in the EU Organic regulation (EU 2022), and based on experience gained from several EU projects on organic plant breeding. OHM can be composed by mixing of all offspring from a set of crosses exposed to natural selection (original composite cross populations), but the mixture will in this way be similar or slightly better than the average of the parents (Döring et al., 2011). It is therefore crucial to use only well adapted parents to achieve competitive germplasm. If suboptimal parents are included, an alternative approach such as positive and negative selection by the breeder need to be used to avoid suboptimal components, and the EU regulation allows this. One way to avoid sub optimal genotypes in OHM is to select pre studied pure lines, and compose the OHM only by selected offspring (complex variety mixture).
Organic plant breeding at Agrologica started in Denmark 2006 with the attempt to develop OHM of wheat with good baking quality, weed competition and resistance to plant diseases, including common bunt.
Some traits are difficult but not impossible to improve further after the OHM have been composed. Baking quality can be improved by Single seed NIR sorting (eg. BoMill Insight^® technology), colour sorting or by gravity sorting. However, with state-of-the-art technology, this can only increase gross grain protein content and seed hardiness, but will not improve more complex baking quality parameters such as gluten rheology, incl. gluten index. To compose mixtures with optimal gluten index above the average of the parents, we have developed SNP markers for High Molecular Weight Glutenin subunits (HMWG) to be used for MAS in order to compose mixtures with a diversity of optimal HMWG subunits within the mixture.
Weed competition is best improved by visual assessment and selection for early vigour, and plant height before heading stage with due respect of the risk of lodging. The plant height, lodging resistance and early vigour are governed by a high number of genes, including genes for vernalisation, and genetic markers are developed for some of these genes, but so far, our selection mainly rely on phenotyping, with only limited support from MAS.
Cereal Cyst Nematodes (CCN, Heterodera avenae) is in Denmark mainly a problem in spring wheat, and no varieties on the EU Catalogue are documented to be resistant. The market for special varieties with this trait is limited as farmers tend to use non susceptible crops rather than resistant cereal varieties in case of nematode infestation of a field. Therefore, CCN resistance should be included in all spring wheat as a preventive rather than a curative measure. Marker Assisted Selection (MAS) is the best way for selection, as field phenotyping is difficult and expensive. We have therefore developed SNP markers the Cre1 resistance gene for this selection.
Common bunt (Tiletia caries) needs special attention in organic breeding programs, as most varieties are susceptible (Borgen et al., 2023A). Only a few susceptible plants in an OHM are enough to maintain an infection, and close to all plants must therefore have resistance to the virulence in the region. Virulence is present in Europe against most of the known resistance genes (Borgen et al., 2023B), and pyramiding genes are therefore the only safe way for durable resistance to common bunt. We have so far identified 59 resistance genes and developed SNP markers to 20 of them for MAS (Christensen and Borgen, 2025).
Leaf diseases such as mildew and in particular rust diseases (Puccinia sp.) can be devastating in organic farming. These diseases can be selected in the field based on leaf symptoms, but the experience indicates that if resistance is based on a single or few vertical resistance genes, the varieties or OHM can turn susceptible within 1-3 years. Therefore, horizontal (adult plant) resistance genes or multiple vertical resistance genes must be included to maintain durability of the resistance. We therefore develop SNP markers for the most important rust resistance genes for MAS.
We conclude that OHM is preferable over pure line varieties as a strategy for organic farming, as both yield and baking quality is more stable than in pure line varieties. Our experience is that OHM based on selection of pure lines in many cases provide an appropriate strategy to develop high quality germplasm for organic farming. There seems to be a synergy of baking quality and taste between the components of a mixture.
Funding organic plant breeding is difficult as the market is too small to cover the cost of the breeding. The OHM developed from our breeding program is therefore distributed via the member organisation Landsorten, based on home saved seed production to reduce cost for the seed production. Two OHMs have been officially registered, ‘Mariagertoba‘and ‘Popkorn’, whereas other OHMs are produced in smaller amount without registration. By not selling seed, the activities of Landsorten are legal, and small seed lots can be distributed under the Article 3 exemption or research, trial and breeding purposes (EU 1966) as a base for multiplication of home saved seed. Landsorten supports in this way a production of 1500 ha of organic bred varieties in Denmark, England, Belgium and The Netherlands.

Acknowledgements: The breeding, seed production and research is supported by the CORE Organic Co-fund project ‘DIVERCILIENCE’ and the Organic RDD project ‘BOOST’ funded by GUDP, Denmark, both coordinated by ICROFS.

References:
Christensen D., and Borgen, A., 2025. Mapping Bt-resistance genes controlling common bunt in wheat. Abstracts of The XXIII International Workshop on Bunt and Smut Diseases.
Borgen, A., Müller, K.-J., Vollenweider, C., Löschenberger, F., Henriksson, T., Christensen D.K., Dumalasova, V., 2023A. Registered varieties and Organic Heterogeneous Material (OHM) with resistance to common bunt in Europe. Bürstmayr, Hermann (Ed.) Proceedings of the XXII International Workshop on Bunt and Smut Diseases, BOKU, Austria, 28-29.
Borgen, A., Forster, M., Sedaghatjoo, S., Christensen, D.K., Maier, W., 2023B. Determination of virulence of European races of common bunt using a differential set of wheat cultivars. Bürstmayr, Hermann (Ed.) Proceedings of the XXII International Workshop on Bunt and Smut Diseases, BOKU, Austria, 16-18.
Döring, T.F., Knapp, S., Kovacs, G., Murphy, K., Wolfe, M.S., 2011. Evolutionary Plant Breeding in Cereals - Into a New Era. Sustainability, 3(10), 1944-1971, https://doi.org/10.3390/su3101944
EU, 1966: Council Directive 66/402/EEC on the marketing of cereal seed.
EU, 2022: Regulation 848/2018, on organic production and labelling of organic products.