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The Rheintaler Ribelmais within the Swiss maize landraces

Importance of landraces

Landraces were the common form for many crops before new breeding techniques were used to develop todays crop varieties, which are grown commercially all over the world. For centuries, crop landraces were the principal focus for agricultural production, where farmers have sowed, harvested and saved seed to use again for the upcoming year. This workflow has enriched the genetic pool through intra-specific diversity. There is a vast heterogeneity within the landraces, which is contrary to the modern hybrid corn varieties, where every plant has the same genetic material. Due to the adaption of modern, high-yielding varieties, which have allowed the world population to grow and evolve during the Green Revolution, landraces have been abandoned and lost in some cases. This has also led to a loss in genetic diversity and genetic material for further breeding. This type of loss is also called as genetic erosion and is also embedded within the UN sustainability goals. In the face of Climate change, the adaption of important staple crops, such as corn, Rice and Wheat to a changing climate is as important as ever to feed a growing world population. Finding and conserving landraces all over the world is therefore important for enhancing the genetic pool to breed adapted and robust varieties.

Swiss Landraces

Switzerland has a broad genetic diversity of maize landraces, which are also distinguishable to the genetic pools of neighbouring countries. Technically, the landraces such as the Rheintaler landrace are not separated and independent varieties but a collection or pool of maize plant populations grown in the same region. Genetic analysis from the defined swiss core collection for maize from Swiss regions with ancient maize production, such as the Ticino, the rhine valley, Valais, posterior rhine and the Posciavo valley have shown the geographical diversity of swiss maize landraces. Furthermore, some region-specific allele were found, also indicating some genetic differences between the regions and thus partly a genetic separation within the Swiss landraces. This means that Swiss maize landraces cannot only be distinguished by the region, where they are grown but also, at least partly, genetically. However, there is also evidence that a strong genetic exchange through trade between the regions has happened. In the case of the “Rheintaler” landrace this exchange is likely to have happened with the adjacent region of the Linth valley but also along the southern parts of the alpine Rhine Valley. Between the northern and the southern landraces as well as the landraces from the Valais, a clearer separation of the genetic pools has been observed. More recent phylogenetic analysis has even identified two northern clusters . Upon these findings, three main groups of Swiss landraces can be distinguished; the northern landraces containing the Rheintaler landrace amongst others, southern landraces and landraces from Valais, which build an intermediate cluster. The genetic differentiation of the swiss landraces are thus in good accordance with the geographic separation caused by the Swiss Alps.

If the swiss landraces are put into an international context, the southern Swiss landraces from the Ticino are most similar to the Italian-Orange-Flint pool, whereas northern landraces are closely related to the Northern American flints, which is remarkable considering that corn was first brought to Europe from the American continent in the late 15^th century after the exploration of America by the Europeans.

The “Rheintaler” landrace

The products of the Rheintaler Ribelmais exclusively use maize produced from the Rheintaler landrace. It belongs to the Flint corn variant, which has hard corns with lower water content and is thus suitable for grinding and milling but not for cob- or popcorn production. Many landraces in Switzerland were named after the colour of their cobs (e.g. weisser Rheintaler). In the rhine valley, the cobs often have a light-yellowish colour, but also other colour-variants are known, whereas also a small (Kleiner Rheintaler) and big (grosser Rheitnaler) landrace type was defined. The two types differ in the count of the rows (8, 12 or 16) and the size of the corn.

The colour of the cobs varies across the swiss landraces and can even change over time due to the high diversity within the landraces and the random fertilisation of the open-flowering plants within the field. The sprinkled corns on the cobs, which can also occur on the cobs of the Rheintaler landrace long were a mystery until American scientist and Nobel Prize winner Barbara McClintock discovered the mechanism of the “jumping genes” Transposons in maize, which were responsible for the sprinkled corns.

Because of its white cobs, it is assumed that the white-corn varieties, which can be found southern of Venice may have been introduced to the rhine valley and influenced the colour of the cobs by crossing with the original landraces in the rhine valley. Through phylogenetic analysis it is today known that the Rheintaler Landrace originates from North American flint varieties, which were more suitable to the colder climate in northern and central Europe than the varieties from South America.