Development of molecular markers as tools for breeding potatoes rich in anthocyanin

Secondary plant metabolites in human nutrition

Even in industrialized countries with an excellent food supply and variety, fruit and vegetable consumption is often relatively low and well below internationally recommended amounts. We cover most of our diet with a few basic foods such as rice, corn, wheat and potatoes. A predominantly plant-based human diet, especially if based on fruits and vegetables, can make a valuable contribution to human health. Since in addition to the classic macronutrients carbohydrates, proteins and fats, plant foods always contain secondary plant metabolites.

Secondary plant metabolites are organic compounds that are generally found in specialized cells where they play an important role for the entire plant, e.g. in protecting it from predators or through their attractive coloration. Many of the secondary plant metabolites also have positive effects on human health, which scientists are taking advantage of. For example, many pharmaceuticals are based on plant secondary metabolites. But even today, the mechanisms of action of some secondary plant metabolites are still obscure. One large group of secondary plant metabolites are the water-soluble anthocyanins, which belong to the group of flavonoids. They are found in cell sap of almost all higher plants. They also occur in the flowers and fruits, where they are responsible for the partly intensive red, violet or blue coloring. Hence, their name. It consists of two parts: Ánthos, the ancient Greek word for flower, and kyáneos, the ancient Greek word for dark blue or dark color.
Anthocyanins have three main functions in plants: They absorb the short wavelength UV light of the sun and and re-emit the radiant energy as heat. This is how proteins and DNA molecules in the cells are protected from the harmful effect of the UV rays. In addition, the intense coloring attracts insects and other animals. Thereby ensuring the propagation and distribution of the plants. The anthocyanins also have a strong antioxidant effect. If the plant is exposed to oxidative stress, free radicals are formed, among other things, which react with oxygen molecules to form reactive oxygen radicals and have a negative effect on the plant's metabolism. Free radicals are also suspected of being associated with various diseases in humans. Anthocyanins are able to render free radicals harmless and are therefore said to have health-promoting effects. Studies in humans and animals have shown that anthocyanins have anti-inflammatory, anti-viral and anti-carcinogenic properties. In addition, positive effects on cardiovascular disease, obesity, increased cholesterol levels and memory performance were observed.

Most staple foods, such as wheat or rice, are relatively poor in anthocyanins, so fruit and vegetables are currently the main source of anthocyanins in human nutrition. Potatoes are an exception, as old, lesser known blue- and red-fleshed potato varieties whose color is due to the presence of anthocyanins exist, in addition to the yellow- and white-fleshed ones.

Especially in South America many colored old landraces are still to be found, which can be used for the breeding of modern efficient potato varieties with a high content of anthocyanins.

Potato breeding with molecular tools

Potato breeding is a complex process and in particular the genetics of quantitative traits such as the anthocyanin content in tuber flesh is difficult to resolve. New varieties are developed using combination breeding by crossing two varieties or clones with desired properties. The crossing and selection processes to breed a new potato variety in the classical way take about ten to fifteen years.

However, by using molecular markers for different traits, this process can be shortened considerably. Early in the selection process, we can identify the offspring that will express the desired traits. For example, plants that are resistant to certain diseases could be selected without having to conduct very expensive resistance tests in the field or greenhouse. Such an approach is called marker-assisted selection or "smart breeding." For certain traits, the use of such markers is indispensable. For example, if colored landraces are crossed with uncolored elite varieties, uncolored offspring may result because important alleles for anthocyanin production are segregated. To restore the high anthocyanin trait, lines containing different complementary alleles must later be combined in further crosses. Therefore, such beneficial alleles need to be identified at the molecular level to provide the necessary tool for such breeding, the objective of the binational cooperation project "MoMaPo".

The partners involved, Universidad Austral de Chile, Fraunhofer Chile Research, and Fraunhofer IME had access to the potato gene bank of the Universidad Austral de Chile, which represents the exceptionally high biodiversity of Chilean potatoes. An important group of this genebank are the potatoes collected in the area of Chiloe Island, which are characterized by a particularly high diversity in the trait colored tubers. 290 of these plants were analyzed for potential markers of increased anthocyanin content. Bioinformatics was then applied to associate the results obtained with the anthocyanin content, enabling the identification of molecular markers. In the future, these can be used to breed high-performance varieties with colored tuber flesh.