Potato is the most important non-cereal crop worldwide. It has been consumed in the South American Andes for thousands of years and then introduced to Europe in the XVII century. Thanks to its nutritional value and high yield it was then expanded to the rest of the world. Since potato is a staple food crop for many countries, it plays a crucial role in maintaining food security and reducing malnutrition. Unfortunately, the sustainable production of this crop is threatened by climate change that causes rising global temperatures and altering weather conditions all over the world.

The main purpose of this study was to understand how weather variables affected by latitude and year impact the biosynthesis of phenolic compounds and ascorbic acid in pigmented potato cultivars. The first aim of this work was to develop reliable extraction methods for anthocyanins and ascorbic acid, as previous studies showed contradictory information on the anthocyanin content when using fresh, freeze-dried or steamed potatoes. The second aim was to assess the effect of temperature, cultivar, and tuber developmental stage on the expression of genes involved in the biosynthesis of phenolic compounds and the content of anthocyanins, phenolic acids, and ascorbic acid in potato cultivars with purple or yellow flesh and/or skin. The third aim was to evaluate the effect of weather conditions (affected by latitude and year), cultivar, and tuber developmental stage also on the gene expression levels and on the content of anthocyanins, phenolic acids, and ascorbic acid in potato cultivars grown at two different latitudes and two consecutive years in Finland.

The results showed that anthocyanins were most effectively extracted from freeze-dried potatoes using 70 % acidified methanol. Tris(2-carboxyethyl) phosphine hydrochloride was the most effective in reducing dehydroascorbic acid to ascorbic acid and was therefore the most suitable reducing agent for the determination of total ascorbic acid.

Cultivar was the main variable that affected the gene expression levels of the enzymes involved in the biosynthesis of phenolic compounds as well as the anthocyanin and phenolic acid profile. The main anthocyanin in the purplefleshed and purple-skin cultivars was a petunidin derivative or malvidin derivate (depending on the cultivars), while the main anthocyanin in the red-skinned cultivar was a pelargonidin derivative.

The effect of tuber developmental stage was evaluated in the second and third aim of this study. In both cases, it was found that the content of the main anthocyanins and phenolic acids as well as ascorbic acid tended to decrease with tuber maturation, although the content of minor anthocyanins and phenolic acids did not show a clear tendency to increase or decrease. The gene expression levels also remained relatively stable for most of the genes studied except for F3ʹH which showed a clear decreasing trend during tuber development in the purplefleshed cultivars.

When potato tubers were cultivated under controlled temperatures (at 13 and 18 °C), it was found that the studied temperatures did not affect the content of anthocyanins, but mildly affected the content of phenolic acids and ascorbic acid during tuber development. However, when tubers reached full maturity no significant differences in the content of anthocyanins, phenolic acids or ascorbic acid were observed between the tubers grown at the two studied temperatures. Our third aim was to evaluate the impact of latitude on the content of phenolic compounds and ascorbic acid in potato tubers, and for that we evaluated two latitudes and replicated the experiment in two consecutive years for repeatability purposes. However, when we processed our data, we realized that the synthesis of the metabolites of interest were mainly affected by the interaction of “Latitude: Year” and less by the solo effect of “Latitude” or “Year”. So, when potato tubers were cultivated at different latitudes (61.2 and 64.8° N) and years (2014 and 2015) in Finland, potato plants cultivated at 61.2° N in 2014 (Kokemäki) were exposed to temperatures above 18 °C and reduced precipitation events. The pigmented potato tubers produced in this trial had the lowest expression levels of most of the genes involved in the phenylpropanoid pathway and the lowest content of phenolic compounds and ascorbic acid. On the other hand, when potato plants were cultivated at the same latitude (61.2° N) but in 2015 (Köyliö), the plants were exposed to temperatures between 13 and 18 °C and good precipitation events. These plants produced tubers with the highest gene expression levels, as well as the highest contents of anthocyanins and phenolic acids. The potato plants cultivated at 64.8° N in 2014 and 2015 (Muhos) produced tubers with intermediate contents of anthocyanins, phenolic acids, and ascorbic acid. Positive gene-gene, gene-anthocyanins and anthocyaninanthocyanin correlations were also stronger and more significant at 61.2° N in 2015 (Köyliö) than in the other field trials.

In this study, we observed that a mild increment in temperature combined with poor precipitation events at 61.2° N in 2015 (Kokemäki) had a detrimental effect on the synthesis of bioactive compounds in potato tubers. However, during the last five years, temperatures in Finland have exceeded those of 2015 and Finnish potato growers have reported difficulties due to unexpected weather events. Further research is needed to better understand the potentially synergistic interactions of the main weather variables affecting the synthesis of bioactive compounds in potato tubers.