Growth and Bioactive Properties of Native Potatoes under Drought Stress - Development of an Integrated Approach from the Field to the Market

Abstract

The aim of this doctorate was to explore the potential contribution to food security of ancient genetic resources of crops, from the field to the market. Special attention was given to the resistance to drought stress, in the context of climate change, and to the production of bioactives potentially useful for human health. This project encompassed a broad diversity of topics, from fundamental sciences to social sciences, and was constructed around the case model of the potato crop, fourth staple crop worldwide in terms of tonnage produced. Focussing on Chile was another deliberate selection that was done in the beginning of the thesis: The genetic resources of potato from this country were assessed regarding their tolerance to drought and their production of health promoting bioactives. This genepool was chosen because of its diversity of landraces, and because it has not been given strong attention so far in scientific literature. Additionally, the cultivation of native Chilean potatoes is tightly linked to traditional small-scale farming systems, which may be threatened by globalisation and large-scale farming systems. These reasons call for more extensive description of the potential of potato landraces from Chile to contribute to food security. In chapter 2, the value of Chilean native potatoes was determined as a source of bioactives, especially of polyphenols and anthocyanins. These compounds are partly responsible for the interesting antioxidant properties of these potatoes, hinting on their potential interest as functional food rich in antioxidants. From this experiment, we could observe a diverse composition of bioactives across 14 genotypes, varying up to 10 fold regarding anthocyanin content. Moreover, a critical difference between samples analysed raw or cooked was observed, calling for caution in the interpretation of results from the numerous studies carried out only on raw samples. Additionally, the link between total polyphenols (TPC) and antioxidant activity (ORAC) could be clearly observed across all the samples. Investigating the profile in phenolic acids of these 14 Chilean landraces, we observed that caffeic acid was the major phenolic acid in these potatoes, followed by chlorogenic acid, which accounted for 61-85% and for 10-25%, respectively, of the content of phenolic acids detected in cooked samples. The interesting amounts of bioactives detected in this study, combined with the extent of their variation between genotypes, suggested the possibility of breeding potatoes for increased contents in anthocyanins and other phenolic compounds. In chapter 3, I detailed the response to drought stress of nine potato genotypes, including the commercial variety Désirée. The trial was conducted in field conditions in the south of Chile, with a plastic mulch preventing the rain from interfering with the drought treatments. Water was provided through drip irrigation, installed below the plastic foil. Two treatments of drought stress were implemented in distinct plots 88 days after planting (DAP) and 110 DAP, respectively, for a duration of six weeks. This experiment showed a strong negative impact of the drought treatments on the yield, on average 42% for the treatment 88 DAP and 23% for the treatment 110 DAP. The number of tubers produced for plant was also reduced by 40% and 12% for the treatments 88 DAP and 110 DAP, respectively. The impact of drought was genotype specific. Considering bioactives in the tubers, drought did not have any effect on their concentration. However, because of the reduction of the yield, the production of bioactives per ha was reduced, which could impact negatively the production of nutraceuticals based on potato tubers. Furthermore, the concentration of starch and bioactives (resistant starch, total phenolics, anthocyanins) as well as the antioxidant activity were genotype dependent, validating the potential of native Chilean potatoes for plant breeding programs targeting nutrients and bioactives. The 4th chapter of this thesis presented how ancient genetic resources can be useful for food security and the economy, and gave rationales for their conservation, in an attempt to bridge agricultural sciences and policy sciences. Currents trends on the conservation and the use of potatoes and potato genetic resources 7 in Chile were analysed, as well as the bio-physical, socio-economical and political factors conditioning the conservation and use of potato genetic resources in Chile. Via an exploratory study combining qualitative interviews of the stakeholders of the Chilean food chain with a semi quantitative survey of Chilean consumers, it was possible to test the interest of the Chilean food chain for potato products with specific qualitative aspects, including functional food. The two main outcomes of this study were a) strong interest for attractive colours and high contents of antioxidants and b) willingness to pay a higher price for potato products presenting demonstrated health benefits. Interestingly, a high proportion of the interviewed consumers had knowledge about antioxidants, and could associate them with a positive contribution to health and welfare. Overall, this approach allowed us to verify that the Chilean food chain perceived Chilean potato landraces as a valuable resource, and showed interest for new products that are highly colourful. Additionally, the concept of functional potato food, in this case potatoes enriched in antioxidants, was positively received by the consumers. The results of the individual chapters show the complexity but also the high potential to improve the food chain of a certain region with a specific, so far underexploited product. These considerations are discussed in the context of global food security, for which not only an increased access to healthy food but also the consideration of the limitation of the food demand seems to be a highly relevant and underexplored aspect.