The exploitation of biodiversity may be useful in supporting food security and human nutrition and it contributes to a general sustainable development. Traditional food crops represent a precious source of biodiversity, and play a key role in supporting the identity of specific production areas, the consumer behaviour and the transfer of cultural heritage to future generations. However, these crops and foodstuffs require a preservation against the genetic erosion that may determine dramatic effects upon biodiversity, environmental sustainability and rural economies. This goal may be achieved through a detailed characterisation of these products, that allows emphasizing some traits useful to define their ‘ typicality’. In the past, the morpho-biometric approach was extensively used to characterise and differentiate genotypes and/or landraces within species. However, this methodology, based exclusively upon a phenotypic assessment, does not allow to easily discriminate between genotype and environment effects. The recent methodologies based on genetic markers allow to easily and rapidly discriminate species, cultivars and landraces. The high costs and the technical hitches to relate a phenotypic character to a gene expression make often difficult the application of these methodologies. Recently, beside genetic markers, the analysis of secondary metabolites has been proposed as an useful tool to discriminate within a given species. In this view, the metabolic profile may also allow to identify a large amount of local landraces that could counteract the globalization of crop production. Moreover, all these efforts for landraces characterization, in the context of European agriculture can be addressed to obtain protection of geographical indications (PGI) or protection of designation of origin (PDO) that strongly support the economic sustainability for farmers adopting typical landraces. This paper gives an overview of the main secondary metabolites occurring in plants and used as biochemical markers. Phenols are the most useful class of compounds for such chemosystematic studies, but other classes of compounds (notably carotenoids, alkaloids, volatile compounds, terpenes and sulphur compounds) have been also considered as potentially useful biomarkers for taxonomic purposes. In this paper, the application of the above-mentioned methodology has been described for tomato, onion, wheat, saffron, as case-study species. In long-storage tomato 16 different phenolic compounds have been identified, all belonging to the group of cinnamoyl-quinic acids and flavonoids. Tomato landraces with great differences in morphological traits but originating from the same area, exhibited a similar phenolic profile, thus revealing a common genetics. Moreover, the great genetic variability detected for the group of cinnamoyl-quinic acids derivates, indicates how these compounds may be used as reliable biomarkers to discriminate genotypes within this species. In onion, several researches revealed the validity of using flavonols as chemotaxonomic markers. Phenols and lignans have been proposed in several studied as markers to discriminate between old and new cultivars of wheat. Finally, the apocarotenoid profile allowed to well differentiate clones of saffron coming from several areas of the world.
Keywords: biomolecular markers, secondary metabolites, traceability, traditional crops