Tuscan Archipelago aromatic plants: chemical characterization and agronomic performance for the conservation strategies and adaptation to climate change

In the Mediterranean area, an increase in extreme phenomena such as droughts and floods are expected under the scenario of climate change (CC). The adoption of adaptation strategies is a crucial approach for mitigating the effects of these phenomena, especially in the agricultural sector. Diversification of agricultural production is ranked highest among the adaptation strategies; in particular the introduction of low-energy-input crops resistant to drought conditions has been shown to have a very important impact on food production. New crop opportunities and challenges for agricultural producers in Mediterranean farming systems are represented by Medicinal and Aromatic Plants (MAPs); indeed, they are generally adapted to withstand extreme drought conditions. Moreover, they have been shown to grow at low input levels and they are of interest to pharmacological, cosmetic and food technology industries. The research presented in this thesis provides information on the genetic, morphological and phytochemical variability of Helichrysum italicum subsp. italicum (Roth) G. Don grows in the Tuscan Archipelago islands and ultimately aims at encouraging the cultivation of this species in the area. The choice of this taxon has been motivated by characteristics such as its large diffusion on the Tuscan Archipelago islands, its medicinal and cosmetic uses, the high resistance to drought and the high economic value of its essential oil. The genetic, morphological and phytochemical analyses were conducted on the plants of 12 wild populations of Helichrysum growing in three islands (Capraia, Giglio, Isola d’Elba). A common garden experiment was also carried out to investigate the morphological and phytochemical variation occurring in the cultivated environment. The first experiment was aimed at studying the phytochemical and morphological variability of two populations of Helichrysum from Elba Island, reported in the bibliography as belonging one to H. litoreum Guss. (population A) and H. italicum subsp. italicum (Roth) G. Don (population B). The specific aim of the experiment was to investigate the morphological and phytochemical characters discriminating between the two species. Twenty-one measured characters and 5 calculated variables were used in morphological analysis. Qualitative and quantitative phytochemistry was assessed focusing on the occurrence and relative concentration of monoterpenes and sesquiterpenes. The results suggest that morphological discriminant traits were mainly in leaves and cypselae glandular tissues. Phytochemical analysis indicated that a high relative content of α-pinene and β-caryophyllene were the main markers for population A, while a high relative content of neryl acetate, α-curcumene, isoitalicene and italicene, especially in the terpene profile of bark tissue, were the main compounds for discriminating population B. Although, the analysis suggested that the wild population A could be mainly ascribed to H. litoreum, whilst population B could be identified as H. italicum subsp. italicum a more detailed morphological and genetic study is necessary. For this reason, I have conducted a second experiment aimed to investigate the morphological and genetic variability of Helichrysum in 12 wild populations growing on the Elba, Capraia and Giglio Islands. Morphological analysis was carried out by using the same 21 measured traits and the 6 calculated variables, while genetic analysis was performed by means of 16 ISSR primers. The results showed high intra-population morphological variability, but low variability among populations. In general, genetic analysis pointed out a very low variability; most of this variability (86%) was detected within population. Both the high degree of morphological and genetic similarity and the lack of clear gaps in the pattern of variation cannot allow to justify the identification of more than one species. Based on these findings, the occurrence of H. italicum subsp. italicum in the Tuscan Archipelago seems more likely than H. litoreum. The different number of samples considered and the lack of reference samples from the loci classici and herbarium specimens in the first study could partially explain the observed discordance of the results obtained from these two studies. Moreover, some studies have reported that H. italicum subsp. italicum and H. litoreum can be considered as part of the same taxonomic complex and that hybridization and introgression between them are rather common. The aim of the third experiment was to investigate the terpene variability of the 12 H. italicum subsp. italicum populations both at intra- and inter-populations levels. Although analysis of the terpene profile showed a high intra-population variation, on average the individuals of the same population were chemically more similar to each other than they were to the individuals of the other populations. Two main chemotypes were found: at high neryl acetate content the one and at high a-pinene content the other. Spearman correlation analysis showed differences in terpene composition in Elba populations collected at different altitudes (from the seaside to the low mountain) confirming that some environmental factors associated with the altitudinal gradient (e.g., temperature, rainfall, evapotranspiration, lithological substrate) can influence the terpene production. Similar altitudinal trends were observed in other studies for Croatia and Sardinia. Finally, a preliminary evaluation of the wild populations cultivated under common garden conditions was carried out in order to investigate the qualitative-quantitative properties of the essential oil extracted from the 12 H. italicum subsp. italicum populations, and to analyse possible differences in terpene composition between wild and cultivated plants. A comparison between wild and cultivated genotypes was also carried out to evaluate the influence of the different environmental conditions on glandular trichome density. The results obtained were promising, as the essential oil of the populations had a neryl acetate and a-pinene contents very similar to those found for the same populations growing in their natural habitats, demonstrating a probable genetic influence on the production of these metabolites. Moreover, this analysis allowed to find a correlation between glandular tricome density of the leaf abaxial surface and the essential oil yield.