Selección y multiplicación de plantas aromático medicinales élite resistentes a sequía y de interés para la industria agroalimentaria

Resumo

Aromatic-medicinal plants (PAM), in addition to having great botanical and ecological interest due to their phylogenetic and floristic richness, represent one of the dryland crops of greatest interest for the food, cosmetics and pharmaceutical industries. However, they are possibly the great unknowns of Spanish agriculture, despite the fact that in our country and more specifically in the Region of Murcia, native species with great interest and commercial projection such as spike lavender and red thyme are cultivated. The production and demand for PAM have increased exponentially worldwide in recent years, not only due to its economic importance but also due to its possible use for the revaluation of non-urban land in disadvantaged rural areas. Both factors represent an essential stimulus for the development of improvement programs that help increase the viability of these crops. In this new scenario, one of the main threats facing global agriculture is the imminent climate change, which according to mathematical and statistical models, is expected to rise in the coming years, causing changes in global climate such as increased waves of heat and episodes of severe drought. Even though rainfed crops have mechanisms to counteract the negative effects of these adverse changes, drought is the most threatening environmental factor for agriculture, with a higher prevalence over time, which makes it a limiting factor for crop production in arid areas such as the Region of Murcia. Therefore, within PAM production improvement programs, it is important to include greater tolerance to drought as a selection factor to guarantee the sustainability of these productions. Based on this, the main objective of this thesis project focused on the need to select and multiply PAM ecotypes with greater resistance to water scarcity conditions, which allows for obtaining new varieties which be able to establish plantations with high yield and quality, typical of the area in which they are grown. As a starting point, for the establishment of homogeneous experimental plots, micropropagation protocols were developed for the mass production of genetically identical spike lavender and thyme plants. At the same time to obtain varieties resistant to drought, three different trials were prepared. In the first essay, “Evaluation of the physiological parameters in Lavandula latifolia Medik. under water deficit for preselection of elite drought-resistant plants” published in the journal Industrial Crops & Products, incipient spike lavender plants were subjected to two consecutive episodes of drought. Subsequently, clones of the surviving ecotypes (SL1 to SL8) were randomly assigned to two homogeneous groups. One group was irrigated at field capacity (as a control) and the other was subjected to water stress for two months. In the leaves of control and stressed plants, physiological parameters were measured, including relative water content (% RWC), water potential (ΨWP), proline, and abscisic acid. The next step was to compare the behavior in real growing conditions of drought-tolerant spike lavender versus two spike lavenders from a commercial crop. In the second essay, “Agronomic evaluation and chemical characterization of Lavandula latifolia Medik. under the semiarid conditions of the Spanish Southeast” published in the journal Plants, clones of the two preselected ecotypes were grown in an experimental plot, along with clones of two commercial plants (control). The main results confirmed an increase in biomass and essential oil production with plant age. The essential oil chemotype defined by 1,8-cineole, linalool and camphor was maintained over time, but a decrease in 1,8-cineole was detected in favor of linalool. In the phenolic profile, 14 components were identified, with salvianic acid and a derivative of rosmarinic acid being the main quantified compounds. These phenolic extracts showed a powerful antioxidant capacity in vitro, a characteristic that remained stable during the second and third year of cultivation. Finally, to obtain drought-resistant ecotypes of Thymus zygis ssp. gracilis, an excess of LED light was applied to generate a possible “memory” that allows an improvement in the response to severe drought. In the third experiment, “Physiological evaluation of Thymus zygis ssp. gracilis against drought, in ecotypes pretreated with high intensity LED light”, physiological parameters were evaluated, including relative water content and levels of proline and abscisic acid, content of photosynthetic pigments and tocochromanols, phenolic profiles, antioxidant capacity and lipid peroxidation in 1600 clones from 20 ecotypes. The results confirmed the negative effect of drought on the general condition of the plant, but also showed a positive effect of pretreatment with LED light, which improved the response of the antioxidant system in red thyme. Specifically, pretreatment with high light intensity was associated with a lower reduction in the content of photosynthetic pigments and tocochromanols, a higher content of caffeic acid dimethyl ether, and a reduction in lipid peroxidation in response to drought. Based on the previous results, it can be concluded that the intraspecific variability of L. latifolia in the response to drought can be considered a useful tool for the preselection of ecotypes with greater resistance to water stress, which, when evaluated in real field conditions, the crops reached a good level of production and yield after the second year of crop establishment. On the other hand, it was evident that a pretreatment with high light intensity could generate a possible "memory" that allowed T. zygis to overcome an episode of severe drought; Therefore, light stress could be considered as a useful technology for the selection of red thyme ecotypes with greater resistance to drought.