Cirillo, Aurora (2023) Climate change on olive physiology, on flower biology, on ripening of drupe and on olive oil quality. [Tesi di dottorato]

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Olive (Olea europaea L.) is one of the most important fruit trees of the Mediterranean region with an enormous economic, ecosystemic and environmental value and its growth and development are mainly affected by atmospheric conditions. In recent years, with the scenario of climate change, this species is being strongly exposed to thermal and hydric stresses during the growing season, mostly during summer. The changes in temperature and precipitation can negatively influence: the flower biology, the production, and quality of drupes and oil. For this reason, it is essential to adopt agronomic practices that allow better adaptability for drought and high temperatures. Among the traditional agronomic techniques to mitigate the effects of climate changes on plants there are soil management techniques which aim at containing water losses like the controlled water deficit techniques which lead to saving water resources. Over the past decade the application of biostimulants and anti-transpirants products as a sustainable practice to mitigate the negative impact of environmental stresses and to ameliorate or maintain plant productivity has become increasingly widespread. The first aim of this research was to investigate the effects of different biostimulants classes like: Trichoderma, Micro-Algae, Seaweed and Glycine betaine (Chapter 2), and two anti-transpirants products such as Kaolin and Pinolene (Chapter 3) in order to mitigate the damages of high temperature and water stress conditions on young olive plants growing in greenhouse conditions. Subsequently, based on the results obtained in the two preliminary studies (mentioned above), we tested some of the pervious biostimulants in open field conditions to observe their effects on the quantitative-qualitative parameters of the drupes and oil of a native Campania cultivar "Racioppella" (Chapter 4). The results obtained from these studies have shown the efficiency in the use of biostimulants and anti-transpirant products in improving biometric parameters of young olive trees, and qualitative and quantitative parameters of drupes and oil, in particular they improved fundamental parameters that determine the consumer satisfaction, as well as their antioxidant capacity and nutraceutical potential. The imminent climate changes in the Mediterranean areas, are rising concerns not only for gradual warming but also for extreme variations of seasonal temperatures. In fact, excessively hot springs influence the floral biology of plants, from the development of floral organs to pollination. Other solutions to mitigate climate changes consist in the selection of cultivars resistant or tolerant to high temperatures conditions during flowering and to clarify the physiological processes involved in heat-stress responses. A second aim of this study was to highlight possible differences among different olive cultivars in the time-course response of pollen viability to different combination of temperature and humidity treatments. We used pollen from 12 olive cultivars belonging to germplasm of the Campania region in Southern Italy and growing in the same site (Chapter 5). Most of the olive cultivars showed a significant decrease of pollen viability already after 24 h incubation under 36 °C and 100% RH. In a current scenario of climate change, it is critical to evaluate the effect of temperature on reproductive traits to predict the future impact of global warming on crop yield. Based on our results the cultivar that showed greater tolerance to extreme temperatures and humidity was “Biancolilla”, which could be used to survive in extreme environmental conditions. Altogether, results obtained in this thesis provide novel sustainable solutions to ameliorate and increase the yield of olive trees and the quality of their products,oil and drupes, under unfavorable environmental conditions.

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