Grasso, Filomena
(2015)
OLIVE GENETIC DIVERSITY AND MOLECULAR INTERACTION WITH BACTROCERA OLEAE.
[Tesi di dottorato]
Abstract
The worldwide interest in olive (Olea europaea L.) growing is due to the extraordinary nutritional and sensory quality of its main product: olive oil. From a nutritional point of view, extra virgin olive oil (EVOO) is the main lipid source of the so-called "Mediterranean diet", stated by the nutritionist Ancel Keys (Keys, 1970). Around 98% of the global table olives and olive oil is produced in the Mediterranean basin.Italy is the world's second largest exporter after Spain (European Commission, 2012).
Campania region has a long tradition in olive growing, with an overall production that represents 6.59% of national production (Carbonari and Sarnari, 2012). In spite of the rich olive and olive oil heritage of Campania region, until now a comprehensive genotyping study was still lacking. The first overall objective of the present thesis was to genotype twenty cultivars growing in Campania through 10 SSR markers. SSR fingerprinting allowed identification of a distinctive profile for all the studied varieties except 'Minucciola' and 'Nostrale', which did not display allelic differences. A widespread problem in classifying the 'Ravece' and 'Ortice' plants was pointed out. SSR analysis may contribute to eliminate the misidentification problem. The corresponding "monovarietal" EVOOs from each variety were then characterized for their fatty acid, biophenol composition and sensory profile. This study highlighted the possibility to characterize the 20 olive varieties from Campania on the basis of their FA composition (Diraman et al., 2010). Moreover, the analysis of biophenols sensory profile can give useful information to discriminate the EVOOs obtained from different olive varieties (de Medina et al., 2015; Tura et al., 2008). A low but significant correlation was found between olive SSR profiles and olive oil sensory profiles.
A determining factor on olive oil quality is represented by the plant interaction with its key enemy: the diptera Bactrocera oleae. The evolutionary history of the olive fly came along with that of Olea europaea, indicating an early and stable plant-insect association (Nardi et al., 2010). Despite global production of virgin olive oil and table olives is threatened by Bactrocera oleae, only few studies focused on Olea europaea molecular response to olive fly attack (Corrado et al., 2012; Alagna et al., 2015).
In this thesis a transcriptomic analysis was performed to achieve a more complete understanding of the molecular changes occurring once Bactrocera oleae attacks Olea europaea drupes. In order to explore the mechanisms that may trigger resistance to olive fly, two varieties were chosen with different levels of susceptibility to olive fly, namely 'Ruveia' and 'Ortice' (Pugliano et al., 2000). 'Ortice' and 'Ruveia' showed large differences in the mechanisms activated following the attack of the fly. The noticeable discrepancy in the number of the differentially expressed genes (FC > 2 and < 0.5; p-value < 0.05 Student's t-test) in the attacked olives of the two varieties, 52 in 'Ortice' and 2477 in 'Ruveia', indicates that the latter is able to activate a much broader response than the first as a result of the attack of the fly. The differentially expressed genes were recorded and discussed in ten functional categories concerning cellular organization, transcription, cell wall modification, stress and defense response, signal transduction, photosynthesis, primary metabolism, protein metabolism, secondary metabolism and transport.
On one hand, this thesis represents an advancement in the comprehension of the features characterizing olive oil quality in terms of variety and environment. On the other, an improvement in the knowledge of the interaction between olive and olive fly that largely influence olive production.
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