Fortes, Ana MargaridaMoore, John PaulSantos, Helena2024-05-242024-05-242024-012023-08http://hdl.handle.net/10451/64828Grapes are fruits highly susceptible to various diseases and stresses, including powdery mildew, esca disease, and grey mould. These conditions significantly impact grape quality, yield production, and aroma profiles. The infection strategy by the biotrophic fungus Erysiphe necator prioritises the development of appressoria for cell penetration of photosynthetic tissues using mechanical force, while the hemibiotrophic Botrytis cinerea secretes cell wall degrading enzymes to access the sugar-rich and ripe tissues. On the other hand, esca infects the grapevine trunk, leading to xylem destruction. The diverse responses of grapes to these different infection strategies often involve the cell wall, a critical component in grape development and defence that undergoes dynamic changes during different developmental stages and in response to pathogens. This thesis aims to investigate cell wall alterations in grapes, in the context of diverse fungal diseases, and their association with disease susceptibility, defensive responses, ontogenic resistance, and quality attributes. Grape cultivars were selected based on their susceptibility to the corresponding disease. Carignan exhibits high susceptibility to E. necator at the green stage, while more tolerant at veraison. Aragones (Tempranillo in Spain) is a cultivar susceptible to esca disease that exhibits either symptomatic or asymptomatic esca phenotypes in leaves, but often with limited symptoms in grapes. Trincadeira is highly susceptible to B. cinerea, as it displays infection symptoms from green to ripe, while Syrah, considered as tolerant to the fungus, shows symptoms mostly at the ripe stage. Two approaches were used, namely Gas Chromatography for the analysis of cell wall monosaccharide composition, and Comprehensive Microarray Polymer Profiling for cell wall polysaccharide evaluation. This provided a combined analysis of the putative grape cell wall architecture and composition during ripening and diseases incidence. These studies were complemented with transcriptional profiling regarding E. necator infection in grapes, and immunofluorescence studies with a xyloglucan-binding probe concerning Trincadeira and Syrah green grapes infected with B. cinerea. The cell wall studies on E. necator revealed significant differences in cell wall responses between green and veraison grapes. Results suggested increased callose levels and low degree of methylesterification in homogalacturonan in green grapes, while veraison grapes showed an increase in glucuronic acid. Regarding esca disease, grapes from symptomatic plants exhibited an increase in partially methylated homogalacturonan and a reduction in xyloglucans, mannans, and arabinogalactan proteins. Cultivar–specific differences in cell wall composition were observed in Trincadeira and Syrah samples, with higher abundance of arabinose and lower glucose in Syrah. Immunofluorescence images of Trincadeira grapes acquired using xyloglucan-binding probe displayed a putative B. cinerea infection, with intercellular hyphae development at the grape epidermis. These experiments highlight the diverse cell wall remodelling under different biotic stresses and reinforce its importance in grape defence strategies. The consequences of these diseases are most notable in the impact in grape aroma components, ranging from new compounds or content changes in certain compounds synthesised by the plant, to the release of fungal metabolites with off-flavours. Hence, this thesis also aimed to investigate the volatile organic compounds profile of Trincadeira, a cultivar classified as non-aromatic, and its changes under infection with B. cinerea. Headspace-–SPME Gas Chromatography was used for the analysis, identifying various volatile organic compounds, including alcohols, ester acetates, and fatty acid esters. Significant differences in volatile composition were observed between healthy and infected grapes, indicating amyl alcohol and 2-trans-hexenal as putative markers of infection, and providing insights into the impact of B. cinerea on grape quality and health. In conclusion, this comprehensive thesis contributes to decipher the pivotal role of the grape cell wall in response to various fungal diseases. These investigations into cell wall alterations contribute to a deeper understanding of the intricate interplay between the grape cell wall and biotic stresses, ultimately paving the way for the development of innovative strategies to enhance grapevine health, grape quality (with preserved aroma), and overall resilience against pathogens.engVitis viniferaamadurecimentodoenças fúngicasaromaparede celularVitis vinifera grapesripeningfungal diseasescell Walldoctoral thesis101642490