Physiological and developmental disturbances caused by Botryosphaeria dieback in the annual stems of grapevine.

Botryosphaeria dieback is a grapevine trunk disease caused by fungi of the Botryosphaeriaceae family, which attacks more specifically the woody tissues. The infection leads to different symptoms including a severe form with a leaf drop as well as premature plant death. Botryosphaeria dieback causes major economic losses, since no effective treatment is yet available. A better understanding is necessary to find solutions to fight this disease. In this study, our objective was to characterize the "leaf drop" form by (1) looking for the presence of pathogens in the basal internodes of stems, (2) quantifying blocked vessels by tylosis and/or gummosis, and (3) describing the impact of the disease on vine physiology (gene expression and metabolome) and development (establishment and functioning of the cambium and phellogen) at the level of xylem and phloem of basal stem internodes. Our study has shown that Botryosphaeriaceae were present in both phloem and xylem of the basal internodes of the annual stem, with xylem vessels obturated. We have also clearly demonstrated that gene expression and metabolite profiles were strongly modified in both xylem and phloem of diseased plants. Differences in stems between healthy (control, C) and diseased (D) plants were low at flowering (vines not yet symptomatic), higher at the onset of symptom expression and still present, although less marked, at full disease expression. qRT-PCR analysis showed in both phloem and xylem an overexpression of genes involved in plant defense, and a repression of genes related to meristematic activity (i.e. vascular cambium and phellogen). Metabolomic analysis showed specific fingerprints in stems of healthy and diseased plants from the onset of symptom expression, with an increase of the level of phytoalexins and mannitol, and a decrease of 1-kestose one. At the structural level, many alterations were observed in internodes, even before the onset of symptoms: a classical obstruction of xylem vessels and, for the first time, a disorganization of the secondary phloem with an obstruction of the sieve plates by callose. The disease modifies the development of both secondary phloem (liber) and phellogen. Altogether, this study combining different approaches allowed to highlight deep vine dysfunction in the internodes at the base of stems, that may explain vine decline due to Botryosphaeria dieback.

Esca-affected grapevine leaf metabolome is clone- and vintage-dependent.

Esca is a complex grapevine trunk disease caused by wood-rotting ascomycetes and basidiomycetes and leading to several foliar and wood symptoms. Given that the esca expression can be influenced by several environmental, physiological, and genetic factors, foliar symptoms are inconsistent in incidence and prevalence and may appear 1 year but not the following. We have previously reported a clone-dependent expression of the disease in cv Chardonnay. Owing to metabolome analysis, we could discriminate the metabolite fingerprint of green leaves collected on diseased vines of clones 76 and 95. These clone-dependent fingerprints were year-dependent in intensity and nature. The present work was conducted to determine if the clone-dependent disease expression observed is specific to Chardonnay or if it also occurs in another cultivar. A plot located in the Jura vineyard (France) and planted with both 1004 and 1026 clones of Trousseau, a cultivar highly susceptible to esca, was thus selected and studied during 2017 and 2018. A year-dependent variation of the symptoms expression was first observed and a possible relationship with rainfall is hypothesized and discussed. Moreover, a higher percentage of the clone 1026 vines expressed disease, compared to the 1004 ones, suggesting the higher susceptibility of this clone. Finally, metabolomic analyses of the remaining green leaves (i.e, without symptom expression) of partial esca-apoplectic vines allowed us to confirm a clone-dependent metabolic response to the disease. The metabolite fingerprints obtained differed in nature and intensity to those previously reported for Chardonnay and also between years.

Clone-Dependent Expression of Esca Disease Revealed by Leaf Metabolite Analysis.

Grapevine trutk diseases, especially Esca, are of major concern since they gradually alter vineyards worldwide and cause heavy economic losses. The expression of Esca disease symptoms depends on several factors, including the grapevine cultivar. In this context, a possible clone-dependent expression of the Esca disease was studied. Two clones of 'Chardonnay' grown in the same plot were compared according to their developmental and physiological traits, metabolome, and foliar symptom expression. Analysis of their leaf metabolome highlighted differences related to symptom expression. Interestingly, the content of a few specific metabolites exhibited opposite variations in leaves of symptomatic shoots of clones 76 and 95. Altogether this study showed a clone-dependent expression of Esca disease in 'Chardonnay' and the relevance of GC-MS and 3D fluorescence methods to analyze the impact of the disease on the leaf metabolome.