This work investigated the structural and biochemical changes during grape berry development which account potentially for the onset and increase in susceptibility to Botrytis cinerea. Using the cv. Sauvignon blanc, we quantified at seven developmental growth stages from herbaceous to over-mature berries: (1) fruit ontogenic resistance using three strains (II-transposa), (2) the morphological and maturity fruit characteristics and (3) preformed biochemical compounds located in the berry skin. From the mid-colour change stage onwards, susceptibility of unwounded fruit increased sigmoidally in both rot and sporulation severities at the berry surface. A principal component analysis identified a very close connection between fruit susceptibility and the level of fruit maturity. Berry susceptibility was significantly and positively correlated with the phenolic compounds in the skin cell walls and negatively correlated with the total tannin content in the skin and with water activity (Aw) at the fruit surface. On the berry, Aw decreased from 0.94 at bunch closure to 0.89 at berry maturity, with a relatively low value (0.90) at the stage of mid-colour change. Using artificial media, different Aw levels led to significant differences in mycelial growth (Aw ≤0.95 resulted in the lowest growth rate ≤0.34 mm day −1 ). Thus, besides the level of fruit maturity, both water activity on the fruit and the total tannin content in the skin may affect fungal growth and berry colonisation. The potential of these variables for use as indicators of grape berry susceptibility as well as associated mechanisms for the development of disease are discussed.

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<p style="text-align: justify;">Grape berry ripening is characterised by numerous metabolic and physiological changes, placed under hormonal control. The phytohormone abscisic acid (ABA) is considered as a possible promoter of « véraison », since it accumulates at this time. In order to evaluate its impact, we assess the effect of ABA on several parameters of maturity: anthocyanins synthesis, phenylalanine ammonia-lyase activity, sugar contents, acidity and maturity index, both in untreated berry skin and in skin of berries submitted to applications of exogenous ABA. The maturation processes we focused on appear ABA-dependent, as they occured immediately after ABA accumulation in the skin. Treatment also shows a close relationship between ABA and the beginning of ripening. These results allow us to conclude that ABA content could modulate the triggering of « véraison ».</p>

Aims:The objective was to better understand the mechanisms involved in grape ripening that brings about important changes in the physiology and chemistry of the fruit. So we focused on the involvement of two growth regulators: abscisic acid (ABA) and indol-acetic acid (IAA) in controlling grape berry ripening process Methods and results:We described the evolution of the two plant growth regulators during the development of cv. Merlot grapes (Vitis vinifera L.). In order to better understand the role of ABA and IAA in the ripening control, these two growth regulators were applied on the grapes at the onset of veraison. The hormonal profile was established on treated berries and different physiological parameters were assayed to evaluate the effects of both applications. The partitioning of both plant growth regulators in nontreated berries showed that ABA and IAA accumulated at the onset of ripening. Moreover, it appeared that endogenous ABA decreased progressively in the flesh while accumulated in the skin from the beginning of the colour change to maturity. The hormonal treatments modified the hormonal profile and several physiological parameters: sugar, acidity, colour, and Botrytis sensibility. Conclusion:These findings suggest that both treatments have modified the ripening process. Exogenous ABA has induced advancement in grape ripening, while IAA application has delayed this process. These observations support the view that the grape ripening process may be influenced by the hormonal status.Significance and impact of study: This study gives new information about the ripening control of the non-climacteric fruits. In grape berries, it provides evidence of a possible co-involvement of ABA and IAA in controlling ripening process.Key words: abscisic acid, indol-acetic acid, hormonal balance, grape berry ripening, Vitis vinifera L.Objectif : L'objectif est de mieux appréhender les mécanismes impliqués dans la maturation de la baie de raisin, qui provoquent de profonds changements physiologiques et chimiques du fruit. Ainsi, nous nous sommes intéressés à l'implication de deux régulateurs de croissance : l'acide abscissique (ABA) et l'acide indole acétique (AIA) dans le contrôle du processus de maturation des baies.Méthodes and résultats : L'évolution de ces deux régulateurs de croissance a été suivi au cours du développement de baies de cépage Merlot (Vitis vinifera L.). Pour mieux comprendre le rôle de l'ABA et de l'AIA dans le processus de maturation, ces deux régulateurs de croissances ont été appliqués sur les baies au moment du déclenchement de la véraison. Le profil hormonal a été établi sur les baies traitées et différents paramètres physiologiques ont été testés afin d'évaluer les effets de ces deux applications. La répartition des deux régulateurs de croissance dans les baies non traitées montre que l'ABA et l'AIA s'accumulent au début de la véraison. De plus, il apparaît que les teneurs en ABA endogène diminuent progressivement dans la pulpe alors qu'elles s'accumulent dans la pellicule du début vérais...