Berry Shrivel a physiological ripening disorder

The project Sugar metabolism and cell wall modification during the early induction of the grapevine physiological ripening disorder Berry Shrivel (BS) analyses the early changes during BS induction. The ripening disorder is of highly economic importance for winegrowers and especially in Austria the main red wine cultivar Zweigelt can show high incidence of BS in vineyards. The onset of BS induction starts at or short after Veraison, the start of grape berry ripening, and is leading to grapes of low quality with low sugar contents, high acidity, reduced anthocyanin content and strong off flavors. The processes and causes leading to BS induction and symptom development are still unclear. In the presented project we are following the hypothesis that BS is due to a reduced transport of assimilates towards grape berries. According to the current knowledge we are focusing on anatomical changes within the vascular system and we will establish an in vitro system to manipulate the carbohydrate support of single berries with the aim to artificially induce BS. Thereby different microscopic and molecular biological methods will be applied. Our approach is the first effort to analyze these early events during BS induction and will provide essential knowledge towards the unraveling of this complex ripening disorder affecting grape berries.

Within the project we analyzed the physiological ripening disorder berry shrivel (BS) from two different angles. Different microscopic techniques made changes within the vascular system of rachis and pedicels of BS affected grapes visible. Collapsed phloem cells as well as reduced cell layers within the cambium were observed. Additionally several sieve plates had callose depositions and the estimated sieve element conductivity was reduced up to 60%. These observed changes can reduce the transport of assimilates towards ripening berries. In a next step the actual transport flow within the phloem will have to be evaluated. On the basis of previous results, we also tested two hypothesis for artificial induction of BS: water logging and exogenous application of ethylene and ACC. A specific induction of BS would facilitate the scientific work with BS and would enable the sound validation of strategies to prevent BS. Unfortunately in both cases an induction of BS was not possible. The second focus of our project lay on the transcriptomic comparison of BS and healthy berries. A comprehensive RNA-sequencing and metabolites analyses on samples collected at six different developmental stages. During the ripening phase, more than 3000 genes are differentially expressed. Many genes are down-regulated and belong to a group of genes called SWITCH. The metabolites analysis, which mainly included major sugars determination and anthocyanins accumulation, revealed less amount of sugar and anthocyanin accumulation in the berry shrivel samples from veraison onward. This was in agreement with a down-regulation of the main genes involved in this two metabolic pathways. Unfortunately the mystery of BS induction could not be solved in the frame of the project, but our knowledge increased substantially and we identified promising approaches for follow up projects: the question of real time assimilate transport into grape berries and the role of SWITCH genes during BS induction and how they are influenced.