Ph. D. Elodie STEMPIEN

The study of the interaction between grapevine and Botryosphaeria dieback associated fungi: Understanding of induced defense mechanisms and factors of fungal aggressiveness

 

Thesis defended on July 13, 2017, in Colmar

Thesis co-supervision: Prof. Christophe Bertsch and Prof. Julie Chong

Abstract

Grapevine wood diseases, including Eutypa dieback, esca and Botryosphaeria dieback, are caused by complexes of fungi colonizing the xylem, and associated with different symptoms leading to plant death in the more or less long term. In the absence of efficient treatments, these diseases constitute a major problem for viticulture. Moreover, the factors involved in the progression and development of the disease are not yet fully identified.

In order to have a better understanding of B. dieback, we studied the molecular basis of interactions between grapevine and Botryosphaeriaceae, as well as the different virulence factors involved in the aggressiveness of these fungi. We studied the defense responses of grapevine induced by purified proteins secreted by Neofusicoccum parvum and Diplodia seriata, the two major fungi associated with B. dieback, using suspension cells of Vitis (Vitis rupestris and Vitis vinifera cv. Gewurztraminer) of different susceptibility. Then, we evaluated the wood-degrading enzymatic activities of N. parvum and D. seriata, and we also studied the ability of these fungi to metabolize the main phytoalexins of grapevine.

Our results show that Vitis cells are able to sense secreted proteins produced by Botryosphaeriaceae, resulting in rapid alkalinization of the extracellular medium and production of activated forms of oxygen. Proteins from N. parvum induce a more intense response compared to those from D. seriata. Early and late defense responses, i.e. alkalinization of the extracellular medium, cell death and expression of defense genes encoding PR proteins, are stronger in V. rupestris compared to V. vinifera, with the exception of stilbene production. The proteins secreted by Botryosphaeriaceae trigger a strong accumulation of δ-viniferin in V. vinifera suspension cells. Artificial inoculation tests of N. parvum and D. seriata on detached canes also showed that necrosis development was reduced in V. rupestris compared to V. vinifera cv. Gewurztraminer. This could be related to a more efficient and rapid induction of defense responses in V. rupestris, although not sufficient to completely inhibit fungal progression.

Furthermore, our results demonstrate that Botryosphaeriaceae are characterized by different wood-degrading enzymatic activities, and have the ability to rapidly degrade stilbenes. N. parvum is able to degrade parietal polysaccharides, whereas D. seriata has a better capacity to degrade lignin.