Ph. D. Clement LABOIS

Study of defense responses of Vitis vinifera subsp. sylvestris and fungal aggressiveness factors in grapevine wood diseases.

Defended on December 22, 2020, in videoconference due to sanitary crisis.

Thesis supervisor: Pr. Julie Chong, University of Haute Alsace

Thesis co-supervisor: PhD. Mary-Lorene GODDARD Research engineer, University of Haute Alsace

Abstract:

In recent years, vineyards in France and around the world have been confronted with an upsurge of wood diseases (WD) of grapevines. These diseases are the cause of yield and quality losses, but they are also responsible for an important mortality of the vines. Among these diseases, three main ones have been identified: esca (associated with a complex of fungi including Fomitiporia mediterraneae, Phaeoacremonium minimum and Phaemoniella chlamydospora), eutypiosis (caused by Eutypa lata) and Botryosphaeriaceae decline (associated with Botryosphaeriaceae subsp. including Neofusicoccum parvum (N. parvum) and Diplodia seriata (D. seriata)). Unfortunately, to date, there is no effective treatment to limit, protect and prevent these diseases. It has been shown in the laboratory that wild grapevine (sylvestris) is less susceptible to MDBs compared to cultivated grapevine (vinifera). To understand the differences in tolerance observed between wild and cultivated grapevine, we studied the variation in primary and specialized metabolism by HLPC-MS and GC-MS techniques. We also studied the activation of defense genes in response to N. parvum infection after inoculation of detached shoots by a transcriptomic study. In parallel to this work, we investigated the mechanisms of stilbene detoxification by the enzymatic arsenal of N. parvum and D. seriata fungi.

Our results show that N. parvum inoculation triggered significant changes in primary and specialized wood metabolism as well as differential expression of defense genes. In both subspecies, infection resulted in a strong decrease in sugars (fructose, glucose, sucrose), while the content of sugar alcohol (mannitol and arabitol) increased. Regarding amino acids, early infection with N. parvum triggered a decrease in aspartic acid, serine and asparagine, and a strong increase in alanine and β-alanine. We were able to observe a more rapid and intense alteration of primary metabolite levels in wild grapevine in response to infection compared with cultivated grapevine. The content of resveratrol and several resveratrol oligomers increased in the wood of both subspecies after infection. We could also observe an increase in the expression of several genes including STS, PPO and several GTS. We also observed a decrease in the expression of genes coding for ethylene biosynthesis and perception. It seems that the better tolerance of sylvestris to grapevine MDBs is due to the fact that this subspecies is able to initiate the induction or repression of certain defense genes more strongly, thus conferring a better defense against MDBs. Moreover, we have also shown that D. seriata and N. parvum were able to efficiently metabolize monomeric forms of stilbenes (resveratrol, pikeid and pikeatannol) to the benefit – and in a surprising way – of dimeric forms of stilbenes (in particular δ-viniferin, which is toxic to fungi) via extracellular enzymes.

In conclusion, our work shows a specificity of response of wild grapevine compared to cultivated grapevine with respect to the modification of primary and specialized metabolism. Our results also show the capacity of stilbenes detoxification by extracellular enzymes of fungi. These results could explain both the difference in susceptibility to MDBs observed between wild and cultivated grapevine but also how the fungi manage to get through the defenses put in place by the grapevine.