Grapevine trunk diseases (GTDs) are currently among the most important health challenges for viticulture in the world. Esca, Botryosphaeria dieback, and Eutypa dieback are the most current GTDs caused by fungi in mature vineyards. Their incidence has increased over the last two decades, mainly after the ban of sodium arsenate, carbendazim, and benomyl in the early 2000s. Since then, considerable efforts have been made to find alternative approaches to manage these diseases and limit their propagation. Biocontrol is a sustainable approach to fight against GTD-associated fungi and several microbiological control agents have been tested against at least one of the pathogens involved in these diseases. In this review, we provide an overview of the pathogens responsible, the various potential biocontrol microorganisms selected and used, and their origins, mechanisms of action, and efficiency in various experiments carried out in vitro, in greenhouses, and/or in vineyards. Lastly, we discuss the advantages and limitations of these approaches to protect grapevines against GTDs, as well as the future perspectives for their improvement.

Two major diseases that affect grapevine leaves and berries are controlled by the oomycete Pythium oligandrum. As the efficacy of biocontrol agents strongly depends on factors such as the trophic behaviors of pathogens and cultivar susceptibility, a two-disease approach was implemented to evaluate the activity of P. oligandrum against Botrytis cinerea (the necrotrophic fungus of gray mold) and Plasmopara viticola (the biotrophic oomycete of downy mildew) on two grapevine cultivars with different susceptibilities to these two pathogens. The results show that grapevine root inoculation with P. oligandrum significantly reduced P. viticola and B. cinerea infection on the leaves of the two cultivars, but with differences. This was observed when the relative expression of 10 genes was measured in response to each pathogen, and could be attributed to their lifestyles, i.e., biotrophic or necrotrophic, which are related to the activation of specific metabolic pathways of the plant. In response to P. viticola infection, genes from the jasmonate and ethylene pathways were mainly induced, whereas for B. cinerea, the genes induced were those of the ethylene–jasmonate pathway. The different levels of defense against B. cinerea and P. viticola could also explain the difference in cultivar susceptibility to these pathogens.

Grapevine trunk diseases (GTDs) are currently limiting grapevine productivity in many vineyards worldwide. As no chemical treatments are registered to control GTDs, biocontrol agents are being tested against these diseases. Esquive^® WP, based on the fungus Trichoderma atroviride I-1237 strain, is the first biocontrol product registered in France to control GTDs. In this study, we determine whether, following grapevine pruning wound treatments with Esquive^® WP, changes occurred or not in the indigenous microbial communities that are colonizing grapevine wood. Over a 6-year period, Esquive^® WP was applied annually to pruning wounds on three grapevine cultivars located in three different regions. Wood samples were collected at 2 and 10 months after the Esquive^® WP treatments. Based on MiSeq high-throughput sequencing analyses, the results showed that specific microbial communities were linked to each ‘region/cultivar’ pairing. In certain cases, a significant modification of alpha diversity indexes and the relative abundance of some microbial taxa were observed between treated and non-treated grapevines 2 months after Esquive^® WP treatment. However, these modifications disappeared over time, i.e., 10 months post-treatment. This result clearly showed that Esquive^® WP pruning wood treatment did not induce significant changes in the grapevine wood’s microbiome, even after 6 years of recurrent applications on the plants.

In recent studies, the bacterial and fungal communities associated with plant wood have received considerable attention. Due to microorganisms’ vertical migration from roots to leaves, these communities provide critical links between the rhizosphere and phyllosphere microbiome. Recent investigations have shown that anatomical and chemical wood characteristics shape the microbiota inhabiting living or dead wood tissues, leading to variation in the observed decomposition of these materials. Despite the fact that bacteria have limited ability to degrade polymeric lignocelluloses compared to fungi, those inhabiting wood tissues have demonstrated a significant role in these habitats. Bacteria and fungi coexist in wood and form differing relationships with each other, with consequences for community structures that, in turn, impact plant health. The aim of this review is to present an overview of current insights regarding bacterial profiles and functions in lignocellulosic plants and their interaction with fungal communities colonising the same habitat. A better understanding of plant–bacteria–fungi interactions will allow for better exploitation of these tripartite interactions and possibly improve plant health.