Two Neofusicoccumparvum isolates and a UV mutant were characterized for their phytotoxin production in vitro, their pathogenicity on grapevine, and their genome sequenced. The isolate Np-Bt67 produced high level of (-)-terremutin, but almost no (R)-mellein, and it was the most aggressive on grapevine, triggering apoplexy. Similar symptoms were not induced by purified (-)-terremutin. The isolate Bourgogne S-116 (Np-B) produced 3-fold less (-)-terremutin and high amounts of (R)-mellein, but it was less aggressive on grapevine than Np-Bt67. The UV9 mutant obtained from Np-B (NpB-UV9) no longer produced (-)-terremutin but overproduced (R)-mellein by 2.5-fold, and it was as pathogenic as its parent. NpB-UV9 differed from its parent by simple mutations in two genes (transcription factor UCR-NP2_6692, regulatory protein UCR-NP2_9007), not located neither near (R)-mellein, nor (-)-terremutin biosynthetic genes, but likely involved in the control of (-)-terremutin biosynthesis. Grapevine immunity was disturbed upon challenge with these pathogens or purified phytotoxins, leading to an upregulation of SA-dependent defenses, while (-)-terremutin interfered with host JA/ET-dependent defenses. Our results suggest that neither (-)-terremutin nor (R)-mellein alone is essential for the pathogenicity of N. parvum on grapevine, since isolate/mutant non-producing these toxins in vitro is pathogenic. However, these phytotoxins could play a quantitative role in the infection process.

Species from the Botryosphaeriaceae family are the causal agents of Botryosphaeria dieback (BD), a worldwide grapevine trunk disease. Because of their lifestyle and their adaptation to a wide range of temperatures, these fungi constitute a serious threat to vineyards and viticulture, especially in the actual context of climate change. Grapevine plants from both nurseries and vineyards are very susceptible to infections by botryosphaeriaceous fungi due to several cuts and wounds made during their propagation process and their entire life cycle, respectively. When decline becomes chronic or apoplectic, it reduces the longevity of the vineyard and affects the quality of the wine, leading to huge economic losses. Given the environmental impact of fungicides, and their short period of effectiveness in protecting pruning wounds, alternative strategies are being developed to fight BD fungal pathogens and limit their propagation. Among them, biological control has been recognized as a promising and sustainable alternative. However, there is still no effective strategy for combating this complex disease, conditioned by both fungal life traits and host tolerance traits, in relationships with the whole microbiome/microbiota. To provide sound guidance for an effective and sustainable integrated management of BD, by combining the limitation of infection risk, tolerant grapevine cultivars, and biological control, this review explores some of the factors conditioning the expression of BD in grapevine. Among them, the lifestyle of BD-associated pathogens, their pathogenicity factors, the cultivar traits of tolerance or susceptibility, and the biocontrol potential of Bacillus spp. and Trichoderma spp. are discussed.

Botryosphaeria dieback (BD) is a worldwide grapevine trunk disease constituting a serious threat to sustainable grapevine production, especially in the context of climate change. Effective treatments to control BD are still lacking, prompting the exploration of new non-chemical alternatives. Among these, biocontrol agents (BCAs), such as Trichoderma spp. and Bacillus spp., are described as promising. This study aimed to thoroughly investigate the physiological changes in grapevines induced by two BCAs, Bacillus subtilis ( Bs PTA-271) and Trichoderma atroviride ( Ta SC1), which are used to protect two cultivars from Neofusicoccum parvum Bt67 (Np-Bt67) infection. Using nontarget transcriptomic analysis (RNA-seq) and validation by qRT-PCR, this research offers novel insights into the molecular responses associated with Np-Bt67 infection in Chardonnay and Tempranillo cultivars in relation to the protective mechanisms conferred by each BCA. RNA-seq revealed that the cultivars showed no common transcriptional changes upon pathogen challenge. In Chardonnay, changes were mainly related to terpene/carotenoid pathways, whereas in Tempranillo, they mostly related to amino acid transport and photosynthesis. Following the inoculation of protective BCA, changes were also distinct between the infected cultivars: Bs PTA-271’s protective effect against infection in Chardonnay was mainly related to the phenylpropanoid pathway and secondary metabolic processes, whereas that of Ta SC1 for Tempranillo correlated with more metabolic changes. Consecutive validation by qRT-PCR provided markers indicating grapevine susceptibility versus protection against Np-Bt67, some of which are shared by both cultivars. These markers could offer valuable tools for monitoring the health status of grapevine toward N. parvum.