Vitis Methods to Understand and Develop Strategies for Diagnosis and Sustainable Control of Grapevine Trunk Diseases.

Vitis vinifera is affected by many diseases every year, depending on causal agents, susceptibility of cultivars, and climate region. Some are caused by a single agent, such as gray mold caused by Botrytis cinerea or powdery mildew caused by Erysiphe necator. Others result from the actions of a complex of pathogens such as grapevine trunk diseases (GTDs). GTDs are presently among the most devastating diseases in viticulture worldwide because both the economic losses and the long-term sustainability of vineyards are strongly affected. The complexity of GTDs results from the diversity of associated fungi, the undetermined period of latency within the vine (asymptomatic status), the erratic foliar symptom expression from one year to the next, and, probably correlated with all of these points, the lack of efficient strategies to control them. Distinct methods can be beneficial to improve our knowledge of GTDs. In vitro bioassays with cell suspensions, calli, foliar discs, full leaves, or plantlets, and in vivo natural bioassays with cuttings, grafted plants in the greenhouse, or artificially infected ones in the vineyard, can be applied by using progressive integrative levels of in vitro and in vivo, depending on the information searched. In this review, the methods available to understand GTDs are described in terms of experimental procedures, main obtained results, and deliverable prospects. The advantages and disadvantages of each model are also discussed.

Grapevine trunk diseases under thermal and water stresses.

MAIN CONCLUSION: Heat and water stresses, individually or combined, affect both the plant (development, physiology, and production) and the pathogens (growth, morphology, dissemination, distribution, and virulence). The grapevine response to combined abiotic and biotic stresses is complex and cannot be inferred from the response to each single stress. Several factors might impact the response and the recovery of the grapevine, such as the intensity, duration, and timing of the stresses. In the heat/water stress-GTDs-grapevine interaction, the nature of the pathogens, and the host, i.e., the nature of the rootstock, the cultivar and the clone, has a great importance. This review highlights the lack of studies investigating the response to combined stresses, in particular molecular studies, and the misreading of the relationship between rootstock and scion in the relationship GTDs/abiotic stresses. Grapevine trunk diseases (GTDs) are one of the biggest threats to vineyard sustainability in the next 30 years. Although many treatments and practices are used to manage GTDs, there has been an increase in the prevalence of these diseases due to several factors such as vineyard intensification, aging vineyards, or nursery practices. The ban of efficient treatments, i.e., sodium arsenite, carbendazim, and benomyl, in the early 2000s may be partly responsible for the fast spread of these diseases. However, GTD-associated fungi can act as endophytes for several years on, or inside the vine until the appearance of the first symptoms. This prompted several researchers to hypothesise that abiotic conditions, especially thermal and water stresses, were involved in the initiation of GTD symptoms. Unfortunately, the frequency of these abiotic conditions occurring is likely to increase according to the recent consensus scenario of climate change, especially in wine-growing areas. In this article, following a review on the impact of combined thermal and water stresses on grapevine physiology, we will examine (1) how this combination of stresses might influence the lifestyle of GTD pathogens, (2) learnings from grapevine field experiments and modelling aiming at studying biotic and abiotic stresses, and (3) what mechanistic concepts can be used to explain how these stresses might affect the grapevine plant status.

Diaporthe diversity and pathogenicity revealed from a broad survey of grapevine diseases in Europe.

Species of Diaporthe are considered important plant pathogens, saprobes, and endophytes on a wide range of plant hosts. Several species are well-known on grapevines, either as agents of pre- or post-harvest infections, including Phomopsis cane and leaf spot, cane bleaching, swelling arm and trunk cankers. In this study we explore the occurrence, diversity and pathogenicity of Diaporthe spp. associated with Vitis vinifera in major grape production areas of Europe and Israel, focusing on nurseries and vineyards. Surveys were conducted in Croatia, Czech Republic, France, Hungary, Israel, Italy, Spain and the UK. A total of 175 Diaporthe strains were isolated from asymptomatic and symptomatic shoots, branches and trunks. A multi-locus phylogeny was established based on five genomic loci (ITS, tef1, cal, his3 and tub2), and the morphological characters of the isolates were determined. Preliminary pathogenicity tests were performed on green grapevine shoots with representative isolates. The most commonly isolated species were D. eres and D. ampelina. Four new Diaporthe species described here as D. bohemiae, D. celeris, D. hispaniae and D. hungariae were found associated with affected vines. Pathogenicity tests revealed D. baccae, D. celeris, D. hispaniae and D. hungariae as pathogens of grapevines. No symptoms were caused by D. bohemiae. This study represents the first report of D. ambigua and D. baccae on grapevines in Europe. The present study improves our understanding of the species associated with several disease symptoms on V. vinifera plants, and provides useful information for effective disease management.

Toxicity of extracellular proteins from Diplodia seriata and Neofusicoccum parvum involved in grapevine Botryosphaeria dieback.

Botryosphaeria dieback, esca and Eutypa dieback are three economic major grapevine trunk diseases that cause severe yield reduction in vineyards worldwide. The frequency of disease symptoms has increased considerably over the past decade, and no efficient treatment is currently available to control these diseases. The different fungi associated with grapevine trunk diseases mainly induce necrotic wood and characteristic foliar symptoms. In this context, fungi virulence factors and host invasion are not well understood. We hypothesise that extracellular proteins produced by Diplodia seriata and Neofusicoccum parvum, two causal agents associated with Botryosphaeria dieback, are virulence factors responsible for the pathogenicity. In our previous work, we demonstrated that the total extracellular compounds produced by N. parvum induced more necrosis on Chardonnay calli and triggered a different defence gene expression pattern than those produced by D. seriata. Furthermore, this aggressiveness was not clearly correlated with the production of mellein, a characteristic phytotoxin of Botryosphaeriaceae, in our in vitro calli model. To characterise other potential virulence factors and to understand the mechanisms of host invasion by the fungus, we evaluated the profile, quantity and the impact of extracellular proteins produced by these fungi on Vitis vinifera calli necrosis and defence gene expression. Our results reveal that, under the same conditions, N. parvum produces more extracellular proteins and in higher concentrations than D. seriata. With Vitis vinifera cv. Chardonnay cells, we showed that equivalent concentrations of proteins secreted by N. parvum were more aggressive than those of D. seriata in producing necrosis and that they clearly induced more grapevine defence genes.

Extracellular compounds produced by fungi associated with Botryosphaeria dieback induce differential defence gene expression patterns and necrosis in Vitis vinifera cv. Chardonnay cells.

Three major grapevine trunk diseases, esca, botryosphaeria dieback and eutypa dieback, pose important economic problems for vineyards worldwide, and currently, no efficient treatment is available to control these diseases. The different fungi associated with grapevine trunk diseases can be isolated in the necrotic wood, but not in the symptomatic leaves. Other factors seem to be responsible for the foliar symptoms and may represent the link between wood and foliar symptoms. One hypothesis is that the extracellular compounds produced by the fungi associated with grapevine trunk diseases are responsible for pathogenicity.In the present work, we used Vitis vinifera cv. Chardonnay cells to test the aggressiveness of total extracellular compounds produced by Diplodia seriata and Neofusicoccum parvum, two causal agents associated with botryosphaeria dieback. Additionally, the toxicity of purified mellein, a characteristic toxin present in the extracellular compounds of Botryosphaeriaceae, was assessed.Our results show that the total extracellular compounds produced by N. parvum induce more necrosis on Chardonnay calli and induce a different defence gene expression pattern than those of D. seriata. Mellein was produced by both fungi in amounts proportional to its aggressiveness. However, when purified mellein was added to the culture medium of calli, only a delayed necrosis and a lower-level expression of defence genes were observed. Extracellular compounds seem to be involved in the pathogenicity of the fungi associated with botryosphaeria dieback. However, the doses of mellein used in this study are 100 times higher than those found in the liquid fungal cultures: therefore, the possible function of this toxin is discussed.