Physiologie Pathologie et Génétique Végétales

Abstract Although ozone (O3) is a well‐known bactericide and fungicide, the required dose of ozone can depend significantly on the targeted pathogens. The present research evaluates the variation in sensibility to ozone of three fungal species from a single fungal group. The three fungal species selected, Venturia inaequalis, Botrytis cinerea, and Neofabreae alba, belong to the Ascomycota group and attack apples. The fungi were exposed to ozone by bubbling directly into the spore solutions (treatment period ranged from 0.5 to 4 min, ozone concentration in inlet gas ranged from 1 to 30 g/m3). The rates of germination were determined, and the level of peroxidation of the lipid membrane was quantified based on the malondialdehyde (MDA) production. The results indicate that ozone effectively reduces spore development and suggest that the fungi differ in sensitivity. To reduce by 50% the spore germination rate of N. alba, B. cinerea, and V. inaequalis requires ozone doses of 0.01, 0.03, and 0.07 mg/ml, respectively. Spore sensitivity seems to be directly linked to spore surface. For all the fungal species, the MDA level and the level of spore inactivation both increase with ozone dose, which confirms that ozone alters the cell membrane.

Trunk diseases are factors that limit sustainability of vineyards worldwide. Botryosphaeria and Eutypa diebacks are caused by several fungi belonging to the Botryosphaeriaceae and Diatrypaceae, respectively, with Diplodia seriata and Eutypa lata being two of the most common species. Previous information indicated that the traditional isolation method used to detect these pathogens from plant samples could underestimate their incidence levels. In the present study, we designed two sets of primers that target the β-tubulin gene and that are amenable for quantitative real-time PCR (qPCR) Sybr-Green assays for the detection and quantification of D. seriata-complex (DseCQF/R) and E. lata (ElQF/R) DNA. The design of a species-specific assay was achieved for E. lata. For D. seriata, a species-specific assay could not be designed. The low interspecific diversity across β-tubulin genes resulted in an assay that could not discriminate D. seriata from some closely related species either not yet reported or presenting a low prevalence on grapevine, such as D. intermedia. We validated our technique on grapevine spur samples naturally and artificially infected with D. seriata and E. lata during the dormant season. Experimental grapevines were located in two counties of northern California where the incidence of both pathogens was previously reported. The qPCR assays revealed that a high frequency of pruning wound infections (65%) was achieved naturally by E. lata, while low infection frequency (less than 5%) was observed using the reisolation method. For D. seriata-complex, low (5%) to no natural infection frequencies were observed by the qPCR and the reisolation method, respectively. These results also provided evidence that our qPCR detection methods were more sensitive to assess the incidence of E. lata and D. seriata-complex in plant samples, than traditional isolation techniques. Benefits of molecular methods for the detection of canker pathogens in the field under natural conditions are discussed.

ABSTRACT Selection pressure impacts genomes unevenly, as different genes adapt with differential speed to establish an organism’s optimal fitness. Plant pathogens co-evolve with their hosts, which implies continuously adaption to evade host immunity. Effectors are secreted proteins that mediate immunity evasion, but may also typically become recognized by host immune receptors. To facilitate effector repertoire alterations, in many pathogens, effector genes reside in dynamic genomic regions that are thought to display accelerated evolution, a phenomenon that is captured by the two-speed genome hypothesis. The genome of the vascular wilt pathogen Verticillium dahliae has been proposed to obey to a similar two-speed regime with dynamic, lineage-specific regions that are characterized by genomic rearrangements, increased transposable element activity and enrichment in in planta -induced effector genes. However, little is known of the origin of, and sequence diversification within, these lineage-specific regions. Based on comparative genomics among Verticillium spp. we now show differential sequence divergence between core and lineage-specific genomic regions of V. dahliae . Surprisingly, we observed that lineage-specific regions display markedly increased sequence conservation. Since single nucleotide diversity is reduced in these regions, host adaptation seems to be merely achieved through presence/absence polymorphisms. Increased sequence conservation of genomic regions important for pathogenicity is an unprecedented finding for filamentous plant pathogens and signifies the diversity of genomic dynamics in host-pathogen co-evolution.

Rotundone, the main aroma compound responsible for peppery notes in red wine, has a strong affinity with solids and may be affected by wine fining. This work aimed to study the impact of several fining agents on this compound using a red wine made from Tardif. Egg albumin, gelatine, vegetable protein (pea protein) and sodium bentonite were investigated at the same dosage (D1, 20 g/hL) to compare their effect under similar conditions and at a second dosage, which corresponds, depending on the agents, either to half of D1 or twice D1 to reflect more common winemaking practices. Overall, the fining agents had a minor, although significant effect on rotundone, with the greatest impact, which might not be detectable sensorily speaking, observed for vegetable protein (pea protein) used at 40 g/hL (–12.1 %). At D1, although not statistically different from gelatine and vegetable protein (pea protein), egg albumin induced the largest decrease in rotundone, which could be attributable to its higher surface charge density. A correlation (R2 = 0.85) was noticed between mean values of rotundone concentrations (3 replicates) and A620, suggesting that this proxy can be used to predict the impact of fining on rotundone in Tardif red wines. Though further work is necessary to investigate the impact of additional fining agents and to better understand the mechanisms involved, notably using computational chemistry, our results encourage winemakers to use fining agents in their wine if required, without having to fear excessive rotundone losses.

The increasing development of disease-resistant hybrid grape varieties requires rapid analytical approaches to assess their aroma potential. Conventional methods used to quantify glycosidic aroma precursors rely on laborious extraction procedures and GC–MS analyses. In this study, Selected Ion Flow Tube Mass Spectrometry (SIFT-MS), a high-throughput headspace analysis technique, was evaluated as a rapid volatilome fingerprinting tool to screen the aroma precursor potential of grape varieties. Thirty-three samples of red Vitis vinifera and hybrid frozen berries were thawed, homogenized in tartrate buffer (pH 5.5), incubated at 30°C for 15 h either without or with β-glycosidase, and analyzed by SIFT-MS using O 2 ⁺ as reagent ion. The volatilome showed clear clustering driven by enzymatic hydrolysis, highlighting the influence of glycosidic precursors on volatile signatures. A distinct cluster was observed for Clinton samples ( V. riparia × V. labrusca ). A classification and regression tree (CART) model developed from enzyme-treated samples showed promising ability to predict total glycosidic precursor content measured by GC–MS (R² = 0.94; RMSECV = 218 µg/L). Despite the limited influence of variety type, several low m/z ions enabled accurate sample classification and revealed diagnostic markers. These results highlight the potential of SIFT-MS as a rapid tool for screening aroma precursor potential in grapes. The proposed workflow reduces analytical turnaround to 18–20 hours per batch, compared with 2–3 days for conventional methods. As a trade-off between throughput and analytical certainty, it is compatible with the pace of harvest operations and large-scale variety phenotyping. It is potentially transposable to other plant matrices in which glycosidic precursors play a role in flavor development.