Comprehensive analyses of the occurrence of a fungicide resistance marker and the genetic structure in Erysiphe necator populations.

Genetically distinct groups of Erysiphe necator, the fungus causing grapevine powdery mildew infect grapevine in Europe, yet the processes sustaining stable genetic differences between those groups are less understood. Genotyping of over 2000 field samples from six wine regions in Hungary collected between 2017 and 2019 was conducted to reveal E. necator genotypes and their possible differentiation. The demethylase inhibitor (DMI) fungicide resistance marker A495T was detected in all wine regions, in 16% of the samples. Its occurrence differed significantly among wine regions and grape cultivars, and sampling years, but it did not differ between DMI-treated and untreated fields. Multilocus sequence analyses of field samples and 59 in vitro maintained isolates revealed significant genetic differences among populations from distinct wine regions. We identified 14 E. necator genotypes, of which eight were previously unknown. In contrast to the previous concept of A and B groups, European E. necator populations should be considered genetically more complex. Isolation by geographic distance, growing season, and host variety influence the genetic structuring of E. necator, which should be considered both during diagnoses and when effective treatments are planned.

Paraffin oil induces resistance against powdery mildew in grapevine through salicylic acid signaling.

BACKGROUND: Mineral oils have been widely used in the pest control of several crops. However, their mode of action is poorly understood, especially in the case of their antifungal properties. The possible direct fungicidal activity and the stress-inducing capability of paraffin oil on grapevine were examined using Vitis vinifera L. cv 'Kékfrankos' cuttings and the fungus Erysiphe necator, the causal agent of powdery mildew. RESULTS: Our experiments demonstrated that paraffin oil does not have fungicide activity on E. necator, but induces significant stress-related changes in grapevine physiology. Elevated H2 O2 production and the accumulation of the phytohormone salicylic acid were measured. Secondary thickening of the cell wall by lignin deposition and the accumulation of phenolic compounds were also observed. Some enzyme activities related to the detoxification of reactive oxygen species, disease response, and the synthesis of lignin were changed in accordance with the determined changes in cell wall composition and H2 O2 levels. CONCLUSION: The results suggest that paraffin oil induces stress responses on grapevine leaves through oxidative burst, and this response is systemized by salicylic acid. The accumulation of lignin and water-soluble phenolics may be directly responsible for the paraffin oil-induced resistance of grapevine against powdery mildew. © 2021 Society of Chemical Industry.

Physico-Chemical Characteristics and Culturable Microbial Communities of Grape Berries Change Strongly during Noble Rot Development.

Botrytis cinerea is a well-known pathogen of grapevine. However, under certain microclimatic conditions, Botrytis infection results in noble rot, an essential process in the production of the world-known Tokaji aszú wines in Hungary. We investigated the physico-chemical characteristics and culturable microorganisms associated with grape berries through several noble rot phases in the two main cultivars grown in Tokaj: Vitisvinifera cv. "Furmint" and "Hárslevelu". We measured physical and analytical parameters routinely tested in viticulture and analyzed the ITS rDNA sequence data of fungi isolated from the sampled berries. We observed significant differences in the physico-chemical parameters among the noble rot phases as well as sampling dates. The greatest variation in berry texture and microbial structure was observed in the initial phases, with variables converging as the noble rot progressed. By finding a bijection between the examined chemical properties and the factorial parameters (e.g., noble rot phase, collection time, cultivar), an appropriate sweet winemaking material can be designed. Fungal community differed significantly among cultivars, with higher number of species observed in Hárslevelu. Our results reveal that there is more to noble rot than only Botrytiscinerea and other microorganisms may play important roles in the aszú process.