Grapevine trunk diseases of cold-hardy varieties grown in Northern Midwest vineyards coincide with canker fungi and winter injury

A comparison of microbiota isolation methods reveals habitat preferences for fermentative yeasts and plant pathogenic fungi in the grape berry

The methodologies for profiling the grape berry microbiota have exponentially evolved in the past 25 years. Recently, concerns arose regarding the homogeneity in the protocols of grape harvesting, sequencing and bioinformatic analyses, but the bias introduced by the microbiota isolation method is still unexplored. This study followed a simple approach of comparing two most used methods of microbiota collection from grape berries (washing vs crushing), hypothesizing a significant impact in the outcome of the microbiota profiles analyzed by NGS metabarcoding. Experiments conducted in fruits of three cultivars of the Douro wine region showed that only 52 % of OTUs were common to both surface and juice microbiota, suggesting specific microbial niches. Thirteen fungal genera were abundantly detected in the fruit surface, including Alternaria, Aureobasidium, Cladosporium, Didymella and Bipolaris. Fermentative yeasts including Meyerozyma and Saccharomyces cerevisiae were exclusively detected in the juice, together with several Penicillium species. Distinct habitat preferences of species within the genera Alternaria, Sporobolomyces and Rhodotorula were also revealed. The study showed that the microbiota isolation method is crucial in the detection of certain plant pathogenic/saprophytic fungi and yeasts with biotechnological and oenological interest, adding novelty to the globally accepted assumption that S. cerevisiae in musts originates primarily from the cellar.

Hybrid Vitis Cultivars with American or Asian Ancestries Show Higher Tolerance towards Grapevine Trunk Diseases

Grape production worldwide is increasingly threatened by grapevine trunk diseases (GTDs). No grapevine cultivar is known to be entirely resistant to GTDs, but susceptibility varies greatly. To quantify these differences, four Hungarian grape germplasm collections containing 305 different cultivars were surveyed to determine the ratios of GTDs based on symptom expression and the proportion of plant loss within all GTD symptoms. The cultivars of monophyletic Vitis vinifera L. origin were amongst the most sensitive ones, and their sensitivity was significantly (p < 0.01) higher than that of the interspecific (hybrid) cultivars assessed, which are defined by the presence of Vitis species other than V. vinifera (e.g., V. labrusca L., V. rupestris Scheele, and V. amurensis Rupr.) in their pedigree. We conclude that the ancestral diversity of grapes confers a higher degree of resilience against GTDs.

Fungal species associated with grapevine trunk diseases in Washington wine grapes and California table grapes, with novelties in the genera Cadophora, Cytospora, and Sporocadus

Grapevine trunk diseases cause serious economic losses to grape growers worldwide. The identification of the causal fungi is critical to implementing appropriate management strategies. Through a culture-based approach, we identified the fungal species composition associated with symptomatic grapevines from wine grapes in southeastern Washington and table grapes in the southern San Joaquin Valley of California, two regions with contrasting winter climates. Species were confirmed through molecular identification, sequencing two to six gene regions per isolate. Multilocus phylogenetic analyses were used to identify novel species. We identified 36 species from 112 isolates, with a combination of species that are new to science, are known causal fungi of grapevine trunk diseases, or are known causal fungi of diseases of other woody plants. The novel species Cadophora columbiana, Cytospora macropycnidia, Cytospora yakimana, and Sporocadus incarnatus are formally described and introduced, six species are newly reported from North America, and grape is reported as a new host for three species. Six species were shared between the two regions: Cytospora viticola, Diatrype stigma, Diplodia seriata, Kalmusia variispora, Phaeoacremonium minimum, and Phaeomoniella chlamydospora. Dominating the fungal community in Washington wine grape vineyards were species in the fungal families Diatrypaceae, Cytosporaceae and Sporocadaceae, whereas in California table grape vineyards, the dominant species were in the families Diatrypaceae, Togniniaceae, Phaeomoniellaceae and Hymenochaetaceae. Pathogenicity tests demonstrated that 10 isolates caused wood discoloration similar to symptomatic wood from which they were originally isolated. Growth rates at temperatures from 5 to 35°C of 10 isolates per region, suggest that adaptation to local climate might explain their distribution.