A single nucleotide polymorphism in the β-tubulin gene distinguishing two genotypes of Erysiphe necator expressing different symptoms on grapevine

The biotrophic fungus Erysiphe necator (formerly Uncinula necator ), for which two genetic groups have been described in European vineyards, is the causal agent of grapevine powdery mildew. By analysing the pathogen population with respect to polymorphism in the sequence of the β-tubulin gene, which distinguishes two groups of isolates, a new tool was developed for epidemiological and population studies and tested in the vineyard. As in many ascomycetes, the β-tubulin gene of E. necator ( Entub ) includes six introns and seven exons and encodes a 447-amino-acid protein. A single nucleotide polymorphism (SNP) in the intron-3 region of the Entub gene distinguished two genetic groups (A and B). This method was used to examine differences in the ratio of the two groups from a total of 289 grape powdery mildew samples collected at the beginning of the growing season from either flag shoots or leaves with sparse-spot symptoms in four different vineyards. The SNP in the intron-3 region of the β-tubulin gene, similar to SNPs in the CYP51 gene, was associated with genotypes A and B of E. necator and confirmed the existence of two sympatric populations of the pathogen in the French vineyards. Differences in the relative proportions of each group varied with the presence or absence of flag-shoot symptoms and with the region in which isolates had been collected.     

Effects of fungicide application on physiological and molecular responses of grapevine (Vitis vinifera L.): a comparison between copper and sulfur fungicides applied alone and in combination with novel fungicides

BACKGROUND

Chemical products against fungi and oomycetes pose serious environmental issues. In the last decade, the use of less impacting active ingredients was encouraged to reduce chemical inputs in viticulture. In this study, the effect of different antifungal compounds on grapevine agronomic, physiological, and molecular responses in the vineyard was evaluated in addition to protection against powdery and downy mildews.

RESULTS

In 2 years and in two Vitis vinifera cultivars (Nebbiolo and Arneis), a conventional crop protection approach, based on traditional fungicides (sulfur and copper), was compared to combined strategies. A well-known resistance inducer (potassium phosphonate), Bacillus pumilus strain QST 2808 and calcium oxide, both active ingredients whose biological interaction with grapevine is poorly characterized, were applied in the combined strategies in association with chemical fungicides. Despite a genotype effect occurred, all treatments optimally controlled powdery and downy mildews, with minimal variations in physiological and molecular responses. Gas exchange, chlorophyll content and photosystem II efficiency increased in treated plants at the end of season, along with a slight improvement in the agronomic performances, and an activation of molecular defense processes linked to stilbene and jasmonate pathways.

CONCLUSION

The disease control strategies based on potassium phosphonate, Bacillus pumilus strain QST 2808 or calcium oxide combined with traditional chemical compounds did not cause severe limitations in plant ecophysiology, grape quality, and productive yields. The combination of potassium phosphonate and calcium oxide with traditional fungicides can represent a valuable strategy for reducing copper and sulfur inputs in the vineyards, including those organically managed. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.