Construction of A High-Density Genetic Map And Detection of A Major QTL of Resistance To Powdery Mildew (Erysiphe Necator Sch.) In Caucasian Grapes (Vitis Vinifera L.)

Abstract

BackgroundVitis vinifera L. is the most cultivated grapevine species worldwide. Erysiphe necator Sch., the causal agent of grape powdery mildew, is one of the main pathogens affecting viticulture. V. vinifera has little or no genetic resistance against E. necator and the grape industry is highly dependent on agrochemicals. Some Caucasian V. vinifera accessions have been reported to be resistant to E. necator and to have no genetic relationship to known sources of resistance to powdery mildew. The main purpose of this work was the study and mapping of the resistance to E. necator in the Caucasian grapes ‘Shavtsitska’ and ‘Tskhvedianis tetra’.ResultsThe Caucasian varieties ‘Shavtsitska’ and ‘Tskhvedianis tetra’ showed a strong partial resistance to E. necator which segregated in two cross populations: the resistant genotypes delayed and limited the pathogen mycelium growth, sporulation intensity and number of conidia generated. A total of 184 seedlings of ‘Shavtsitska’ x ‘Glera’ population were genotyped through the Genotyping by Sequencing (GBS) technology and two high-density linkage maps were developed for the cross parents. The QTL analysis revealed a major resistance locus, explaining up to 80.15% of the phenotypic variance, on ‘Shavtsitska’ linkage group 13, which was associated with a reduced pathogen infection as well as an enhanced plant necrotic response. The genotyping of 105 Caucasian accessions with SSR markers flanking the QTL revealed that the resistant haplotype of ‘Shavtsitska’ was shared by ‘Tskhvedianis tetra’ and a total of 24 Caucasian grape varieties, suggesting a widespread presence of this resistance in the surveyed germplasm. The uncovered QTL was mapped in the region where the Ren1 gene of resistance to E. necator, identified in the V. vinifera ‘Kishmish vatkana’ and related grapes of Central Asia, is located. The genetic analysis conducted revealed that the Caucasian grapes in this study exhibit a resistant haplotype different from that of Central Asian grape accessions.ConclusionsThe QTL isolated in ‘Shavtsitska’ and present in the Caucasian V. vinifera varieties could be a new candidate gene of resistance to E. necator to use in breeding programmes. It co-localizes with the Ren1 locus but shows a different haplotype from that of grapevines of Central Asia. We therefore consider this gene, named Ren1-2, a member of a cluster of R genes, of which the region is rich, and linked with, or possibly allelic, to the Ren1.

Phenotyping and genetic analysis of the Caucasian grape resistance toErysiphe necator

“…vatkana' -carrying Ren1), 'Johanniter' (carrying Ren3 and Ren9) and 'Cabernet sauvignon' ('Cabernet s.' -carrying no resistance loci) were produced by softwood cuttings and added to the experiments. The resistance to E. necator was studied by leaf discs bioassays in 2019 and 2020 prepared as described in Possamai et al (2021). An E. necator single spore isolate obtained from susceptible infected plants in the greenhouse in 2018 was maintained and multiplied every ten days on young and disinfected leaves of 'Cabernet s.' in Petri dishes.…”

“…A histochemical study was carried out and three leaf discs of 1 cm of diameter per individual were evaluated at 1, 2, and 3 days post infection (dpi) for several bioassays. Trypan-Blue staining was carried out as described in Possamai et al (2021). After Trypan-Blue staining, 1 cm discs were evaluated by bright-field microscopy (x100) and one-hundred germinated conidia per disc were categorized in 4 classes: 0 = conidia + appressoria; 1 = conidia + primary hypha; 2 = conidia + primary and secondary hypha; and 3 = conidia + three hyphae and/or branched hyphae.…”