Cultivated grapevine (Vitis vinifera L.) is the world’s leading fruit crop for production and is grown in almost 90 countries mainly for wine production. This species is characterized by a phenotypic variability arises from the accumulation of gametic and somatic mutations during centuries of sexual and asexual propagation (Villano et al., 2022). For this reason, cultivars, local varieties, and related species represent a vast reservoir of traits/alleles that can be employed to improve the berry quality as well as the plant response against stresses.
Indeed, cultivated grapes are highly susceptible to diseases and in particular to PM, caused by the fungus Erysiphe necator. The reason for the grapevine susceptibility to PM can probably be reconducted to the different geographic origin of the plant (Eurasia) and the pathogen (North America). This hypothesis is also corroborated by the fact that wild North American vines are significantly more resistant to PM compared to the cultivated grape (Mullins et al., 1992). Nowadays, grapevine cultivation relies mainly on the applications of fungicides and on the set-up of vineyard management practices. However, the negative impact of chemicals on humans and agrobiodiversity has been widely demonstrated (Dry et al., 2019).
One strategy to shift from a treatment-oriented to a disease-prevention approach is by developing PM-resistant varieties (Rousseau et al., 2013). These ideotypes can be produced if the allelic configurations of a locus (or loci) related to PM resistance or susceptibility are known. To discover these loci, the use of segregating populations is a successful approach: in 2008, Hoffman et al. discovered a V. vinifera variety named “Kishmish vatkana” showing monogenic resistance to PM (Hoffmann et al., 2008).
Later, mildew resistances were subsequently described even from Vitis species from East Asia (reviewed by Vezzulli et al., 2022) and in Caucasian V. vinifera varieties (Possamai et al., 2022). Possamai et al. (2021) detected a major QTL located on chromosome 13 in a population obtained by crossing a Caucasian variety, ‘Shavtsitska’, carrying alleles conferring partial resistance to PM and the cultivar Glera (susceptible). Probably, the introgression of this trait in the domestication process was not intentional since no one reported PM disease in Europe and Asia before the 19th century. Instead, natural or intentional selection may have taken place after PM introduction from North America favouring the maintenance of the trait in the cultivated varieties.
Fischer et al. (2004) identified a QTL signal on chromosome 16 using a segregating population obtained from the cross of the resistant cultivar ‘Regent’ with the susceptible 'Lemberger'. A complementary approach is the detection of susceptibility genes, in this case the breeding selection is somehow easier due to the fact that no gene pyramiding is needed and the removal of the unfavourable (S-genes) allele will confer a durable and broad-spectrum resistance (Pavan et al., 2010).
The complex network of expression regulation active in grape after PM infection can be extended even to the post-transcriptional mechanisms and in particular to the microRNAs (miRNAs). They are non-coding RNAs of 20–24 nucleotides in length, that function as guide RNAs to direct the repression of their mRNA targets at post-transcriptional level. Some of these target genes include those involved in hormone signalling, responses to biotic and abiotic stresses (Pandita, 2022).
Poltronieri et al (2022) described a second line of defence based on small RNAs and RNA silencing, that is targeted by pathogen silencing suppressors, for this reason we will explore the miRNAs active in the infected grapes selected for high resistance and susceptibility through an integrated mRNA and miRNA omic analysis. Indeed, it has proven to be an effective method for exploring the molecular network at transcriptional and post-transcriptional levels because miRNAs recognize their mRNA targets via base pairing, and so the mRNA targets can be predicted using bioinformatics software.
Hence, DEMETRA is aimed at exploring the presence of resistance or susceptibility alleles as well as the post-transcriptional regulation system to provide an exhaustive overview of the genetic regulation of the resistance to PM that can be readily exploited in future breeding plans.
