Abstract
The development of new resistant varieties to the oomycete Plasmopara viticola (Berk.& Curt) is a promising way to combat downy mildew (DM), one of the major diseases threatening the cultivated grapevine (Vitis vinifera L.). Taking advantage of a segregating population derived from “Merzling” (a mid-resistant hybrid) and “Teroldego” (a susceptible landrace), 136 F1 individuals were characterized by combining genetic, phenotypic, and gene expression data to elucidate the genetic basis of DM resistance and polyphenol biosynthesis upon P. viticola infection. An improved consensus linkage map was obtained by scoring 192 microsatellite markers. The progeny were screened for DM resistance and production of 42 polyphenols. QTL mapping showed that DM resistance is associated with the herein named Rpv3-3 specific haplotype and it identified 46 novel metabolic QTLs linked to 30 phenolics-related parameters. A list of the 95 most relevant candidate genes was generated by specifically exploring the stilbenoid-associated QTLs. Expression analysis of 11 genes in Rpv3-3+/− genotypes displaying disparity in DM resistance level and stilbenoid accumulation revealed significant new candidates for the genetic control of stilbenoid biosynthesis and oligomerization. These overall findings emphasized that DM resistance is likely mediated by the major Rpv3-3 haplotype and stilbenoid induction.
Highlights
Around 68,000 tons of fungicides per year are used in Europe to manage grape diseases, i.e., 65% of all fungicides used in agriculture viticulture encompasses only 4% of the EU arable land (Eurostat, 2007)
The Merzling” × “Teroldego” (M×T) genetic map built in this study is an improved version in terms of progeny individuals and linkage groups (LGs) number as well as marker number/order compared to the one by Salmaso et al (2008)
The high percentage of markers (68%) that was mapped in both parents is close to the 62% of markers positioned into the reference grapevine genetic map, while the 5% of distorted markers is about half of the value previously observed (Adam-Blondon et al, 2004)
Summary
Around 68,000 tons of fungicides per year are used in Europe to manage grape diseases, i.e., 65% of all fungicides used in agriculture viticulture encompasses only 4% of the EU arable land (Eurostat, 2007). A total of 27 Quantitative Trait Loci (QTLs) associated with DM resistance in different genetic backgrounds are known and described (VIVC, 2018). The major Rpv loci originated from Muscadinia rotundifolia (Merdinoglu et al, 2003), Vitis riparia (Marguerit et al, 2009; Moreira et al, 2011), V. amurensis (Blasi et al, 2011; Schwander et al, 2012; Venuti et al, 2013), V. cinerea (Ochssner et al, 2016), and V. rupestris (Divilov et al, 2018). The Rpv locus is a major determinant of grapevine DM resistance. Seven conserved Rpv haplotypes were identified in five descent groups of resistant varieties and traced back to their founders, which belong to V. rupestris, V. lincecumii, V. riparia, and V. labrusca (Di Gaspero et al, 2012). Until now only two haplotypes at this locus were validated in segregating populations derived from different DM resistance donors (Welter et al, 2007; Zyprian et al, 2016)
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