Pál Kozma

Historical Introgression of the Downy Mildew Resistance Gene Rpv12 from the Asian Species Vitis amurensis into Grapevine Varieties

The Amur grape (Vitis amurensis Rupr.) thrives naturally in cool climates of Northeast Asia. Resistance against the introduced pathogen Plasmopara viticola is common among wild ecotypes that were propagated from Manchuria into Chinese vineyards or collected by Soviet botanists in Siberia, and used for the introgression of resistance into wine grapes (Vitis vinifera L.). A QTL analysis revealed a dominant gene Rpv12 that explained 79% of the phenotypic variance for downy mildew resistance and was inherited independently of other resistance genes. A Mendelian component of resistance–a hypersensitive response in leaves challenged with P. viticola–was mapped in an interval of 0.2 cM containing an array of coiled-coil NB-LRR genes on chromosome 14. We sequenced 10-kb genic regions in the Rpv12+ haplotype and identified polymorphisms in 12 varieties of V. vinifera using next-generation sequencing. The combination of two SNPs in single-copy genes flanking the NB-LRR cluster distinguished the resistant haplotype from all others found in 200 accessions of V. vinifera, V. amurensis, and V. amurensis x V. vinifera crosses. The Rpv12+ haplotype is shared by 15 varieties, the most ancestral of which are the century-old ‘Zarja severa’ and ‘Michurinets’. Before this knowledge, the chromosome segment around Rpv12+ became introgressed, shortened, and pyramided with another downy mildew resistance gene from North American grapevines (Rpv3) only by phenotypic selection. Rpv12+ has an additive effect with Rpv3+ to protect vines against natural infections, and confers foliar resistance to strains that are virulent on Rpv3+ plants.

Rapid and multiregional adaptation to host partial resistance in a plant pathogenic oomycete: Evidence from European populations of Plasmopara viticola, the causal agent of grapevine downy mildew

Crop pathogens evolve rapidly to adapt to their hosts. The use of crops with quantitative disease resistance is expected to alter selection of pathogen life-history traits. This may result in differential adaptation of the pathogen to host cultivars and, sometimes, to the erosion of quantitative resistance. Here, we assessed the level of host adaptation in an oomycete plant pathogenic species. We analysed the phenotypic and genetic variability of 17 Plasmopara viticola isolates collected on Vitis vinifera and 35 isolates from partially resistant varieties (Regent and genotypes carrying the Rpv1 gene). Cross-inoculation experiments assessed two components of aggressiveness and a life-history trait of the pathogen: disease severity, sporangial production and sporangia size. The results contribute evidence to the emergence of P. viticola aggressive isolates presenting a high level of sporulation on the partially resistant Regent. By contrast, no adaptation to the Rpv1 gene was found in this study. The erosion of Regent resistance may have occurred in less than 5years and at least three times independently in three distant wine-producing areas. Populations from resistant varieties showed a significant increase in sporangia production capacity, indicating an absence of fitness costs for this adaptation. The increase in the number of sporangia was correlated with a reduction in sporangia size, a result which illustrates how partial plant disease resistance can impact selection of the pathogens life-history traits. This case study on grapevine downy mildew shows how new plant pathogen populations emerge in agro-ecosystems by adapting to partial host resistance. This adaptive pattern highlights the need for wise management of plant partial disease resistance to ensure its sustainability over time.

Selection for Run1-Ren1 Dihybrid Grapevines Using Microsatellite Markers

A grapevine hybrid progeny was generated to track the inheritance of the Ren1 and the Run1 powdery mildew resistance alleles and the segregation of the powdery mildew resistance phenotype. Genotypic analysis was carried out using flanking microsatellite markers; phenotypic evaluations were done under in vitro and greenhouse conditions. Pairing the phenotypic and genotypic data demonstrated that Ren1 and Run1 acted as single dominant loci and assorted independently without considerable distortion of segregation. Chromosomal recombination events were detected in the Ren1 but not in the Run1 region, corroborating earlier observations that crossover between homologous chromosomes was suppressed around the Run1 locus. Taken together, the results confirmed that microsatellite marker-assisted selection is a reliable and expeditious method to combine multiple alleles that confer resistance to a pathogen.

Differentiation of grapevine (Vitis vinifera L.) conculta members based on molecular tools

Twenty-seven grapevine (Vitis vinifera L.) varieties within 12 putative berry colour variation groups (conculta) were genotyped with 14 highly polymorphic microsatellite (simple sequence repeats (SSR)) markers. Three additional oligonucleotide primers were applied for the detection of the Gret1 retroelement insertion in the promoter region of VvMybA1 transcription factor gene regulating the UFGT (UDP-glucose: flavonoid 3-O-glucosyltransferase) activity. UFGT is the key enzyme of the anthocyanin biosynthetic pathway. SSR results proved that the analysed cultivars can be grouped only into nine concultas, the other three putative berry colour variant groups consist of homonyms as a consequence of misnaming. In the case of Sárfehér-Sárpiros, Delaware red-Delaware white and Járdovány fekete-Járdovány fehér, it was attested that they are not bud sports, but homonyms. Some conculta members could be differentiated according to the presence or the absence of the Gret1 retroelement (Chasselas, Furmint and Lisztes), while others, Bajor, Bakator, Gohér and Traminer conculta members, remained indistinguishable either by the microsatellites or the Gret1-based method.

An integrative AmpSeq platform for highly multiplexed marker-assisted pyramiding of grapevine powdery mildew resistance loci

Resistance breeding often requires the introgression and tracking of resistance loci from wild species into domesticated backgrounds, typically with the goal of pyramiding multiple resistance genes, to provide durable disease resistance to breeding selections and ultimately cultivars. While molecular markers are commonly used to facilitate these efforts, high genetic diversity and divergent marker technologies can complicate marker-assisted breeding strategies. Here, amplicon sequencing (AmpSeq) was used to integrate SNP markers with dominant presence/absence markers derived from genotyping-by-sequencing and other genotyping technologies, for the simultaneous tracking of five loci for resistance to grapevine powdery mildew. SNP haploblocks defined the loci for REN1, REN2 and REN3, which confer quantitative resistance phenotypes that are challenging to measure via field ratings of natural infections. Presence/absence markers for RUN1 and REN4 were validated to predict qualitative resistance phenotypes and corresponded with previous presence/absence fluorescent electrophoretic assays. Thus, 37 AmpSeq-derived markers were identified for the five loci, and markers for REN1, REN2, REN4 and RUN1 were used for multiplexed screening and selection within diverse breeding germplasm. Poor transferability of SNP markers indicated imperfect marker-trait association in some families. Together, AmpSeq SNP haploblocks and presence/absence markers provide a high-throughput, cost-effective tool to integrate divergent technologies for marker-assisted selection and genetic analysis of introgressed disease resistance loci in grapevine.

Marker assisted selection for seedlessness in a multiresistant table grape hybrid family

Resistant table grape cultivars, without any compromise in quality and resistance, would be greatly advantageous for consumers. In this study, the cross VRH 3082-1-42 × ?Kishmish moldvaskii? has been used to investigate the usefulness of the SSC8 marker for MAS. The SCC8 marker results were consistent with the progeny phenotypes. Although the seeded parent showed an unusual genotype, the genotyping of the population could be carried out. We traced back the haplotypes of the resistant donor parent. Based on our findings, the dominant, seedlessness-linked SCC8+ allele of the seeded VRH 3082-1-42 should be considered as a recombinant; the presence of a null allele could be explained by larger DNA rearrangements instead of mutations in the priming sites.