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.

The powdery mildew resistance gene REN1 co-segregates with an NBS-LRR gene cluster in two Central Asian grapevines.

BACKGROUND: Grape powdery mildew is caused by the North American native pathogen Erysiphe necator. Eurasian Vitis vinifera varieties were all believed to be susceptible. REN1 is the first resistance gene naturally found in cultivated plants of Vitis vinifera. RESULTS: REN1 is present in 'Kishmish vatkana' and 'Dzhandzhal kara', two grapevines documented in Central Asia since the 1920's. These cultivars have a second-degree relationship (half sibs, grandparent-grandchild, or avuncular), and share by descent the chromosome on which the resistance allele REN1 is located. The REN1 interval was restricted to 1.4 cM using 38 SSR markers distributed across the locus and the segregation of the resistance phenotype in two progenies of collectively 461 offspring, derived from either resistant parent. The boundary markers delimit a 1.4-Mbp sequence in the PN40024 reference genome, which contains 27 genes with known functions, 2 full-length coiled-coil NBS-LRR genes, and 9 NBS-LRR pseudogenes. In the REN1 locus of PN40024, NBS genes have proliferated through a mixture of segmental duplications, tandem gene duplications, and intragenic recombination between paralogues, indicating that the REN1 locus has been inherently prone to producing genetic variation. Three SSR markers co-segregate with REN1, the outer ones confining the 908-kb array of NBS-LRR genes. Kinship and clustering analyses based on genetic distances with susceptible cultivars representative of Central Asian Vitis vinifera indicated that 'Kishmish vatkana' and 'Dzhandzhal kara' fit well into local germplasm. 'Kishmish vatkana' also has a parent-offspring relationship with the seedless table grape 'Sultanina'. In addition, the distant genetic relatedness to rootstocks, some of which are derived from North American species resistant to powdery mildew and have been used worldwide to guard against phylloxera since the late 1800's, argues against REN1 being infused into Vitis vinifera from a recent interspecific hybridisation. CONCLUSION: The REN1 gene resides in an NBS-LRR gene cluster tightly delimited by two flanking SSR markers, which can assist in the selection of this DNA block in breeding between Vitis vinifera cultivars. The REN1 locus has multiple layers of structural complexity compared with its two closely related paralogous NBS clusters, which are located some 5 Mbp upstream and 4 Mbp downstream of the REN1 interval on the same chromosome.

Resistance to Erysiphe necator in the grapevine 'Kishmish vatkana' is controlled by a single locus through restriction of hyphal growth.

Vitis vinifera 'Kishmish vatkana', a cultivated grapevine from Central Asia, does not produce visible symptoms in response to natural or artificial inoculation with the fungus Erysiphe necator Schwein., the casual agent of powdery mildew. 'Kishmish vatkana' allowed pathogen entry into epidermal cells at a rate comparable to that in the susceptible control Vitis vinifera 'Nimrang', but was able to limit subsequent hyphal proliferation. Density of conidiophores was significantly lower in 'Kishmish vatkana' (33.6+/-8.7 conidiophores mm(-2)) than in 'Nimrang' (310.5+/-24.0 conidiophores mm(-2)) by 120 h after inoculation. A progeny of 310 plants from a 'Nimrang 'Kishmish vatkana' cross were scored for the presence or absence of visible conidiophores throughout two successive seasons. Phenotypic segregation revealed the presence of a single dominant allele termed Resistance to Erysiphe necator 1 (REN1), which was heterozygous in 'Kishmish vatkana'. A bulked segregant analysis was carried out using 195 microsatellite markers uniformly distributed across the entire genome. For each marker, association with the resistance trait was inferred by measuring in the bulks the ratio of peak intensities of the two alleles inherited from 'Kishmish vatkana'. The phenotypic locus was assigned to linkage group 13, a genomic region in which no disease resistance had been reported previously. The REN1 position was restricted to a 7.4 cM interval by analyzing the 310 offspring for the segregation of markers that surrounded the target region. The closest markers, VMC9H4-2, VMCNG4E10-1 and UDV-020, were located 0.9 cM away from the REN1 locus.