Gerald S. Dangl

Genetic structure and differentiation in cultivated grape, Vitis vinifera L.

222 cultivated (Vitis vinifera) and 22 wild (V. vinifera ssp. sylvestris) grape accessions were analysed for genetic diversity and differentiation at eight microsatellite loci. A total of 94 alleles were detected, with extensive polymorphism among the accessions. Multivariate relationships among accessions revealed 16 genetic groups structured into three clusters, supporting the classical eco-geographic grouping of grape cultivars: occidentalis, pontica and orientalis. French cultivars appeared to be distinct and showed close affinity to the wild progenitor, ssp. sylvestris from south-western France (Pyrenees) and Tunisia, probably reflecting the origin and domestication history of many of the old wine cultivars from France. There was appreciable level of differentiation between table and wine grape cultivars, and the Muscat types were somewhat distinct within the wine grapes. Contingency chi2 analysis indicated significant heterogeneity in allele frequencies among groups at all loci. The observed heterozygosities for different groups ranged from 0.625 to 0.9 with an overall average of 0.771. Genetic relationships among groups suggested hierarchical differentiation within cultivated grape. The gene diversity analysis indicated narrow divergence among groups and that most variation was found within groups (approximately 85%). Partitioning of diversity suggested that the remaining variation is somewhat structured hierarchically at different levels of differentiation. The overall organization of genetic diversity suggests that the germplasm of cultivated grape represents a single complex gene pool and that its structure is determined by strong artificial selection and a vegetative mode of reproduction.

Identification of mildew resistance in wild and cultivated Central Asian grape germplasm

BackgroundCultivated grapevines, Vitis vinifera subsp. sativa, evolved from their wild relative, V. vinifera subsp. sylvestris. They were domesticated in Central Asia in the absence of the powdery mildew fungus, Erysiphe necator, which is thought to have originated in North America. However, powdery mildew resistance has previously been discovered in two Central Asian cultivars and in Chinese Vitis species.ResultsA set of 380 unique genotypes were evaluated with data generated from 34 simple sequence repeat (SSR) markers. The set included 306 V. vinifera cultivars, 40 accessions of V. vinifera subsp. sylvestris, and 34 accessions of Vitis species from northern Pakistan, Afghanistan and China. Based on the presence of four SSR alleles previously identified as linked to the powdery mildew resistance locus, Ren1, 10 new mildew resistant genotypes were identified in the test set: eight were V. vinifera cultivars and two were V. vinifera subsp. sylvestris based on flower and seed morphology. Sequence comparison of a 620 bp region that includes the Ren1-linked allele (143 bp) of the co-segregating SSR marker SC8-0071-014, revealed that the ten newly identified genotypes have sequences that are essentially identical to the previously identified mildew resistant V. vinifera cultivars: ‘Kishmish vatkana’ and ‘Karadzhandal’. Kinship analysis determined that three of the newly identified powdery mildew resistant accessions had a relationship with ‘Kishmish vatkana’ and ‘Karadzhandal’, and that six were not related to any other accession in this study set. Clustering procedures assigned accessions into three groups: 1) Chinese species; 2) a mixed group of cultivated and wild V. vinifera; and 3) table grape cultivars, including nine of the powdery mildew resistant accessions. Gene flow was detected among the groups.ConclusionsThis study provides evidence that powdery mildew resistance is present in V. vinifera subsp. sylvestris, the dioecious wild progenitor of the cultivated grape. Four first-degree parent progeny relationships were discovered among the hermaphroditic powdery mildew resistant cultivars, supporting the existence of intentional grape breeding efforts. Although several Chinese grape species are resistant to powdery mildew, no direct genetic link to the resistance found in V. vinifera could be established.

Genetic Characterization of Grapevine Cultivars Collected throughout the Dalmatian Region

Eleven SSR loci were used to identify 76 accessions of presumed native Dalmatian grapevine cultivars (Vitis vinifera L.). Plant material was collected throughout the Dalmatian region and used to reestablish a grape germplasm collection in Dalmatia, the Adriatic region of Croatia. The 76 accessions had 63 unique genotypes, of which 35 are published here for the first time. Twelve synonyms were found within the Dalmatian cultivars and 11 Dalmatian cultivars matched previously published genotypes, mainly from neighboring countries, suggesting historic exchange of grapevine cultivars. Several cultivars with similar names had different SSR profiles, making them homonyms. Genetic distance analysis revealed five groups of cultivars and confirmed several distinct grape gene pools in Croatia.

Discovery of non-climacteric and suppressed climacteric bud sport mutations originating from a climacteric Japanese plum cultivar (Prunus salicina Lindl.)

Japanese plums are classified as climacteric; however, some economically important cultivars selected in California produce very little ethylene and require long ripening both “on” and “off” the tree to reach eating-ripe firmness. To unravel the ripening behavior of different Japanese plum cultivars, ripening was examined in the absence (air) or in the presence of ethylene or propylene (an ethylene analog) following a treatment or not with 1-methylcyclopropene (1-MCP, an ethylene action inhibitor). Detailed physiological studies revealed for the first time three distinct ripening types in plum fruit: climacteric, suppressed-climacteric, and non-climacteric. Responding to exogenous ethylene or propylene, the slow-softening supressed-climacteric cultivars produced detectable amounts of ethylene, in contrast to the novel non-climacteric cultivar that produced no ethylene and softened extremely slowly. Genetic analysis using microsatellite markers produced identical DNA profiles for the climacteric cultivars “Santa Rosa” and “July Santa Rosa,” the suppressed-climacteric cultivars “Late Santa Rosa,” “Casselman,” and “Roysum” and the novel non-climacteric “Sweet Miriam,” as expected since historic records present most of these cultivars as bud-sport mutations derived initially from “Santa Rosa.” This present study provides a novel fruit system to address the molecular basis of ripening and to develop markers that assist breeders in providing high-quality stone fruit cultivars that can remain “on-tree,” increasing fruit flavor, saving harvesting costs, and potentially reducing the need for low-temperature storage during postharvest handling.

Hybridization of cultivated Vitis vinifera with wild V. californica and V. girdiana in California.

Abstract Hybridization of introduced domesticates and closely related natives is well documented in annual crops. The widespread introduction of the domesticated grapevine, Vitis vinifera, into California where it overlaps with two native congenerics, with which it is interfertile, provides opportunity to investigate hybridization between woody perennials. Although geographically widespread, the introduction over the past two centuries has been limited to a few elite clonal cultivars, providing a unique opportunity to study the effects of hybridization on the native species. The amount of hybridization with V. vinifera and the genetic diversity of wild‐growing Vitis californica and Vitis girdiana were examined using nineteen microsatellite markers. STRUCTURE analysis was used to define hybrid and introgressed individuals and to analyze genetic structure of the native species. FAMOZ software was used to identify which V. vinifera cultivars served as parents of F 1 hybrids. The three species were clearly distinguished by STRUCTURE analysis. Thirty percent of 119 V. californica vines were hybrids. The domesticated parent was identified for 16 F 1 hybrid vines; the original California cultivar, ‘Mission’, was the parent of eight. Backcrosses were also found, showing introgression into subsequent generations. Similar results were obtained for a small sample of V. girdiana. Removing hybrids greatly reduced the genetic variation of the presumed pure species, among which there was essentially no genetic structure. Limited genetic variability indicates the California natives may be threatened by genetic erosion. The discovery of F 1 hybrids of ‘Mission’, a cultivar not grown in the areas for ~100 years, suggests long generation times for wild vines that, often, grow into expansive liana and propagate by layering, all factors that limit recruitment in populations already disjunct by habitat lose. Hermaphroditic flowers and fruit that is more attractive to birds may favor the production of backcross seed and establishment of introgressed individuals.

Additional sources of ren1-like powdery mildew resistance

The discovery of the powdery mildew resistance locus, Ren1, in two Central Asian Vitis vinifera cultivars, ?Kishmish vatkana? and ?Dzhandzhal kara?, was an important contribution to powdery mildew resistance breeding. Allelic information on the SSR markers flanking this locus enabled the screening of additional germplasm in search of other homologs carrying powdery mildew resistance genes. This study screened 392 accessions of table and wine grape varieties that originated from the Middle East, Afghanistan, Turkmenistan, Pakistan and Central Asia, as well as Chinese Vitis species, and hybrid direct producers of Native American Vitis species origin. In the first round of tests, six international standard SSR markers were used on the complete set of accessions to identify synonyms and homonyms. In the second round, ten additional markers sourced primarily from chromosome 12, 13 and 18 were utilized on a set of 266 unique accessions. The allelic diversity of marker VMCNg4e10.1 and UDV124 that flank the Ren1 locus was investigated. Thirty-one accessions were identified that had the 216 bp allele for marker UDV124 and 30 accessions had the 260 bp allele of marker VMCNg4e10.1, both of which have been associated with Ren1. The 6 accessions with resistant alleles for both markers included ?Kishmish vatkana?, ?Karadzhandal? (DVIT2323), a synonym for ?Dzhandzhal kara?, ?Husseine? (DVIT0576), ?Late Vavilov? (UCD Viticulture and Enology), ?Sochal? (DVIT1126), and ?Baidh-ul-Haman? (DVIT0358). All of the accessions with one or both alleles linked to resistance were screened under field conditions conducive to powdery mildew infection. Preliminary results indicate that four additional homologs of Ren1 have significant resistance to powdery mildew.