John E. Preece

Somatic embryogenesis in white ash ( Fraxinus americana L.)

White ash (Fraxinus americana L.), a member of the Oleaceae, is an important hardwood tree species and the most common native ash found in North America. The fast growing dioecious trees can attain heights of more than 30 meters and trunk diameters of up to 1.3 meters. Younger trees have a pyramidal or ovoid shape and mature trees have rounded tops. In landscaping, white ash is well suited for large yards and open areas such as parks and along roadsides. The wood is excellent for tool handles and sporting equipment because it is hard, strong, stiff, shock resistant, and lightweight.

Detection and genetic diversity of Grapevine red blotch-associated virus isolates in table grape accessions in the National Clonal Germplasm Repository in California

Abstract Grapevine red blotch-associated virus (GRBaV) is a recently discovered ssDNA virus that is widespread in wine grapes in California. We investigated whether GRBaV infection was present in 156 table grape accessions of Vitis vinifera that included 53 accessions exhibiting leafroll-like symptoms and 81 accessions from diverse geographic origins. Cane samples were collected during the dormant season in 2012 and analysed for GRBaV infection by PCR. A total of 73 accessions showed presence of GRBaV and these included raisin and table grape accessions with black, green and red berries. A 557 bp amplicon obtained by PCR was purified and sequenced, and the phylogenetic relationship among GRBaV isolates was examined by the maximum likelihood method. The maximum genetic variability among the isolates was only 8% and they belonged to two clades. Although it is not yet known if GRBaV is present outside of North America, 54 accessions from sources originating outside of North America tested positive for the virus.

Somatic embryogenesis in walnut (Juglans regia)

There are about 20 Juglans (walnut) species distributed through Asia, Europe, North America, and South America (Liberty Hyde Bailey Hortorium 1976). Of these species, J. regia (English or Persian walnut, primarily grown for nut production) and J. nigra (Eastern black walnut, valued mainly for its wood) are the most important commercially (McGranahan and Catlin, 1987; McGranahan and Leslie, 1990). Within the United States, the annual farm gate value of English walnuts is about

Genetic Characterization of Grapevine Cultivars Collected throughout the Dalmatian Region

150,000,000 (McGranahan, 1987). In 1987, the export value of Eastern black walnut logs from the United States was

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

13,174,000; this represented only 4.6% of the volume, but 14.9% of the total value of log exports across all species (McCurdy, 1989).

Evaluation of the phytosanitary status of the Prunus species in the National Clonal Germplasm Repository in California: survey of viruses and viroids.

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.

Genetic and ecological insights into glacial refugia of walnut (Juglans regia L.)

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.

Genetic diversity analysis of cultivated and wild grapevine ( Vitis vinifera L.) accessions around the Mediterranean basin and Central Asia

The USDA National Clonal Germplasm Repository (NGCR) at the University of California, Davis is recognized as one of the richest sources of Prunus species material in the US. The repository maintains more than 2450 trees representing 96 taxa collected from around the world. However, the phytosanitary status of the NCGR Prunus collection has not been thoroughly evaluated. In this study, a comprehensive screening of a selected subset of the collection for virus and virus-like diseases affecting Prunus trees has been completed. Two factors were considered for selecting the trees: the country of origin and the observation of suspicious disease symptoms. A total of 221 trees representing 185 different cultivars of cherry, almond, peach, apricot and plum were sampled. Conventional RT-PCR detection was used to test for 13 different viruses and two viroids. The pathogens included in the survey were Prunus necrotic ringspot virus (PNRSV), Prune dwarf virus (PDV), Plum bark necrosis stem pitting-associated virus (PBNSPaV), American plum line pattern virus (APLPV), Cherry virus A (CVA), Cherry leafroll virus (CLRV), Cherry rasp leaf virus (CRLV), Cherry green ring mottle virus (CGRMV), Cherry necrotic rusty mottle virus (CNRMV), Apple chlorotic leafspot virus (ACLSV) Tomato ringspot virus (ToRSV), Little cherry virus 1 (LChV-1), Little cherry virus 2 (LChV-2), Peach latent mosaic viroid (PLMVd) and Hop stunt viroid (HSVd). Though the majority of these trees were asymptomatic, all tested pathogens were detected except for ToRSV and CRLV. Two of the viruses detected (ACLSV and LChV-2) had never been reported from California. Incidence of PNRSV in tested trees was the highest (55 trees) followed by the two viroids (PLMVd and HSVd), with 33 and 32 infected trees, respectively. The incidence for the rest of the pathogens ranged between 0 to 19 trees. The infection rate of all tested samples ranged from 0.5% to 24.9%.

Micro- and Cutting Propagation of Silver Maple. I. Results with Adult and Juvenile Propagules

The distribution and survival of trees during the last glacial maximum (LGM) has been of interest to paleoecologists, biogeographers, and geneticists. Ecological niche models that associate species occurrence and abundance with climatic variables are widely used to gain ecological and evolutionary insights and to predict species distributions over space and time. The present study deals with the glacial history of walnut to address questions related to past distributions through genetic analysis and ecological modeling of the present, LGM and Last Interglacial (LIG) periods. A maximum entropy method was used to project the current walnut distribution model on to the LGM (21–18 kyr BP) and LIG (130–116 kyr BP) climatic conditions. Model tuning identified the walnut data set filtered at 10 km spatial resolution as the best for modeling the current distribution and to hindcast past (LGM and LIG) distributions of walnut. The current distribution model predicted southern Caucasus, parts of West and Central Asia extending into South Asia encompassing northern Afghanistan, Pakistan, northwestern Himalayan region, and southwestern Tibet, as the favorable climatic niche matching the modern distribution of walnut. The hindcast of distributions suggested the occurrence of walnut during LGM was somewhat limited to southern latitudes from southern Caucasus, Central and South Asian regions extending into southwestern Tibet, northeastern India, Himalayan region of Sikkim and Bhutan, and southeastern China. Both CCSM and MIROC projections overlapped, except that MIROC projected a significant presence of walnut in the Balkan Peninsula during the LGM. In contrast, genetic analysis of the current walnut distribution suggested a much narrower area in northern Pakistan and the surrounding areas of Afghanistan, northwestern India, and southern Tajikistan as a plausible hotspot of diversity where walnut may have survived glaciations. Overall, the findings suggest that walnut perhaps survived the last glaciations in several refugia across a wide geographic area between 30° and 45° North latitude. However, humans probably played a significant role in the recent history and modern distribution of walnut.

A Century of Progress with Vegetative Plant Propagation

BackgroundThe mountainous region between the Caucasus and China is considered to be the center of domestication for grapevine. Despite the importance of Central Asia in the history of grape growing, information about the extent and distribution of grape genetic variation in this region is limited in comparison to wild and cultivated grapevines from around the Mediterranean basin. The principal goal of this work was to survey the genetic diversity and relationships among wild and cultivated grape germplasm from the Caucasus, Central Asia, and the Mediterranean basin collectively to understand gene flow, possible domestication events and adaptive introgression.ResultsA total of 1378 wild and cultivated grapevines collected around the Mediterranean basin and from Central Asia were tested with a set of 20 nuclear SSR markers. Genetic data were analyzed (Cluster analysis, Principal Coordinate Analysis and STRUCTURE) to identify groups, and the results were validated by Nei’s genetic distance, pairwise FST analysis and assignment tests. All of these analyses identified three genetic groups: G1, wild accessions from Croatia, France, Italy and Spain; G2, wild accessions from Armenia, Azerbaijan and Georgia; and G3, cultivars from Spain, France, Italy, Georgia, Iran, Pakistan and Turkmenistan, which included a small group of wild accessions from Georgia and Croatia. Wild accessions from Georgia clustered with cultivated grape from the same area (proles pontica), but also with Western Europe (proles occidentalis), supporting Georgia as the ancient center of grapevine domestication. In addition, cluster analysis indicated that Western European wild grapes grouped with cultivated grapes from the same area, suggesting that the cultivated proles occidentalis contributed more to the early development of wine grapes than the wild vines from Eastern Europe.ConclusionsThe analysis of genetic relationships among the tested genotypes provided evidence of genetic relationships between wild and cultivated accessions in the Mediterranean basin and Central Asia. The genetic structure indicated a considerable amount of gene flow, which limited the differentiation between the two subspecies. The results also indicated that grapes with mixed ancestry occur in the regions where wild grapevines were domesticated.