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Current commercial olive (Olea europaea) cultivars are susceptible to olive knot disease caused by Pseudomonas savastanoi pv. savastanoi. Here we report on the examination of the olive tree germplasm collection maintained at the USDA-ARS National Clonal Germplasm Repository (NCGR) in Winters, California for the incidence of olive knot disease. Over a two year period we evaluated olive knot disease incidence on 506 trees representing 144 unique accessions consisting of 104 named cultivars originating from the Mediterranean Basin, South America, and California, including several hybrids, and related subspecies e.g. Olea europaea ssp. cuspidata. All genotypes were replicated in four blocks with trees in these blocks ranging in age from 6 to 35 year old. The disease index was higher in 2014 (43.5%) than in 2013 (29.4%). The percentage of infection varied significantly (P

Key message The growth of UCB-1 pistachio rootstock seedlings in the earliest years is a poor predictor of subsequent growth. Therefore, rogueing during the 1st years of growth is not effective. Abstract The UCB-1 hybrid, produced from a controlled cross between Pistacia atlantica (female) and P. integerrima (male), is the main pistachio rootstock used in the USA. Variation has been observed in orchards planted with seedling UCB-1 rootstocks for over 20 years. Reduced vigor and stunting of some trees are of particular concern to growers due to decreased nut yield. This study was conducted to better understand the growth of non-grafted UCB-1, as well as between UCB-1 rootstock and Pistacia vera scions in commercial orchards. Phenotypic traits were evaluated in the non-grafted orchard. Grafted tree data were collected for both P. vera female scions and their UCB-1 seedling rootstocks in commercial orchards. The uniformity of tree height, trunk caliper, and canopy volume decreased annually during the first 5 years of growth. Individual tree growth was not linear and was poorly synchronized among siblings, causing the population to become increasingly less uniform as it aged. Consequently, growth in the earliest years is a poor predictor of subsequent growth. The strongest correlation was between growth parameters during the later years. There was a significant correlation between rootstock and scion caliper of the grafted trees in commercial orchards, with the least vigorous rootstocks producing the least vigorous scions. These data confirm the need to reliably rogue out seedlings that later will not be vigorous; however, our data show that rogueing based on the 1st years of growth is ineffective. This study suggests the need to develop predictive molecular markers for rootstock vigor.

Background Pomegranate (Punica granatum L.) - a delicious fruit once used in Ayurvedic medicine - is now largely known for the antioxidant properties of its juice, which has also been considered to have health benefits against diseases such as cancer and cardiovascular diseases. These beneficial effects are associated with the fruit's high content of polyphenolic compounds. High demand and lower production levels drive pomegranate prices up, which leads to the possibility of pomegranate products being adulterated, diluted or substituted. To ensure the presence of pomegranate in various preparations labeled as containing pomegranate, a simple method was developed to screen and quantify the specific punicalagins by mass spectrometry. Results The present method was used to analyze several pure and mixed beverages from the US market, and also to quantify punicalagins in the juice of 14 pomegranate cultivars. Punicalagins were detected in all cultivars, with higher concentrations in whole fruit juices compared with aril juices. Amongst the 20 commercial beverages, punicalagins were not detected in four preparations. Conclusion The liquid chromatographic-mass spectrometric method presented herein enables an easy and rapid quantification of the specific punicalagins. The latter was detected in all cultivar samples, thus supporting that punicalagin is a suitable marker of these 14 pomegranate cultivars in commercial juices. Absence of the specific marker in four commercial preparations shows the necessity of having simple and rapid methods to evaluate the presence of pomegranate in preparations. © 2019 Society of Chemical Industry.

Pollination-variant persimmon (Diospyros kaki) fruit exhibits two distinct phenotypes based upon pollination status. Pollinated fruit are seeded and develop flesh that is brown in color, nonastringent, delectable in taste and highly desirable, whereas non-pollinated fruit retain unseeded orange-color flesh that is astringent and virtually unpalatable. Growers face the problem that both types of flesh may be present in the same persimmon fruit, and external skin color is uniformly orange, regardless of the extent of astringency. Thus, in this work, the nondestructive measurement modalities of nuclear magnetic resonance (NMR) relaxometry and near-infrared (NIR) spectroscopy were investigated for their ability to screen pollination-variant persimmons for extent of nonastringent flesh. Fruit from a diverse sample set – including six cultivars stored for varying lengths of time and exhibiting an array of astringency levels – was subjected to the two nondestructive measurements and then evaluated destructively for astringency using a sequential blotting and visual sensory analysis approach. The sensory astringency score was then used as the response variable to construct partial least squares – discriminant analysis (PLS-DA) models from spectra from each modality on its own as well as for concatenated spectra, which combined the information from both modalities. These PLS-DA models performed well, showing a maximum misclassification rate of 33%. When the most market-relevant astringency threshold was used, NIR slightly outperformed NMR. When different astringency screening thresholds were considered, combining the two modalities did not consistently improve PLS-DA model performance. Thus, both modalities show promise for nondestructive characterization of the flesh of pollination-variant persimmons.

Persimmon (Diospyros kaki) is an underutilized tree fruit. Previous studies have shown the feasibility of making a hot-air-dried, chip-style product from persimmon. However, the texture of this type of product has not been explored or connected to consumer preference. Thus, for dried samples representing 37 cultivars, this study aimed to (1) predict trained sensory panel texture attributes from instrumental measurements, (2) predict consumer liking from instrumental measurements and sensory texture attributes, and (3) elucidate whether astringency type affects dried product texture. Partial least-squares regression models of fair-to-good quality predicted all measured sensory texture attributes (except Tooth Packing) from instrumental measurements. Modeling also identified that consumer preference is for a moist, smooth texture. Lastly, while astringency type has significant (p &lt, 0.05) effects on several individual texture attributes, astringency type should not be used a priori to screen-in or -out persimmon cultivars for processing into a hot-air-dried product.

Pomegranate is an ancient tree fruit that has been domesticated for thousands of years and cultivated for its fruit, juice, and arils. Despite its long history of cultivation, limited consistent and reliable information on fertilizer requirements is available to growers. More scientifically based information is needed on pomegranate nutrition so that yield and profitability can be optimized for farm sustainability. It is also important that fertilizers are used responsibly so that ecological harm often associated with agricultural systems is minimized. This chapter contains grower pertinent information on pomegranate tree nutrition and management for specific growing conditions. Pomegranate is not difficult to cultivate when grown in the appropriate climate with the appropriate resources. Leaf tissue nutrition sufficiency range values are reported herein with associated yields so that growers can determine if fertilization is needed. Investigations involving nutrition of “Wonderful” pomegranate are reported from the authors’ research program and published works.

Grapevine virus T (GVT) is a new member of the genus Foveavirus and has been reported to infect grapevines in several European countries. In 2018, GVT was detected for the first time in California in a domestic selection of wine grape, cv. Lambrusca di Alessandria, via high-throughput sequencing (HTS). To further investigate the presence of GVT in other grapevine plants, a two-step reverse transcription (RT)-PCR assay involving degenerate primers was developed. In order to cover the high genetic diversity of GVT, the sequences of available isolates were aligned to identify a conserved region in the coat protein gene that was a suitable target for the assay. The results of the RT-PCR assay showed that GVT was present in three additional grapevine selections among 416 plants integrating the Foundation Plant Services introduction pipeline; all were later confirmed by HTS. A complete and three near-complete genomes of the four GVT isolates were characterized and found to be divergent, sharing an overall 81 % pairwise identity in their nucleotide sequences. This suggested that the new RT-PCR assay was effective in detecting a broad range of GVT variants. The RT-PCR detection method developed in this study would be useful for routine virus testing.

Pomegranate (Punica granatum L.) is a deciduous tree crop. Its fruit are known to have relatively high concentrations of polyphenolic compounds and antioxidant properties. The USDA-ARS pomegranate germplasm collection maintains over 250 cultivars, but most have not been evaluated for optimal harvest dates or fruit quality. In the following investigation, pomegranate germplasm was evaluated to determine optimal harvest windows, identify cultivars with consumer-friendly traits, and to compare fruit quality with the industry standard, ‘Wonderful.’ Fruit from ten cultivars were analyzed for the following traits: fruit weight, fruit diameter, fruit length, calyx diameter, calyx length, weight of 100 arils, weight of all arils, edible portion of fruit, oBrix, titratable acidity (TA) (% in citric acid equivalents), maturity index (MI) (sugar to acid ratio), antioxidant activity (AA) (% inhibition of DPPH), and total phenolics (mg/L in gallic acid equivalents). Cultivars selected from the germplasm included those similar to ‘Wonderful’ as well as cultivars with other traits, such as softer seeds, which could meet wider consumer demand. Many trait values increased over time (oBrix, MI, etc.), while some decreased over time (AA, TA). Sugar to acid ratio was used as the MI and there were significant differences among cultivars. Lower acid, sweet cultivars had higher MI than sweet-tart, tart, and sour cultivars. For cultivars with high sugar to acid ratios, growers may need a different MI from ‘Wonderful’ to determine fruit maturity for commercial production.

Pomegranate (Punica granatumL.) is an important fruit in many cultures. The fruit and juice have risen in popularity as it was discovered that pomegranate has relatively high antioxidant activity compared to most other fruits. In this study, six cultivars were utilized to determine consumer acceptance compared to the industry standard, ‘Wonderful,’ which comprises 90% to 95% of commercial production in the United States. Fruit were sourced from 2 cultivar field trials, one in inland Riverside, California, and one in coastal Ventura County, California. Cultivars selected for the study included ‘Eversweet,’ ‘Green Globe,’ ‘Haku Botan,’ ‘Loffani,’ ‘Phoenicia,’ ‘Wonderful,’ and ‘cv. 857,’ an heirloom cultivar from Ventura County, CA, U.S.A. Pomegranate arils were subject to sensory evaluation by 87 untrained consumer panelists in late 2016. Panelists were given pomegranate arils and asked to score the samples using a 9‐point Hedonic scale for the following fruit quality traits: aril color, sweetness, tartness, seed hardness, bitterness, and overall desirability. There were significant differences among cultivars for all traits assessed by the sensory panelists. There were differences in acceptance among consumers for ‘Wonderful’ depending on if it was grown on the coast versus inland, and consumers preferred inland‐ versus coastal‐grown ‘Wonderful.’ ‘Wonderful’ pomegranate was associated with cultivars that consumers scored low on desirability for bitterness. Cultivars that scored well in overall desirability compared with ‘Wonderful’ were ‘cv. 857,’ ‘Eversweet,’ ‘Green Globe,’ and ‘Phoenicia.’ Consumer sensory panels are important to determine scientifically which cultivars are desired by the public. These panels allowed for the determination of which pomegranate cultivars are liked or disliked by consumers and why. If the pomegranate growers know the most desirable cultivars for consumers, they are more likely to adopt and plant them, thus potentially increasing the diversity in the marketplace, as has been with apples, peaches, plums, pears, mangoes, strawberries, raspberries, blueberries, and citrus.

Commercial pomegranate production area has increased substantially in the western hemisphere due to increased consumer interest in the fruit. Low nursery inventory has caused many growers to propagate vegetatively their own trees and the availability of only a few cultivars is believed to have played a role in a lack of diversity in the developing market. ‘Wonderful,’ the industry standard for pomegranate in several countries, has been propagated in the United States for over 100 years, yet there is limited scientific information regarding how to most effectively propagate ‘Wonderful’ and other important cultivars. This research included two experiments. Experiment 1 evaluated rooting percentages and vegetative growth attributes of hardwood cuttings of twelve cultivars (‘Ambrosia,’ ‘Desertnyi,’ ‘Eversweet,’ ‘Golden Globe,’ ‘Green Globe,’ ‘Haku Botan,’ ‘Ki Zakuro,’ ‘Loffani,’ ‘Nochi Shibori,’ ‘Parfianka,’ ‘Phoenicia,’ and ‘Wonderful’) utilizing a basal dip in a gel formulation of 3 g·L−1 indole-3-butyric acid (IBA). Experiment 2 evaluated auxin treatments which consisted of basal dip in water only (control) or a gel formulation of IBA (1.5 g L−1 or 3 g L−1) for hardwood cuttings of ‘Wonderful’ and two cultivars that rooted poorly in Experiment 1 : ‘Ambrosia’ and ‘Green Globe.’ Measured response attributes included rooting success percentages, dry root mass, leaf area, plant height, number of shoots, apical shoot growth, total shoot length, branching, stem diameter, and relative chlorophyll content (SPAD value). ‘Wonderful’ and nine other cultivars rooted over 84% of the time using cuttings treated with 3 g L−1 IBA. Differences in plant height and branching could be detected early in production. The effect of IBA concentration on rooting percentage and growth attributes varied among cultivars. Cuttings of ‘Ambrosia’ rooted best with 3 g L−1 IBA versus 0 and 1.5 g L−1 IBA, whereas rooting of cuttings of ‘Green Globe’ was similar among IBA rates. Plants of ‘Wonderful’ had significantly greater leaf area compared to those of ‘Ambrosia’ and ‘Green Globe.’ Stem diameter had no effect on rooting on any cultivar in either experiment. There were significant differences among cultivars in terms of chlorophyll content, with ‘Haku Botan’ and ‘Loffani’ having greener leaves than ‘Eversweet,’ ‘Ambrosia,’ and ‘Desertnyi.’

Green shoot cuttings of 10 different grapevine species were inoculated with Agrobacterium vitis to find disease-related metabolites in the grapevine. Crown galls formed 60 days after inoculation varied in gall severity (GS) evaluated by gall incidence (GI) and gall diameter (GD), which were classified into three response types as RR (low GI and small GD), SR (high GI and small GD), and SS (high GI and large GD), corresponding to resistant, moderately resistant, and susceptible responses, respectively. In this, 4, 4, and 2 Vitis species were classified into RR, SR, and SS, respectively. Gas chromatography mass spectrometry (GC-MS) analysis of the grapevine stem metabolites with A. vitis infection showed 134 metabolites in various compound classes critically occurred, which were differentially clustered with the response types by the principal component analysis. Multivariate analysis of the metabolite profile revealed that 11 metabolites increased significantly in relation to the response types, mostly at post-inoculation stages, more prevalently (8 metabolites) at two days after inoculation than other stages, and more related to SS (7 metabolites) than RR (3 metabolites) or SR (one metabolite). This suggests most of the disease-related metabolites may be rarely pre-existing but mostly induced by pathogen infection largely for facilitating gall development except stilbene compound resveratrol, a phytoalexin that may be involved in the resistance response. All of these aspects may be used for the selection of resistant grapevine cultivars and their rootstocks for the control of the crown gall disease of the grapevine.

The asexual propagation of clonal crops has allowed cultivation of superior selections for thousands of years. With time, some clones deteriorate from genetic and epigenetic changes. Non-infectious bud-failure (NBF) in cultivated almond (Prunus dulcis) is a commercially important age-related disorder that results in the failure of new vegetative buds to grow in the spring, with dieback of terminal shoots, witches-brooming of surviving buds, and deformed bark (roughbark). The incidence of NBF increases with clone age, including within individual long-lived trees as well as nursery propagation lineages. It is not associated with any infectious disease agents. Consequently, nursery practices emphasize the establishment of foundation-mother blocks utilizing propagation-wood selected from proven and well-monitored propagation-lineages. Commercial propagation utilizes axillary shoot buds through traditional budding or grafting. This study examines NBF development using basal epicormic buds from individual trees of advanced age as an alternative source of foundation stock. Results show the age-related progression of NBF is suppressed in these epicormic meristems, possibly owing to their unique origins and ontogeny. NBF development in commercial orchards propagated from foundation blocks established from these sources was similarly dramatically suppressed even over the 10- to 20-year expected commercial orchard-life. Foundation-stock stability can be further maintained through appropriate management of propagation source-trees, which requires accurate knowledge of meristem origin and development.

Pistachio (Pistacia vera L.) trees from the National Clonal Germplasm Repository (NCGR) and orchards in California were surveyed for viruses and virus-like agents by high-throughput sequencing (HTS). Analyses of sequence information from 60 trees identified a novel virus, provisionally named “Pistachio ampelovirus A” (PAVA), in the NCGR that showed low amino acid sequence identity (approximately 42%) compared with members of the genus Ampelovirus (family Closteroviridae). A putative viroid, provisionally named “Citrus bark cracking viroid-pistachio” (CBCVd-pis), was also found in the NCGR and showed approximately 87% similarity to Citrus bark cracking viroid (CBCVd, genus Cocadviroid, family Pospiviroidae). Both PAVA and CBCVd-pis were graft transmissible to healthy UCB-1 hybrid rootstock seedlings (P. atlantica × P. integerrima). A field survey of 123 trees from commercial orchards found no incidence of PAVA but five (4%) samples were infected with CBCVd-pis. Of 675 NCGR trees, 16 (2.3%) were positive for PAVA and 172 (25.4%) were positive for CBCVd-pis by reverse-transcription polymerase chain reaction. Additionally, several contigs across multiple samples exhibited significant sequence similarity to a number of other plant virus species in different families. These findings require further study and confirmation. This study establishes the occurrence of viral and viroid populations infecting pistachio trees.

Pecan is the only major nut crop native to North America; however, many important wild relative species of nut crops, including chestnut, hazelnut, pecan, pistachio, and walnut, are native to North America and are important sources of useful genes. This chapter briefly covers the history and use of temperate nut crops and more thoroughly discusses the occurrence, potential usefulness, and conservation status of North American crop wild species that have potential value in nut crop improvement.

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.

Wild Prunus germplasm is an important resource for pest and disease resistance traits for the continued improvement of almond and other Prunus rootstocks. Evaluation of resistance in these wild species requires clonal replicates that are traditionally produced by rooting cuttings. Over two consecutive years, leafy cuttings of 20 genotypes of the following wild Prunus species were collected in mid-late May and treated with a 15 s dip in 0, 500, 1000, 2000 or 4000 mg/L of the potassium salt of indole-3-butyric acid (KIBA): almonds (P. argentea (one genotype), P. bucharica (two genotypes), P. dulcis (two genotypes), P. tangutica (three genotypes)), peaches (P. davidiana (two genotypes), P. kansuensis, P. mira (two genotypes), P. persica (three genotypes including a commercial peach rootstock, ‘Lovell’)), and plums (P. cerasifera (two genotypes), P. salicina (two genotypes)).. The cuttings were planted in a perlite-vermiculite medium under intermittent mist and periodically checked for roots. The plum species rooted at a higher percentage, and produced more roots than the peach species; and the almond species generally failed to root. The plums produced the most roots at 2000−4000 mg/L KIBA, although rooting in both P. cerasifera and P. salicina was genotype dependent. The plum cuttings that rooted generally produced from 2 to 14 roots that averaged 0.74–1.73 cm long when the cuttings were harvested; one accession produced 60 roots/cutting when treated with 4000 mg/L KIBA. The wild peach species produced the most roots at 1000−4000 mg/L KIBA, with cuttings of P. kansuensis and P. mira having significantly higher rooting percentages than P. davidiana and P. persica cuttings. All of the wild almond species tested did not root or rooted a very low percentage.

Background The 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. Results A 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. Conclusions The 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. Electronic supplementary material The online version of this article (10.1186/s12870-018-1351-0) contains supplementary material, which is available to authorized users.

California faces many threats to food security, ranging from water limitations resulting from long-term drought to invasive pests and diseases. Major tree crops, such as citrus and avocado, are threatened by Citrus Greening and Fusarium Dieback, respectively, posing significant economic losses to growers and farm sustainability. Pomegranate (Punica granatum L.) was previously a minor tree crop in California, but has become an important specialty crop, with planted area increased by 10-fold during the last twenty years, and is currently a $200 million annual industry. Pomegranate is not threatened so far by any pest or disease and is a drought- and salt-tolerant crop that can be cultivated on marginal land, which makes it an attractive alternative crop for the growers facing water and disease issues. For this investigation, two pomegranate field trials were initiated and followed over four years to evaluate site effects on establishment, precocity, photosynthesis and water relations to assist in determining appropriate cultivars for coastal versus inland climates. Traits measured included orchard establishment, photosynthesis, water potential, and flowering and yield traits. There were significant site and cultivar effects on many traits as well as site-cultivar interactions. The coastal trial grew significantly faster than the semi-arid inland site, however, the inland site was more productive than the coastal site for the first three years. Production during year four of establishment was similar at both sites.

Pomegranate (Punica granatum L.) is an important fruit in many cultures. The fruit and juice have risen in popularity as it was discovered that pomegranate has relatively high antioxidant activity compared to most other fruits. In this study, six cultivars were utilized to determine consumer acceptance compared to the industry standard, 'Wonderful,' which comprises 90% to 95% of commercial production in the United States. Fruit were sourced from 2 cultivar field trials, one in inland Riverside, California, and one in coastal Ventura County, California. Cultivars selected for the study included 'Eversweet,' 'Green Globe,' 'Haku Botan,' 'Loffani,' 'Phoenicia,' 'Wonderful,' and 'cv. 857,' an heirloom cultivar from Ventura County, CA, U.S.A. Pomegranate arils were subject to sensory evaluation by 87 untrained consumer panelists in late 2016. Panelists were given pomegranate arils and asked to score the samples using a 9-point Hedonic scale for the following fruit quality traits: aril color, sweetness, tartness, seed hardness, bitterness, and overall desirability. There were significant differences among cultivars for all traits assessed by the sensory panelists. There were differences in acceptance among consumers for 'Wonderful' depending on if it was grown on the coast versus inland, and consumers preferred inland- versus coastal-grown 'Wonderful.' 'Wonderful' pomegranate was associated with cultivars that consumers scored low on desirability for bitterness. Cultivars that scored well in overall desirability compared with 'Wonderful' were 'cv. 857,' 'Eversweet,' 'Green Globe,' and 'Phoenicia.'Consumer sensory panels are important to determine scientifically which cultivars are desired by the public. These panels allowed for the determination of which pomegranate cultivars are liked or disliked by consumers and why. If the pomegranate growers know the most desirable cultivars for consumers, they are more likely to adopt and plant them, thus potentially increasing the diversity in the marketplace, as has been with apples, peaches, plums, pears, mangoes, strawberries, raspberries, blueberries, and citrus.

The National Clonal Germplasm Repository (NCGR) in Davis is one among the nine repositories in the National Plant Germplasm System, USDA-ARS, that is responsible for conservation of clonally propagated woody perennial subtropical and temperate fruit and nut crop germplasm. Currently the repository holds over 6500 accessions of germplasm of Actinidia (kiwi fruit), Diospyros (persimmon), Ficus (fig), Juglans (walnuts), Morus (mulberry), Olea (olive), Pistacia (pistachio), Prunus (stonefruits and almond), Punica (pomegranate), Vitis (grape), and other minor genera. Wild relatives are widely represented in these collections with about 91% of the taxa and 43% of the total accessions representing the wild gene pools. Research at the repository is mainly focused on genetic characterization of germplasm using molecular markers and morphological traits to quantify and describe genetic structure and differentiation within and among species and gene pools. Promoting the use of crop wild relatives (CWR) germplasm in genetic improvement of tree fruit and nut crops is our top priority. Presently, at the Davis repository, we are extensively utilizing Prunus and Juglans wild relatives for developing improved rootstocks with resistance to biotic and abiotic stresses. We will review and discuss the results of ongoing programs highlighting the importance of different CWRs as donors of genes for resistance to major soil borne diseases such as crown gall, Phytophthora rots, and nematodes in the rootstock improvement programs. Breeding for drought tolerance is another major thrust for which we are screening CWR germplasm to identify novel sources of drought tolerance to infuse into ongoing rootstock breeding programs.

Luther Burbank began making controlled crosses between walnut species in the late 19th century after hearing about a “supposed natural European hybrid walnut.” He crossed Juglans hindsii (northern California black walnut) × J. regia (Persian walnut) and produced progeny that he named ‘Paradox’ because of its extremely fast growth and other “anomalies.” He also crossed two American species, J. hindsii × J. nigra (eastern black walnut), producing ‘Royal’ walnut progeny that were fast-growing and prolific nut producers. A third interspecific hybrid was a cross between J. ailantifolia (Japanese walnut) × J. regia that resulted in extremely vigorous progeny but was not named. He observed segregation in the F2 populations and described giants and dwarfs as reversions to ancestral forms. Luther Burbank also made selections for walnut scion cultivars and was especially interested in thin-shelled nuts. He collected seeds from a J. regia growing in San Francisco because it produced regularly and had very high-quality nuts with relatively thin but poorly sealed shells. He selected one of its seedlings as ‘Santa Rosa Soft-Shell’ and described it as bearing large crops of nuts that were nearly white with thin shells and delicious white meat. Burbank’s contributions to the walnut industry endure to this day, especially through the widespread use of seedling and clonal ‘Paradox’ walnut rootstocks.

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.

This work aimed to characterize the sensory attributes of hot air‐dried persimmon (Diospyros kaki) chips, correlate these attributes with consumer hedonic information, and, by doing so, present recommendations for cultivars that are most suitable for hot‐air drying. A trained sensory panel evaluated dried persimmon samples (representing 40 cultivars) for flavor, taste/aftertaste, and texture. In addition, in each of two tests conducted in different years, more than 100 consumers provided hedonic evaluations of 21 unique samples in a ranking task with a balanced incomplete block design. A partial least squares regression model correlating the mean hedonic ranking to the trained panel data was developed using the data from the first consumer panel. The predictions from the model were correlated with the second panel to verify the model. It was found that including taste, aftertaste, and texture data (but not specific flavor attribute data) produced a predictive model (Spearman's ρ=0.83). This indicates that flavor is likely secondary to taste and texture in dried persimmon chips. Using the validated predictive model, 6 of the 40 persimmon cultivars tested are recommended for a dried chip product; these cultivars are ‘Fuyu’, ‘Lycopersicon’, ‘Maekawa Jiro’, ‘Nishimura Wase’, ‘Tishihtzu’, and ‘Yotsumizo’.

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.

This work aimed to characterize the sensory attributes of hot air-dried persimmon (Diospyros kaki) chips, correlate these attributes with consumer hedonic information, and, by doing so, present recommendations for cultivars that are most suitable for hot-air drying. A trained sensory panel evaluated dried persimmon samples (representing 40 cultivars) for flavor, taste/aftertaste, and texture. In addition, in each of two tests conducted in different years, more than 100 consumers provided hedonic evaluations of 21 unique samples in a ranking task with a balanced incomplete block design. A partial least squares regression model correlating the mean hedonic ranking to the trained panel data was developed using the data from the first consumer panel. The predictions from the model were correlated with the second panel to verify the model. It was found that including taste, aftertaste, and texture data (but not specific flavor attribute data) produced a predictive model (Spearman's ρ=0.83). This indicates that flavor is likely secondary to taste and texture in dried persimmon chips. Using the validated predictive model, 6 of the 40 persimmon cultivars tested are recommended for a dried chip product; these cultivars are ‘Fuyu’, ‘Lycopersicon’, ‘Maekawa Jiro’, ‘Nishimura Wase’, ‘Tishihtzu’, and ‘Yotsumizo’.

The National Clonal Germplasm Repository in Davis, CA is a United States Department of Agriculture (USDA), Agricultural Research Service (ARS) genebank that houses national collections of various Mediterranean fruit and nut crops. The Prunus collection is the second largest in this genebank and is exceeded only by Vitis (grapes). There are more than 90 taxa and in excess of 1600 accessions of Prunus spp. in the collection that includes almonds, apricots, cherries, peaches, and plums. The mission of the genebank is to acquire, maintain, evaluate, and distribute germplasm. Acquisition is from plant collection trips and donations of germplasm to the repository and includes cultivars, breeding lines, and Prunus wild relatives. The trees are propagated and maintained in the Wolfskill Experimental Orchard near Winters, CA and in containers in screen houses in Davis. Evaluation data are compiled on phenotype and genotype and are freely available online at the Germplasm Resources Information Network (GRIN), see: http://www.ars-grin.gov/ cgi-bin/npgs/html/site_holding.pl?DAV. As a part of genetic characterization of germplasm at the Davis repository, an analysis of genetic diversity and differentiation using fifteen SSR loci among five diploid Prunus spp. revealed significant variability within and among species with a number of species specific alleles of low to moderate frequencies. The average number alleles/locus across the 15 loci assayed ranged from 6.93 for peach (P. persica) to 18.27 for almond (P. dulcis) with an overall average of 11.38 alleles/locus. Among the cultivated species, the observed and expected heterozygosities were relatively higher except for P. persica with 0.3247 and 0.4351 for observed and expected levels, respectively and with the lowest average number of alleles across loci (6.93) among the cultivated species. Within population genetic variability measures indicated that P. dulcis is the most highly variable species among the cultivated Prunus followed by P. ceracifera, P. armeniaca and P. salicina. As expected, peach and almond showed close genetic affinity followed by diploid plums, and apricots. The results are summarized as applied to genetic conservation, management, and utilization of Prunus germplasm.

Eleven SSR loci were used to identify 76 accessions of presumed native Dalmatian grapevine cultivars (Vitis vinifera L.). The 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 these 35 are not published in peer-reviewed journals. Twelve synonyms were found within the Dalmatian cultivars and eleven Dalmatian cultivars matched previously published genotypes, mainly from neighboring countries, suggesting historic exchange of grapevine cultivars along ancient trade routes across the Adriatic Sea. Several cultivars with similar names had different SSR profiles, making them homonyms. Genetic distance analysis revealed five groups of cultivars and confirms the existence of several distinct grape gene pools in Croatia.

Greenhouse studies were conducted on two southern Illinois star-of-Bethlehem populations to determine the influence of chilling and bulb chipping on plant growth and reproduction. Chilling was not required for leaf emergence of dormant bulbs, but an increase to 10 wk of chilling proportionally delayed leaf emergence by 41 and 42 d for the Murphysboro and the Marion populations, respectively. Bulb chipping did reduce plant height when compared to plants from nonchipped bulbs. Also, chipped bulbs produced a greater number of small daughter bulbs compared to nonchipped bulbs; however, total bulblet production was variable and dependent on population, mother bulb size, and chipping treatment. Overall, bulb chipping did not have any negative influence on star-of-Bethlehem and might promote increased daughter bulblet production. Therefore, field operations, such as tillage, that cut and chip bulbs might actually accentuate both the spread and density of star-of-Bethlehem infestations.

Phenolic and other compounds were extracted from micropropagated axillary shoots (microshoots) of the walnut (Juglans regia L.) cultivars ‘Chandler’, ‘Howard’, ‘Kerman’, ‘Sunland’, and ‘Z63’. Among cultivars, microshoots showed differences in phenolic compounds, phenolic acids, flavonoids, and proanthocyanidins. All cultivars contained the phenolics acids chlorogenic acid, gallic acid, p-coumaric acid; the naphthoquinone juglone; and the flavonoid quercetin. The phenolic acids syringic acid and vanillin were present only in microshoots of ‘Howard’. Microshoot extracts had different antioxidant activity with ‘Kerman’ the highest and ‘Chandler’ the lowest in each of three antioxidant assays: the phosphomolybdenum assay (PPM), reducing power assay, and 2,2-diphenyl-1-picrylhydrazyl-scavenging effect. There was a strong linear relationship between total phenolic compound content of microshoots and increasing antioxidant activity.

Somatic embryogenesis was obtained from immature cotyledon explants that were cultured on half-strength Murashige and Skoog (MS) salts and vitamins with 5.4 μM naphthaleneacetic acid (NAA) and 0.2 μM thidiazuron (TDZ) plus a 4 × 4 factorial combination of 0, 9.8, 24.6, or 49.2 μM indole-3-butyric acid (IBA) and 0, 8.9, 22.2, or 44.4 μM 6-benzyladenine (BA). The addition of 44.4 μM BA improved the percentage of cotyledon explants that produced somatic embryos to >20%, if 9.8 or 24.6 μM IBA was also present. Somatic embryogenesis was >30% when seeds were harvested on 31 July or 15 August. The addition of 50 or 70 g l−1 sucrose enhanced embryogenesis. Histological examination showed that somatic embryos originated from epidermis cells of zygotic embryos. A peak germination rate (69%) was attained when somatic embryos were desiccated for 10 min before they produced green cotyledons and elongating shoot tips. Of the germinated embryos from this desiccation treatment, 65.6% also grew roots and therefore converted into plants. Chilling somatic embryos at 4°C for 15 days resulted in the highest germination rate (69.4%), which was significantly higher than those without chilling treatment (27.6%). However

The conservation status of the northern California black walnut (Juglans hindsii (Jeps.) Jeps. ex R. E. Sm.) has been a source of considerable confusion and controversy. Although not currently legally protected by either Federal or State Endangered Species Acts, this species is given conservation status by the California Native Plant Society and the California Department of Fish and Wildlife, and some California counties require mitigation for removal of individuals of this species, especially older trees. Despite the current widespread distribution in northern California and southern Oregon of trees that match J. hindsii morphologically, there are only three or four sites where the species is known to have occurred prior to extensive settlement of California by Europeans in the mid-19th century. This has led to the suspicion that trees found in other places may not be genetically pure J. hindsii but may instead be descendants of lineages that experienced past gene flow from one or more other species. In addition, despite its more distant relationship, the cultivated walnut (J. regia L.) readily hybridizes (as the male parent) with J. hindsii, producing morphologically identifiable ‘Paradox' hybrids, which occur spontaneously and are widely planted as rootstocks and street trees. Finally, recent collections of J. hindsii from southern California have raised questions about the respective geographic distributions of J. hindsii and southern California black walnut (J. californica S. Watson). We analyzed genotypes at 10 microsatellite loci for 158 mostly wild J. hindsii trees, as well as some orchard waifs, from 10 counties in northern and southern California and one county in southern Oregon, including representatives of putative original native populations. We also sampled several Paradox hybrids, 10-20 standards for each of the five North American black walnut species, and six standards for J. regia. Bayesian cluster analyses with the program STRUCTURE revealed that at least 71.5% of the putatively wild J. hindsii represent genetically pure members of that species, while the remaining trees show evidence of past hybridizations with one or more of the other North American black walnut species. We found no evidence of introgression of J. regia into J. hindsii. The results suggest that individual J. hindsii trees should not have conservation status.