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‘Nemaguard’ is a commonly used rootstock for almond and stone fruits due to resistance to nematodes and enhanced scion vigor. Nemaguard also happens to be resistant to strains of Xylella fastidiosa that cause almond leaf scorch disease. Previous research showed that prior to June-budding, this rootstock can prevent infection of almond nursery stock by X. fastidiosa. Further, the rootstock also promotes recovery from infection in susceptible almond scions. Objectives of this study were to 1) compare movement and bacterial populations of X. fastidiosa in almond and Nemaguard, 2) determine whether the metabolic profile of infected versus noninfected plants of each species correspond with differences in pathogen distribution, and 3) evaluate the impact of feeding on Nemaguard on transmission efficiency and pathogen populations in insects. Results showed limited or no movement of X. fastidiosa beyond the point of mechanical inoculation in Nemaguard, whereas X. fastidiosa was detected in susceptible almond and isolated from plant samples distal to the point of inoculation. Large differences in the concentration of phenolic compounds between Nemaguard and almond were also found, although this was not impacted by infection status. After acquiring X. fastidiosa from infected plants, vector access periods of up to 14 days on Nemaguard neither reduced pathogen populations in vectors nor reduced transmission efficiency of X. fastidiosa to susceptible plants when compared with similar vector-access periods on susceptible grapevines. Results suggest Nemaguard, in spite of having high phenolic concentrations in its xylem, does not directly impact X. fastidiosa survival and that future research should focus on identification of potential physical traits that prevent bacterial attachment, multiplication, or movement within the plant.

Race-specific resistance loci, whether having qualitative or quantitative effects, present plant-breeding challenges for phenotypic selection and deciding which loci to select or stack with other resistance loci for improved durability. Previously, resistance to grapevine powdery mildew (GPM, caused by Erysiphe necator) was predicted to be conferred by at least three race-specific loci in the mapping family B37-28 × C56-11 segregating for GPM resistance from Vitis aestivalis. In this study, 9 years of vineyard GPM disease severity ratings plus a greenhouse and laboratory assays were genetically mapped, using a rhAmpSeq core genome marker platform with 2,000 local haplotype markers. A new qualitative resistance locus, named REN11, on the chromosome (Chr) 15 was found to be effective in nearly all (11 of 12) vineyard environments on leaves, rachis, berries, and most of the time (7 of 12) stems. REN11 was independently validated in a pseudo-testcross with the grandparent source of resistance, “Tamiami.” Five other loci significantly predicted GPM severity on leaves in only one or two environments, which could indicate race-specific resistance or their roles in different timepoints in epidemic progress. Loci on Chr 8 and 9 reproducibly predicted disease severity on stems but not on other tissues and had additive effects with REN11 on the stems. The rhAmpSeq local haplotype sequences published in this study for REN11 and Chr 8 and 9 stem quantitative trait locus (QTL) can be used directly for marker-assisted selection or converted to SNP assays. In screening for REN11 in a diversity panel of 20,651 vines representing the diversity of Vitis, this rhAmpSeq haplotype had a false positive rate of 0.034% or less. The effects of the other foliar resistance loci detected in this study seem too unstable for genetic improvement regardless of quantitative effect size, whether due to race specificity or other environmental variables.

The impact of mechanized raisin harvesting has been positive in terms of reducing crop losses due to the development of cultivars that exhibit the natural dry-on-vine (NDOV) trait in grape germplasm. However, while drying rates of specific genotypes are being determined and cultivars are being released, the genetic components influencing the NDOV trait are not yet known. A deeper understanding of genetic mechanisms influencing NDOV will enable scientists to develop tools for breeding applications, such as molecular markers for seedling selection, and allow the formulation of strategies for the further study of NDOV and its biochemical basis, which may provide insights for agricultural management practices. Previous genetic mapping attempts of the NDOV trait using distinct phenotypic data were unsuccessful. A study in tomato demonstrated that the gene Cpw1 affects fruit cuticle leading to fruit dehydration on the plant. Hence, Cpw1 was selected as a potential candidate underlying the NDOV phenotype in grapevine. By using the grapevine genome reference sequence, two loci were identified as having high homology to tomato Cpw1, one on chromosome 3 and another on chromosome 18, the latter having the higher homology and therefore being named VviCpw1. Sequences of these loci were retrieved from the genome sequences of ‘Thompson Seedless’, ‘Pinot Noir’, ‘Flame Seedless’, ‘Cabernet Sauvignon’ and Vitis cinerea B9 and used for multiple sequence alignments for homology quantification and identification of putative polymorphisms. The DNA sequence of VviCpw1 was cloned from the NDOV raisin cultivar ‘Sunpreme’ and introduced into tomato to verify function. In addition, screening for polymorphisms in raisin-related germplasm, with and without the NDOV trait, is underway using AmpSeq, while obtaining supporting phenotypic data from NDOV-segregating germplasm. Studies on cuticle features are also envisioned. Results from this study will enable the development of tools and a body of knowledge for the further understanding of the NDOV trait in grapevine.

The availability of powdery mildew-resistant raisin accessions will lower grower production costs and enhance the environment through reduced fungicide use. To achieve this objective, backcrossing ...

Transferable DNA markers are essential for breeding and genetics. Grapevine (Vitis) breeders utilize disease resistance alleles from congeneric species ~20 million years divergent, but existing Vitis marker platforms have cross-species transfer rates as low as 2%. Here, we apply a marker strategy targeting the inferred Vitis core genome. Incorporating seven linked-read de novo assemblies and three existing assemblies, the Vitis collinear core genome is estimated to converge at 39.8 Mb (8.67% of the genome). Adding shotgun genome sequences from 40 accessions enables identification of conserved core PCR primer binding sites flanking polymorphic haplotypes with high information content. From these target regions, we develop 2,000 rhAmpSeq markers as a PCR multiplex and validate the panel in four biparental populations spanning the diversity of the Vitis genus, showing transferability increases to 91.9%. This marker development strategy should be widely applicable for genetic studies in many taxa, particularly those ~20 million years divergent., Trait introgression requires universal markers, but cross-species transferability of current SNP markers can be as low as 2%. Here, the authors use an AmpSeq haplotype strategy targeting the collinear core genome for marker development and show transferability increases to 91.4% in the Vitis genus.

Almond leaf scorch (ALS) disease has been present in California's almond-growing regions for over 60 years. This disease is caused by the bacterium Xylella fastidiosa and the pathogen is vectored by xylem-feeding sharpshooters and spittlebugs. Currently, there are no effective management techniques that prevent trees from becoming infected. Within affected orchards throughout California's Central Valley, disease incidence and the risk of tree-to-tree spread appears to be low. Consequently, the decision to remove or keep infected trees depends on lost productivity. We compared yield and vitality between infected and uninfected almond for cvs. Sonora and Nonpareil. Sonora was examined at three sites over 3 years and Nonpareil was examined at one site over 2 years. Yields of ALS-affected trees were significantly lower for both cultivars, although yield losses of Sonora were proportionally greater than those of Nonpareil. Yields of infected trees did not decline incrementally over years; rather, they fluctuated similarly to those of uninfected trees. In addition, no infected trees died during the course of the study. These results are in direct contrast to previous anecdotal reports which suggest that yields of infected trees incrementally decline and infected trees eventually die. A simple economic model was developed to determine conditions under which rouging infected trees would increase returns. Based on the model, orchard age, yield loss due to infection, and the value of a maximally producing almond tree should be considered when deciding to remove ALS-affected trees.

Sisterson, M. S., Ledbetter, C. A., Chen, J., Higbee, B. S., Groves, R. L., and Daane, K. M. 2012. Management of almond leaf scorch disease: Long-term data on yield, tree vitality, and disease progress. Plant Dis. 96:1037-1044. Almond leaf scorch disease (ALSD) has been a chronic problem for California almond growers. This disease is caused by the bacterial pathogen Xylella fastidiosa and is transmitted by xylem-feeding insects. Previous research suggested that retaining, rather than roguing, ALSD-affected trees may be more economically beneficial because ALSD-affected trees produced a reasonable yield and did not die over a 3-year period. Because almond orchards are kept in production for approximately 25 years, longer-term data are needed to fully evaluate the merits of retaining ALSD-affected trees. Extension of yield evaluations from 3 to 5 years demonstrated that yield loss due to ALSD was consistent over 5 years, with yields of ALSD-affected trees reduced by 20 and 40% compared with unaffected trees for ‘Nonpareil’ and ‘Sonora’, respectively. To assess risk of ALSD-affected trees serving as a source of inocula for secondary (tree-to-tree) spread and to evaluate vitality of ALSD-affected trees, previous surveys of two orchards were extended from 3 to 6 or 7 years. The relationship between disease incidence (percentage of trees infected) and survey year was linear for all cultivars examined at both orchards. Furthermore, at each orchard, the spatial location of infections detected after the first survey was random with respect to the spatial location of infections identified during the first survey, suggesting that ALSD-affected trees retained in orchards did not serve as a source for secondary spread. Over the 6- to 7-year study period, death of ALSD-affected trees was rare, with only 9% of ALSD-affected trees dying. Because orchards used in this study had relatively high disease incidence, 61 orchards containing Sonora were surveyed to determine typical levels of ALSD incidence. ALSD was widespread, with at least one infected tree in 56% of orchards surveyed, but incidence was typically low (mean incidence = 0.47%). Collectively, the results suggest that retaining ALSD-affected trees may be economically beneficial in older orchards.

Eighty-six almond accessions of diverse geographic origin, ranging from Central Asia to the USA, were genotyped in 15 simple sequence repeat (SSR) loci to compare genetic diversity parameters, characterize genetic differentiation, and examine factors responsible for the maintenance of genetic diversity and population structure in almond. The mean allele number was 18.86 alleles per locus. All but one primer demonstrated polymorphic information content higher than 0.7. Almond genotypes clustered according to their pedigree and geographic origin. STRUCTURE analysis determined nine genetically distinct subgroups within the studied genotypes including the Kyrgyz, Akdamar, Bademli, Hungarian, Monor, Italian, Moroccan, and Californian accessions and wild species and an admixed group. An AMOVA analysis confirmed that considerable genetic variation occurred within populations (71.30%), and genetic variation among populations was also significant (28.70%). The mean values of the fixation index (FST) varied between 0.38 and 0.55, indicating marked genetic differentiation among the populations. The among-population genetic differentiation based on allele sizes (RST) was significantly higher than that based on allele identities (FST) between the most groups, suggesting that stepwise mutations have also contributed to genetic differentiation. A Mantel test and a neighbor-joining tree showed no significant correlation between the geographic distance and the genetic distance (Rxy = 0.173, P = 0.226) and indicated that geographic distance among the assessed populations has little influence on their genetic differentiation (Rxy = 0.248, P = 0.194). Our data show drift, mutations, and massive gene exchange between several wild species and cultivated P. dulcis as crucial components of genetic differentiation. Slight losses of genetic diversity are attributable to geographic isolation, human selection and not to the relatively recent occurrence of self-compatibility. There was no indication of a major decrease in genetic variability in almond germplasm from Asia to Europe. The present results reveal that almond domestication avoided the occurrence of a genetic bottleneck although its risk is present in many subpopulations.

A 5-year field study was conducted to evaluate effects of duration and exclusion of Xylella fastidiosa infections on young almond tree performance and their links to tree vigor. ‘Nemaguard,’ ‘Okinawa,’ ‘Nonpareil,’ and Y119 were used as rootstocks for almond scion ‘Sonora.’ Among X. fastidiosa-infected trees, there was significant etiological heterogeneity with i) absence of leaf scorching symptoms in the presence of reduced growth, ii) presence of leaf scorching symptoms in the absence of reduced growth, and iii) severe leaf scorching and reduced growth. Trunk cross sectional areas of X. fastidiosa-infected trees grafted on ‘Nemaguard’ and ‘Nonpareil’ rootstocks were significantly smaller than noninfected trees, whereas trunk size of trees grafted on ‘Okinawa’ and Y119 was not affected by infection status. Severity of leaf scorching symptoms was highest on trees grafted on ‘Nonpareil’ rootstock, intermediate on ‘Okinawa’ and Y119, and lowest on ‘Nemaguard.’ X. fastidiosa infections and seasonal leaf scorching symptoms persisted on most inoculated trees throughout the study, except on trees grafted on ‘Nemaguard’ that manifested complete leaf scorching symptom remission and apparent elimination of the pathogen after the second year. Results indicate that depending on rootstock type X. fastidiosa can affect trunk size in a relatively short period and/or persist for years as trees grow.

Ten F2 clones from an initial hybridization of Prunus webbii × Prunus persica cv Harrow Blood were evaluated under greenhouse conditions for their reaction to Xylella fastidiosa subsp. fastidiosa strain M23 during two growing seasons. Clonal accessions used for the study were selected on the basis of horticultural diversity, and were a small subset of trees from a large F2 population. Foliar symptoms of M23-inoculated trees were monitored weekly throughout the 20-week growth period. Clones were then sampled for bacterial titer determinations. With the exception of parental accession Harrow Blood, all clones yielded measurable titer; however, almond leaf scorch disease symptoms were never observed in five of the ten sibling clonal accessions. Vegetative bud break and bloom phenology data collected from field-grown mother trees over a 7 year period as well as leaf morphology characters of the clonal accessions were examined for associations with bacterial titers of inoculated clones using a principal components analysis. No clear associations were noted, with small sample size limiting the predictive ability of the analysis.

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.

To facilitate development of Prunus L. rootstocks with desirable agronomic traits, domesticated peach (Prunus persica) and almond (P. dulcis) were crossed with wild almond relatives. This work reports that a hybrid from a P. webbii × P. persica cv. Harrow Blood cross is susceptible to almond leaf scorch disease (ALSD). ALSD is caused by the fastidious, xylem-limited bacterium Xylella fastidiosa. The P. webbii × ‘Harrow Blood’ hybrid, along with its parents, was inoculated with two ALSD-inducing strains (X. fastidiosa subsp. fastidiosa strain M23 and subsp. multiplex strain Dixon). Both X. fastidiosa strains grew to high titer in the susceptible P. webbii parent and in the interspecific hybrid; defoliation was also observed. As expected, ‘Harrow Blood’ did not exhibit defoliation symptoms or support growth of X. fastidiosa. This result contrasts with earlier work demonstrating that a P. persica × P. dulcis hybrid is not a suitable host for X. fastidiosa subsp. fastidiosa M23. It appears that the genetic basis of resistance/susceptibility differs between a P. persica × P. dulcis cross and the P. webbii × P. persica cross reported here. Understanding the degree of susceptibility to X. fastidiosa in complex hybrids of subgenus Amygdalus should be an important part of rootstock development.

More than 80% of the world's almonds are grown in California with several dozen almond cultivars available commercially. To facilitate promotion and sale, almond cultivars are categorized into marketing groups based on kernel shape and appearance. Several marketing groups are recognized, with the Nonpareil Marketing Group (NMG) demanding the highest prices. Placement of cultivars into the NMG is historical and no objective standards exist for deciding whether newly developed cultivars belong in the NMG. Principal component analyses (PCA) were used to identify nut and kernel characteristics best separating the 4 NMG cultivars (Nonpareil, Jeffries, Kapareil, and Milow) from a representative of the California Marketing Group (cultivar Carmel) and the Mission Marketing Group (cultivar Padre). In addition, discriminant analyses were used to determine cultivar misclassification rates between and within the marketing groups. All 19 evaluated carpological characters differed significantly among the 6 cultivars and during 2 harvest seasons. A clear distinction of NMG cultivars from representatives of the California and Mission Marketing Groups was evident from a PCA involving the 6 cultivars. Further, NMG kernels were successfully discriminated from kernels representing the California and Mission Marketing Groups with overall kernel misclassification of only 2% using 16 of the 19 evaluated characters. Pellicle luminosity was the most discriminating character, regardless of the character set used in analyses. Results provide an objective classification of NMG almond kernels, clearly distinguishing them from kernels of cultivars representing the California and Mission Marketing Groups. Practical Application A method to distinguish kernels from almond cultivars representing the Nonpareil, California, and Mission Marketing Groups was described. Kernels were categorized with less than 2% misclassification using multivariate statistics based on measurements involving weight, linear dimensions, and kernel skin color.

Dibromochloropropane was one of the primary chemical soil fumigants used to control nematodes. As a consequence, dibromochloropropane is now occurring widely in groundwater. This situation requires treating drinking water before human consumption because exposures to dibromochloropropane have shown linkage to infertility and circulatory system diseases. Here, activated biochar was produced from almond shells and used in the field to remove dibromochloropropane from a municipal water well. Results show that activated biochar removed 100 % of the dibromochloropropane for approximately 3 months and continued to remove it to below treatment standards for an additional 3 months. The breakthrough was modeled by a liquid film mass transfer model that described the experimental data very well. This manuscript reports on the efficient use of local resources such as almond shells to address local environmental needs.

Plants have an intriguing tripartite genetic system: Nuclear genome × Mitochondria × Plastids and their interactions may impact germplasm breeding. In grapevine, the study of cytoplasmic genomes has been limited, and their role with respect to grapevine germplasm diversity has yet to be elucidated. In the present study, the results of an analysis of the cytoplasmic diversity among 6073 individuals (comprising cultivars, interspecific hybrids and segregating progenies) are presented. Genotyping by sequencing (GBS) was used to elucidate plastid and mitochondrial DNA sequences, and results were analyzed using multivariate techniques. Single nucleotide polymorphism (SNP) effects were annotated in reference to plastid and mitochondrial genome sequences. The cytoplasmic diversity identified was structured according to synthetic domestication groups (wine and raisin/table grape types) and interspecific-hybridization-driven groups with introgression from North American Vitis species, identifying five cytoplasmic groups and four major clusters. Fifty-two SNP markers were used to describe the diversity of the germplasm. Ten organelle genes showed distinct SNP annotations and effect predictions, of which six were chloroplast-derived and three were mitochondrial genes, in addition to one mitochondrial SNP affecting a nonannotated open reading frame. The results suggest that the application of GBS will aid in the study of cytoplasmic genomes in grapevine, which will enable further studies on the role of cytoplasmic genomes in grapevine germplasm, and then allow the exploitation of these sources of diversity in breeding.

Management of almond leaf scorch disease requires knowledge of all possible infection pathways. The disease is caused by the xylem-limited bacterium Xylella fastidiosa, which is transmitted by several species of sharpshooters. The objectives of this research were to elucidate the fate of bacteria in planta after inoculations in almond nursery plants and to determine patterns of insect vector population dynamics and temporal distribution of X. fastidiosa–infected plants relative to host plant assemblages in habitats surrounding commercial nurseries. In an experimental nursery, disease incidence was markedly affected by rootstock type. Prior to bud grafting, ‘Nemaguard’ rootstock seedlings were not susceptible to bacterial infection. After bud grafting with a susceptible scion (‘Sonora’), scions were susceptible to infection regardless of rootstock genotype. Surveys near commercial nurseries revealed that only habitats with permanent grass cover sustained vector populations throughout the season. A total of 87 plant samples tested positive for X. fastidiosa (6.3%) using enzyme-linked immunosorbent assay (ELISA), with a higher number of X. fastidiosa–infected plants found in weedy alfalfa fields than in other habitat types. Among plant species infected by X. fastidiosa, 33% were winter annuals, 45% were biennials or perennials, and 22% were summer annuals. Collectively, these findings identified a potential pathway for X. fastidiosa infection of almonds in nursery situations.

A multiyear study was conducted in California's San Joaquin Valley to examine variability of carpological characteristics of the popular Nonpareil almond cultivar. Samples of ‘Nonpareil’ almond fruit were collected from a single orchard during seven consecutive harvests and evaluated for 19 specific carpological characters. Harvest year significantly affected all measured variables. Of the evaluated characters, fruit weight was the most variable between years, whereas kernel percentage was one of the least variable characters. As a result of year-to-year variability in carpological characters, the relationship between kernel weight and all other measured variables was investigated to determine if regression models could better describe kernels. Kernel weight best explained variability in kernel surface area (R2 = 0.943) with year-to-year variability having only a minor affect on the relationship. The results indicate that ‘Nonpareil’ almonds cannot be described using simple metrics and that definitive metrics must be able to account for differences among years.

A series of laboratory and field studies were conducted using three lines of navel orangeworm, Amyelois transitella (Walker) (Lepidoptera: Pyralidae), reared on wheat bran diet and almonds, Prunus dulcis (Mill.) D.A.Webb, at constant and fluctuating temperature. The duration of development on wheat bran diet at constant temperature differed significantly among the three lines. Development was as much as 40% faster at constant temperature than at fluctuating temperatures, consequently the developmental duration determined at constant temperature was not an absolute measure. When the maximum temperature in fluctuating regimes exceeded 43 degrees C, survival decreased by 50% compared with the constant temperature control. In almonds held at constant temperature, the developmental rate on new-crop nuts was variety-dependent and was fastest on 'Nonpareil' almonds and slowest on the experimental selection '23-122'. Development and survival were also variety-dependent on unharvested (mummy) almonds, and navel orangeworm average emergence was earliest from Nonpareil and latest from 'Carmel' nuts, differing by 529 degree-days, whereas survival was the highest on 'Butte', 35.7%, and the lowest on Carmel nuts, 7.2%. In our trials, both the speed of development and survival depended on host age, variety and quality, indicating that almonds were a dynamic rather than a static nutrient source for navel orangeworm. Identifying the factors responsible for variation in development and survival will give insight into improving control strategies.

Steam-activated carbons were made from shells from five different almond varieties (‘Nonpareil,’ ‘Padre,’ Tuono,’ ‘23-122,’ and ‘Y120-74′) and from a mix of almond types. The purpose of the work was to evaluate if the composition of shells had any effect on the performance of the final product. The shells contained the same level of cellulose, but differed in their lignin and hemicellulose composition. The yield of carbon from the shells ranged from 20% to 23.5%, indicating a loss of about 80% of initial mass. Regardless of the composition, the performance of the activated carbons made from the shells was very similar in a feasibility study. The carbons were found to have a capacity of 100–105 mg/g of carbon for the two contaminants tested (dibromochloropropane and trichloroethylene). The finding that the activated carbons performed equally well, regardless of source of almond shells, suggest that that carbons could be made from almonds shells with consistent quality.

Seedling peach (Prunus persica Batsch) and clonal peach–almond hybrids are popular rootstock choices for commercial almond growers in California. In this study, clonal replicates of peach and almond [P. dulcis (Mill.) D.A. Webb] rootstock germplasm and a first-generation peach–almond hybrid created from them were challenged with Xylella fastidiosa isolate M23. Clonal replicates were needle-inoculated with M23 and maintained in a greenhouse environment for a growing season. Typical almond leaf scorch disease symptoms began to develop on M23-inoculated almonds 11 weeks after inoculation. No leaf scorch symptoms were observed on M23-inoculated peach or peach–almond hybrids. Quantitative real-time polymerase chain reaction revealed consistent levels of X. fastidiosa DNA among inoculated almond replicates, whereas X. fastidiosa DNA was undetectable in replicates of peach–almond hybrids. A trace level of X. fastidiosa DNA was detected in a single peach replicate, and statistical analysis demonstrated that this level differed significantly (P < 0.001) from that detected in almond replicates. Selected almonds were further sampled sequentially along their meristematic axes to examine bacterial titer throughout the trees. Selected almond trees differed significantly (P = 0.036) in bacterial titer, but no significant differences were noted in levels of X. fastidiosa from different vertical sections of the main growth axes. The results suggest that peach and peach–almond hybrid rootstock germplasm used by commercial almond tree nurseries in California are not primary inoculum sources for X. fastidiosa-induced diseases.

For decades, seedling peaches have been used as the standard rootstock in California almond orchards. Vigorous, deep rooted trees are needed in almond orchards for maximum yields and to withstand the annual tree-shaking at harvest. Currently, researchers are actively evaluating rootstocks for almonds in field trials and in various screening protocols. In this study, seedling rootstocks, obtained from male-sterile advanced generation peach-almond (PEAL) hybrid mother trees, were compared with ‘Nemaguard’ peach seedlings for emergence in the nursery row, trunk caliper at propagation time, and end of season dormant above ground tree weight. Seedling emergence was affected significantly (P ≤ 0.05) by seed source, as was trunk caliper and end of season dormant above ground tree weight. Trunk caliper and dormant above ground tree weight were also affected significantly (P ≤ 0.05) by planting year. Results obtained in this study demonstrate the enhanced first year growth from seedlings of advanced generation PEAL hybrids, as compared to ‘Nemaguard’ seedlings. Seedling emergence in the rootstock bed was not affected significantly by planting year. Advanced generation PEAL hybrid seedlings were ready for June-budding at an earlier date compared to ‘Nemaguard’ seedlings, providing the potential for larger-sized finished nursery stock by the end of the growing season. Due to the male-sterile status of the advanced generation PEAL mother trees, bloom periods of several root-knot nematode resistant rootstock cultivars were examined for their degree of synchronicity with the mother trees. The examined rootstocks and mother trees varied in both chill hour and post-chill heat requirements necessary to effect bloom. ‘Flordaguard’ peach rootstock began bloom in advance of the male-sterile mother trees, whereas the bloom period of ‘Tsukuba No. 4’ occurred well after, suggesting they would not be effective synchronous pollenizers for consistent hybrid seed production. Based on more limited flowering period data, better bloom synchronicity was achieved with a Tsukuba No. 4 X Flordaguard hybrid.

The use and disposal of biosolids, or wastewater treatment sludge, as a fertilizer and soil amendment is becoming increasingly widespread. We evaluated the multiyear use of biosolids in apricot (Prunus armeniaca L.) production, grown on productive agricultural soils. Class A biosolids were initially applied annually at rates of 0, 1.9, 5.8, and 11.7 Mg · ha−1 (dry basis) to a 2‐year‐old apricot orchard on the USDA‐ARS research site on the eastern side of the San Joaquin Valley, CA. These application rates provided estimated rates of 0 (control), 57, 170, and 340 kg total N · ha−1 yr−1, respectively. Compared to the control treatment, the applications of biosolids significantly increased soil salinity (electrical conductivity from 1:1 soil–water extract) and total concentrations of nutrients [e.g., calcium (Ca), magnesium (Mg), sulfur (S), phosphorus (P), zinc (Zn), and copper (Cu)] after 7 years but did not increase the concentrations of selected metals [cadmium (Cd), chromium (Cr), cobalt (Co), ...

Kernels of ‘Nonpareil’ almond and advanced breeding selections 23.5–16 and 23–122 were evaluated for similarities and differences in commercially important kernel characteristics. These three almond types did not differ in kernel mass, kernel length and width, nor in kernel color coordinates, luminosity and hue. ‘Nonpareil’ kernels were observed to be significantly (p ⩽ 0.05) thicker than kernels of 23.5–16 and 23–122. Chroma value of ‘Nonpareil’ kernels was significantly higher (p ⩽ 0.05) than that of 23–122, but did not differ from that of 23.5–16. Bulk in-shell samples of the three almond types were then compared after a mechanical cracking treatment using identical roller settings in a research-sized commercial cracking machine. Sticktight content varied significantly (p ⩽ 0.01) amongst the three almond types prior to cracking bulked samples. The cracking treatment significantly reduced (p ⩽ 0.01) sticktight content in each of the almond samples and a significant interaction (p ⩽ 0.01) was observed between almond types and cracking treatment with regard to sticktight content. ‘Nonpareil’ and 23.5–16 did not differ in sticktight content either prior to or after the cracking treatment. The three almond types varied significantly (p ⩽ 0.05) in the various categories of edible kernels (whole, double, scratched, broken & chipped) after the cracking treatment.

The pellicle or seed coat of almond kernels is subject to darkening during long-term storage and may affect the marketability of the stored product. Environmental conditions during storage and genetic factors both affect the extent of darkening during the storage period. The degree of pellicle color change of five distinct almond accessions was examined during long-term storage at 2, 22 and 32 ◦ C. Pellicle luminosity, chroma and hue angle were measured on 12 dates throughout an 11-month storage period. An ANCOVA was used, with storage temperature being a covariate, to examine the relative differences in luminosity, chroma and hue angle during the storage progression. A comparison of weighted simple linear regression equations was used to distinguish between different rates of pellicle color coordinate degradation during the storage period. When averaged across the three storage temperatures, almond accession Padre consistently had significantly lower pellicle luminosity and chroma values throughout the storage period as compared with the other four almond accessions (p ≤ 0.05). While pellicle hue angle values of Padre were significantly lower than those of Nonpareil at the start of the test (p ≤ 0.05), Nonpareil’s pellicle hue angles were significantly lower than those of Padre at the end of the storage period (p ≤ 0.05). Almond accession Nonpareil had the largest percentage decrease of the five almond accessions for pellicle luminosity (36.9%) and hue angle (12.5%). Regression analysis revealed significant differences in degradation rates of pellicle luminosity and chroma at all three storage temperatures (p ≤ 0.05), but significant differences in pellicle hue angle degradation were only evident at the lowest storage temperature (p ≤ 0.05). Published by Elsevier B.V.

Central Asian apricot germplasm was used in hybridizations with California adapted apricots to increase Brix levels and improve fresh eating quality. Fruit from parental trees, the F1 hybrid and two backcross families were evaluated for fruit quality traits and analyzed by HPLC for specific sugar content. The F1 hybrid between Central Asian and California adapted apricots was intermediate to its parents in many of the evaluated characteristics and levels of specific sugars. When the F1 hybrid was backcrossed to California adapted apricots ‘Lorna’ and ‘Robada,’ the resulting hybrids were diverse in Brix, juice acidity, fruit size and profiles of specific sugars. Glucose: fructose ratios higher that 3.3 were encountered in fruit from five of the 22 analyzed seedlings, and fructose: sorbitol ratio ranged from 0.67 to 6.46. Brix and total sugar content correlated significantly with each other and with both sucrose and glucose. No significant correlations existed between sorbitol and any of the other analyzed sugars, nor with Brix or total sugars. The results demonstrated the extent of sugar profile modification possible in California adapted apricots after just two generations of breeding with Central Asian apricot germplasm.

Nine Prunus accessions were evaluated for germination and plantlet growth in an in vitro osmotic screening test using mannitol as an osmoticum. Embryos from diverse peaches, almonds and peach-almond hybrids were cultured in Woody Plant Medium, and in this same medium modified with the inclusion of 350 mM mannitol. Embryos were stratified in vitro for 60 days, induced to germinate for a two week period and then allowed to develop and grow for another 20 days prior to harvest. Fresh weights of both roots and shoots as well as percent germination were recorded at harvest. The main effects of nutrient medium, germplasm type (peach, peach-almond, almond) and specific Prunus accession were all highly significant (P = 0.01) with regard to fresh weight of roots and shoots. Embryo germination was affected significantly by the inclusion of mannitol in the nutrient medium and by the particular germplasm type (P=0.01 and P=0.05, respectively). Significant interactions of nutrient medium × Prunus accession and nutrient medium × germplasm type were also detected for both root and shoot fresh weights. Almond germplasm cultured in Woody Plant Medium with 350 mM mannitol produced significantly more roots and shoots than either peaches or peach-almond hybrids grown in the same medium. Peach-almond hybrid embryos were observed to germinate at a significantly higher frequency than peach embryos when averaged across both media. Results obtained in this study indicate a wide range of average plantlet fresh weight relative to the specific germplasm challenged in the osmotic screen.

Optimum fruit quality depends upon a number of factors, including fruit developmental stage at harvest. The volatile constituents present in apricot fruit and plumcot accession P251-002 during three different developmental stages have been studied, as well as some physical characteristics such as weight, firmness, °Brix, titratable acidity and flesh and skin colour. The volatile compounds behaved differently during the fruit maturation period, alcohols being the most important group, quantitatively, during the three developmental stages in apricot fruit. In plumcot, total volatiles obtained from fruit sample extractions were very similar in each developmental stage; however, the aromatic profile of constituents changed as fruit maturity progressed to a tree ripe stage. Important differences were found in the volatile constituents profile for both fruits; at the tree ripe stage, the concentration of lactones and terpenic alcohols, characteristic compounds of apricot aroma, were much higher in apricot than plumcot, the latter more resembling a plum aromatic profile. Even with the important presence of lactones that gives a very aromatic apricot when tree ripe, the low firmness at this point does not allow any commercial use of the fruit. © 1997 SCI

Four experimental apricot selections and four commercial apricot cultivars were evaluated for various physical and chemical characteristics. The eight apricot accessions were divided into three categories based upon their average dates of fruit maturation (based on flesh firmness) in California's San Joaquin Valley. Within maturity groups, apricot accessions evaluated in this study had diverse fruit weight, Brix, titratable acidity, and color of both flesh and skin. Profiles of volatile constituents extracted from the eight accessions did not follow any consistent pattern. Alcohols, however, were the dominant group of volatiles present in each sample, and linalool was highest within each profile. The results obtained from this research demonstrate that several of the experimental apricot selections had better fruit size, Brix and fruit color characteristics than commercial apricot cultivars of the same fruit maturity in the same ripening season.

More than 80% of the world's almonds are grown in California with several dozen almond cultivars available commercially. To facilitate promotion and sale, almond cultivars are categorized into marketing groups based on kernel shape and appearance. Several marketing groups are recognized, with the Nonpareil Marketing Group (NMG) demanding the highest prices. Placement of cultivars into the NMG is historical and no objective standards exist for deciding whether newly developed cultivars belong in the NMG. Principal component analyses (PCA) were used to identify nut and kernel characteristics best separating the 4 NMG cultivars (Nonpareil, Jeffries, Kapareil, and Milow) from a representative of the California Marketing Group (cultivar Carmel) and the Mission Marketing Group (cultivar Padre). In addition, discriminant analyses were used to determine cultivar misclassification rates between and within the marketing groups. All 19 evaluated carpological characters differed significantly among the 6 cultivars and during 2 harvest seasons. A clear distinction of NMG cultivars from representatives of the California and Mission Marketing Groups was evident from a PCA involving the 6 cultivars. Further, NMG kernels were successfully discriminated from kernels representing the California and Mission Marketing Groups with overall kernel misclassification of only 2% using 16 of the 19 evaluated characters. Pellicle luminosity was the most discriminating character, regardless of the character set used in analyses. Results provide an objective classification of NMG almond kernels, clearly distinguishing them from kernels of cultivars representing the California and Mission Marketing Groups.

Significant growth differences (p≤

Volatile compounds of two plum species (Prunus salicina Lindl and Prunus simonii L) were analyzed by capillary gas chromatography-mass spectrometry using simultaneous vacuum distillation extraction. Aroma patterns were identified and quantified. A total of 60 compounds were identified, of which 23 were unique to P simonii. The profile of P simonii, as well as a study of the odor unit values of some identified compounds, indicated a much stronger aroma than P salicina. Hexyl acetate, which produces a characteristic apple aroma, was present in P simonii at levels 50-fold higher than in the studied cultivars of P salicina.

Apricot (Prunus armeniaca L.) embryos at three stages of development were cultured on C2d, SBH and WPM media. In vitro culture produced high percentages of germination and seedlings throughout all three developmental stages. Significant media effects were noted for changes in both embryo length and weight during the culture period, as well as number of plants produced. Embryos between 5 and 9 mm (developmental stage I) germinated and developed into plants in a significantly higher percentage than in the other two more mature stages. Therefore, embryo culture can be successfully used as a tool in an apricot breeding program to obtain higher percentages of seedlings from planned hybridization or to overcome a lack of seed germination.

The volatile components of fresh, tree-ripened apricots (Prunus armeniaca L.), plums (Prunus salicina Lindl.), and their interspecific hybrids were isolated by simultaneous distillation extraction and analyzed by gas chromatography-mass spectrometry. The study of the aromatic profiles of the parents (apricot and plum) and the progenies (plum×apricot) demonstrated that the progeny retained the ability to produce volatile compounds typical of the parents and that components important to the aromas and flavors of the parents were produced at high levels

To manage appropriately the clinical care of their patients, clinicians must simultaneously consider information from a number of sources: a. The health history of the patient and the patient’s family. b. The current health problems of the patient. c. The clinical status of the patient including laboratory and other physiological results. d. The current treatment regimen and the patient’s individual response to selected treatment options. e. A body of knowledge concerning diagnostic possibilities and their treatment recommendations. f. Evidence about the efficacy and risks of the various treatment options. g. The expected outcomes and prognosis of patients with similar health problems, clinical status, and treatment regimen. h. A large body of general scientific and medical knowledge that facilitates the understanding and interpretation of all this information.

Tree characteristics Trees of ‘Apache’ are upright in branch growth habit and demonstrate extremely strong vigor as compared with reference cultivars (Guerriero and Watkins, 1984). As such, ‘Apache’ trees can be pruned easily and appropriate 1-year-old wood selected for continuous renewal of fruiting spurs. The upright growth habit makes ‘Apache’ suitable for both trellised and traditional nonsupported tree planting arrangements. Fruit production of ‘Apache’ occurs on both fruiting spurs and along 1-year-old shoots. Larger fruit sizes are always obtained from those fruit that developed on spurs as opposed to 1-year-old shoots. The branch growth habit of ‘Kettleman’ is much more spreading as compared to ‘Apache.’ Like ‘Apache,’ ‘Kettleman’ trees exhibit extremely strong vigor, and are also easy to prune. Fruiting spurs are easily replenished from the large supply of annual shoots present throughout the tree. Both 1-year-old shoots and spurs are fruitful with largest fruit developing from the strongest spurs. ‘Kettleman’s’ spreading growth branch habit makes the tree most suitable for an open vase tree form. ‘Apache’ and ‘Kettleman’: Two Early Season Apricots for the Fresh Market Craig A. Ledbetter and Sharon J. Peterson U.S. Department of Agriculture, Agricultural Research Service, San Joaquin Valley Agricultural Sciences Center, Crop Diseases, Pests and Genetics Research Unit, 9611 South Riverbend Avenue, Parlier, CA, 93648-9757

Clonal replicates of Prunus dulcis cv ‘Butte,’ P. webbii and their interspecific hybrid P 63-61 were inoculated with Xylella fastidiosa strain M23 and evaluated for almond leaf scorch disease and subsequent winter curing of infections during three growing seasons. Initial inoculations established greater than 90% infection in each of the accessions, based on PCR diagnoses from petiole tissues sampled near the inoculation site. Classic leaf scorch symptoms were evident in each population during the first growing season in a controlled greenhouse environment. Trees were removed from the greenhouse during the winters to accumulate chill hours and to provide the possibility of winter curing X. fastidiosa infections. Both PCR diagnostics and in vitro cultivation were used during the second and third growing seasons to determine the persistence of X. fastidiosa in clones among the three populations. Tree survival and the degree of winter cured infections differed among the three populations, with P. webbii and P 63-61 demonstrating enhanced levels of survivorship over ‘Butte.’ After two cycles of ambient winter temperatures and subsequent growth, ‘Butte’ averaged 21.2% winter cured trees with 73.1% mean survival. Tree survival and winter cured infections were nearly 100% for both P. webbii and P 63-61, demonstrating the utility of P. webbii in almond breeding efforts aimed at reducing tree vulnerability to X. fastidiosa infections.