California Olive Research Articles

Field evaluation of fungicides for the management of Neofabraea leaf lesion of olive in California.

Field experiments were conducted during the fall-winter seasons of 2017-18 and 2018-19 to evaluate the efficacy of various fungicides to control Neofabraea leaf lesion of olive. Field trials were conducted in the highly susceptible cultivar Arbosana in a commercial, super-high-density orchard in San Joaquin County, California. Up to eight fungicidal products were applied using an air blast backpack sprayer and their efficacy was compared with different application strategies. Results showed that most products were effective in reducing infection by the pathogens and limiting disease severity. Overall, best disease control was achieved by thiophanate-methyl, cyprodinil, difenoconazole + cyprodinil, and chlorothalonil, providing up to 75% reduction in disease severity. Copper hydroxide did not control the disease. In 2018-19, the fungicides difenoconazole + cyprodinil and ziram were evaluated in additional field trials using different application strategies (single, dual, and combined applications) suitable for pathogen resistance management. Results showed that both products provided significant reduction in disease severity (~50%) although no differences in efficacy were found between the two products nor between the different application strategies. Both products performed equally using one or two applications at two-week interval following harvest.

Extraction, Purification and In Vitro Antioxidant Activity Evaluation of Phenolic Compounds in California Olive Pomace

Olive pomace (OP) is a valuable food byproduct that contains natural phenolic compounds with health benefits related to their antioxidant activities. Few investigations have been conducted on OP from the United States while many studies on European OP have been reported. OP of Arbequina, the most common cultivar from California, was collected and extracted by water, 70% methanol and 70% ethanol, followed by purification using macroporous absorbing resin. Results showed that the extractable total phenolic content (TPC) was 36–43 mg gallic acid equivalents (GAE)/g in pitted, drum-dried defatted olive pomace (DOP), with major contributions from hydroxytyrosol, oleuropein, rutin, verbascoside, 4-hydroxyphenyl acetic acid, hydroxytyrosol-glucoside and tyrosol-glucoside. Macroporous resin purification increased TPC by 4.6 times the ethanol crude extracts of DOP, while removing 37.33% total sugar. The antioxidant activities increased 3.7 times Trolox equivalents (TrE) by DPPH and 4.7 times TrE by ferric reducing antioxidant power (FRAP) in the resin purified extracts compared to the ethanol crude extracts. This study provided a new understanding of the extraction of the bioactive compounds from OP which could lead to practical applications as natural antioxidants, preservatives and antimicrobials in clean-label foods in the US.

Olea europaea geminivirus is present in a germplasm repository and in California and Texas olive (Olea europaea L.) groves.

Olea europaea geminivirus (OEGV) from olive accessions in Italy was characterized recently. OEGV was also detected during routine high-throughput sequencing screening of olive (cv. Leccino) material, and its complete bipartite genome segments were sequenced and shown to be 100% identical to those of the isolate from Italy. Using two pairs of newly designed primers targeting the AV1 and BV1 genes, OEGV was detected in randomly sampled olive trees from the U.S. Department of Agriculture National Clonal Germplasm Repository (USDA-NCGR) (21.4% or 6/28), commercial and residential settings in California (47.6% or 10/21), and an orchard in Texas (60% or 30/50). The cuttings for the USDA-NCGR-positive trees originated from the former Serbia and Montenegro, Spain, Italy, and Greece. Comparative analysis of the directly sequenced gene fragments from randomly selected samples showed that OEGV isolates from the different sources were 100% identical to each other. The results indicate that OEGV spread was likely facilitated by inadvertent movement of contaminated olive germplasm.

Olive Twig and Branch Dieback in California Caused by Cytospora oleicola and the Newly Described Species Cytospora olivarum sp. nov.

Field surveys conducted throughout California olive-growing regions in 2008 and 2009 resulted in a collection of 101 Cytospora-like isolates from olive twig and branch dieback symptoms. Cytospora isolates were isolated from multiple cvs. in different olive orchards in Fresno, Madera, Merced, Napa, Riverside, Santa Barbara, Sonoma, Tulare, and Ventura counties. Taxonomic studies of macro- and microscopic structures along with multigene phylogenetic analyses of the internal transcribed spacer region, including the 5.8S rDNA (ITS1-5.8S-ITS2), and fragments of the translation elongation factor 1-α, beta-tubulin, and actin genes identified two species, Cytospora oleicola and C. olivarum sp. nov. Pathogenicity studies conducted in mature olive trees cvs. Manzanillo and Sevillano showed both species to be pathogenic and able to cause vascular necrosis and cankers in olive branches. This study adds to the current knowledge on the etiology of olive twig and branch dieback and provides new important information for the development of effective control strategies against canker diseases affecting olive in California.

Current Distribution of the Olive Psyllid, Euphyllura olivina, in California and Initial Evaluation of the Mediterranean Parasitoid Psyllaephagus euphyllurae as a Biological Control Candidate.

The olive psyllid, Euphyllura olivina, is a newly invasive species to California with the potential to become an economical pest if it reaches the olive production regions of California’s Central Valley. Here, we report on surveys undertaken in California to assess the psyllid’s current distribution and the occurrence of parasitism. Additionally, we present results of foreign collections of its parasitoids and initial non-target studies of a possible biological control agent, the Mediterranean parasitoid Psyllaephagus euphyllurae. The current distribution of the psyllid appears to be limited to the California coast between Monterey and San Diego; there have been no reports of infestations on olives in the major production areas of central and northern California. Psyllaephagus euphyllurae was the major primary parasitoid found in our foreign collections. The potential non-target impact of P. euphyllurae was tested on three native North American psyllid species: Neophyllura arctostaphyli, Euglyptoneura nr. robusta, and Calophya nigrella. No P. euphyllurae developed on the non-target species during no-choice tests. Behavioral observations in choice tests confirmed no attack on the non-target hosts, although the parasitoid did remain longer on N. arctostaphyli-infested manzanita plants, and revealed no host feeding behavior.

Identification and Characterization of Neofabraea kienholzii and Phlyctema vagabunda Causing Leaf and Shoot Lesions of Olive in California.

California produces over 95% of the olives grown in the United States. In 2017, California's total bearing acreage for olives was 14,570 hectares producing 192,000 tons of olives valued at $186.6 million. During the early spring of 2016, unusual leaf and shoot lesions were detected in olive trees from superhigh-density orchards in the Northern San Joaquin and Sacramento valleys of California. Affected trees displayed numerous leaf and shoot lesions developing at wounds created by mechanical harvesters. The 'Arbosana' cultivar was highly affected by the disease, whereas the disease was sporadic in 'Arbequina' and not found in 'Koroneiki' cultivar. Two fungal species, Neofabraea kienholzii and Phlyctema vagabunda, were found to be consistently associated with the disease, and Koch's postulates were completed. Species identity was confirmed by morphology and molecular data of the partial large subunit rDNA, the internal transcribed spacer region, and partial beta-tubulin region. The disease signs and symptoms are described and illustrated.

The Effects of Variety, Growing Region, and Drought Stress on Fatty Acid and Sterol Compositions of California Olive Oil

AbstractA total of 297 single‐varietal olive oil samples collected from four California regions (Central Valley, Wine Country, South Coast, and Desert) were analyzed on the fatty acid (FA) and sterol compositions between 2010 and 2017. Significantly higher amounts of palmitic acid (PAM), palmitoleic acid, and total sterols were detected in varieties including Arbequina, Arbosana, Picual, Leccino, and Koroneiki from the Desert region. Two super‐high density varieties Arbequina and Koroneiki from the Desert region had a significantly higher campesterol content (5.3 ± 0.2 and 4.7 ± 0.1%, respectively) compared to the same varieties from the Wine Country and the South Coast, not meeting the limit of the existing California olive oil standards [Correction added on 8 March 2019 after first online publication: the preceding sentence has been updated to reflect the correct campesterol content.]. The impact of severe droughts in California during late 2011 and 2014 on the major FA and sterol compositions of California olive oil was also analyzed. Multivariate chemometrical tools, one‐way ANOVA and principle component analysis (PCA), confirmed the significant differences between samples from the Desert region and other growing regions among several varieties and achieved desirable segregation on the PCA biplots for variety‐region classification. This study demonstrates a feasible approach of olive oil composition database establishment for new olive‐growing regions; the proposed chemometrical method can be used to characterize unknown variety of olive oils produced from different regions in California; and the collected FA and sterols data provide information for revision recommendations to the current olive oil standards.

An Experimental Test of the Host-Plant Range of Nonrecombinant Strains of North American Xylella fastidiosa subsp. multiplex.

Nonrecombinant strains of Xylella fastidiosa subsp. multiplex (those lacking evidence of significant intersubspecific homologous recombination) infect the xylem of a wide range of native and nonnative trees in North America. However, the degree to which different strains have a specialized host range remains poorly understood. We tested eight strains isolated from five different tree species (almond, olive, sweetgum, and plum in California and oak in Washington, DC). Experiments were conducted in greenhouses in Riverside, CA, and each strain was tested on 11 to 15 of the 17 plant species tested. Hosts infected by the most strains were plum (5 of 8 strains) and almond (4 of 8), while their congener peach was only infected by 1 of 8. No strains infected oleander or mulberry. All strains successfully infected their original host, with peach, olive (1 of 7), and sweetgum (2 of 6) only infected by such strains. Of the 90 total strain-novel-host combinations tested, 11 resulted in unambiguous infection, 2 gave ambiguous results, and the remaining 77 failed to result in symptoms or bacterial spread. All eight strains had a unique host range, including two pairs of strains with the same multilocus sequence typing sequence type, providing strong evidence of extensive plant-host specialization. There was little evidence that host relatedness was driving host specificity.

Molecular phylogeny of Cytospora species associated with canker diseases of fruit and nut crops in California, with the descriptions of ten new species and one new combination

Cytospora species are destructive canker and dieback pathogens of woody hosts in natural and agroecosystems around the world. In this genus, molecular identification has been limited due to the paucity of multi-locus sequence typing studies and the lack of sequence data from type specimens in public repositories, stalling robust phylogenetic reconstructions. In most cases a morphological species concept could not be applied due to the plasticity of characters and significant overlap of morphological features such as spore dimensions and fruiting body characters. In this study, we employed a molecular phylogenetic framework with the inclusion of four nuclear loci (ITS, translation elongation factor 1-alpha, actin, and beta-tubulin) to unveil the biodiversity and taxonomy of this understudied important genus of plant pathogens. Phylogenetic inferences based on 150 Californian isolates revealed 15 Cytospora species associated with branch and twig cankers and dieback of almond, apricot, cherry, cottonwood, olive, peach, pistachio, plum, pomegranate, and walnut trees in California. Of the 15 species recovered in this study, 10 are newly described and typified, in addition to one new combination. The pathogenic status of the newly described Cytospora species requires further investigation as most species were associated with severe dieback and decline of diverse and economically important fruit and nut crops in California.

Comparative genomics of the Erwinia and Enterobacter olive fly endosymbionts

The pestivorous tephritid olive fly has long been known as a frequent host of the obligately host-associated bacterial endosymbiont, Erwinia dacicola, as well as other facultative endosymbionts. The genomes of Erwinia dacicola and Enterobacter sp. OLF, isolated from a California olive fly, encode the ability to supplement amino acids and vitamins missing from the olive fruit on which the larvae feed. The Enterobacter sp. OLF genome encodes both uricase and ureases, and the Er. dacicola genome encodes an allantoate transport pathway, suggesting that bird feces or recycling the fly’s waste products may be important sources of nitrogen. No homologs to known nitrogenases were identified in either bacterial genome, despite suggestions of their presence from experiments with antibiotic-treated flies. Comparisons between the olive fly endosymbionts and their free-living relatives revealed similar GC composition and genome size. The Er. dacicola genome has fewer genes for amino acid metabolism, cell motility, and carbohydrate transport and metabolism than free-living Erwinia spp. while having more genes for cell division, nucleotide metabolism and replication as well as mobile elements. A 6,696 bp potential lateral gene transfer composed primarily of amino acid synthesis and transport genes was identified that is also observed in Pseudomonas savastanoii pv savastanoii, the causative agent of olive knot disease.

Fungal trunk diseases: a problem beyond grapevines?

Grapevine trunk diseases (GTDs) are caused by a broad range of taxonomically unrelated fungi that occur wherever grapes are grown and are the main biotic factor limiting vineyard productivity and longevity (Bertsch et al., 2013). GTDs cause untenable economic losses to the grapevine industry worldwide. For example, they are considered a ‘national crisis’ in France, where it has been estimated that 12% of the vineyards are currently economically nonviable due to these maladies causing losses of about €1 billion (Lorch, 2014). Because GTDs are chronic and there is currently no option to eradicate the infections, unproductive vineyards must be replanted, at a worldwide annual cost estimate of €1·132 billion (Hofstetter et al., 2012). The establishment, progress, severity and spread of GTDs have been associated with (i) drought, (ii) limited availability of effective fungicides, (iii) pressure to increase yields, (iv) lack of pruning wound protection due to cost of labour, and/or (v) poor low-quality propagation material. Growers are demanding solutions. Many vineyards with high GTD incidence were planted in the mid-to-late 1990s, during which wine-grape prices were increasing (Volpe et al., 2008). These vineyards were being replanted in the wake of phylloxera, and nurseries could barely meet the demand for grape plants. In 2009 researchers declared the worldwide impact of GTDs and prioritized research goals (Bertsch et al., 2009). Despite scientific advances, there are still unanswered questions, for example about how the pathogens spread and which climate conditions favour infection. This limits the efficacy of GTD management practices. Other crops, such as almond, pistachio and walnut, are now experiencing planting booms (INC, 2015). The significance of these and other tree crops is that they host some of the same GTD pathogens. While researchers fine-tune strategies for managing GTDs in grape, the pathogens may alternate to tree crops, thus endangering the productivity and longevity of orchards and vineyards alike. Recent reports of high disease incidence in pome and stone fruits, nut crops, small fruits and olive in California (Úrbez-Torres et al., 2013), Iran (Mohammadi et al., 2015), Italy (Carlucci et al., 2015), South Africa (Cloete et al., 2011) and Spain (Gramaje et al., 2012) highlight the need for a focus on this new set of hosts. The production systems are different; not all practices for GTD management in grape are feasible in tree crops, especially with dwindling numbers of skilled farm labourers. Tree crop nurseries are struggling to meet demands for plant material and, from our experience with GTDs, a lack of first-quality plants means that low-quality plants are sold, too. Are these plantings doomed to a lifetime of poor productivity? Is the sustainability of the fruit and tree nut industries at risk? Yours sincerely, David Gramaje et al.

New Missionaries

Featuring a wide cast of players, from small-scale family-owned operations to large corporate enterprises, Flacks reports on contemporary olive oil production in California, presenting historical information, photos, and legislative testimony. Recent efforts to establish a mature California olive industry and standards, including those of the UC Davis Olive Center, the California Olive Oil Council, and state Senator Lois Wolk are described. The involvement of Spaniards in California olive oil production, from the earliest days of the state’s history, to current efforts to expand super high density olive groves, is highlighted.

Direct Measurement of Oleocanthal and Oleacein Levels in Olive Oil by Quantitative 1H NMR. Establishment of a New Index for the Characterization of Extra Virgin Olive Oils

A new method for direct measurement of the oleocanthal and oleacein levels in olive oil by quantitative (1)H NMR was developed. The method was applied to the study of 175 monovarietal commercial Greek and California olive oil samples. The main findings were as follows: (1) There was a significant variation concerning the concentrations of oleocanthal and oleacein among the studied samples. Their concentrations ranged from nondetectable to 355 mg/kg and their sum (index D1) from 0 to 501 mg/kg. (2) There are olive varieties that independent of geographic origin and harvest time produce oil that contains both compounds in low levels. (3) There is a positive correlation of a high level of oleocanthal and oleacein in olive oils with the early time of harvest. Although there is a need for more extensive study, a new index for the characterization of extra virgin olive oils, which is a combination of D1 = oleocanthal + oleacein level and D2 = oleocanthal/oleacein ratio, seems to be very useful.

SENSORY CHARACTERIZATION OF CALIFORNIA'S OLIVE OILS

California olive oil industry is growing very rapidly with plantings of 1000 to 1500 hectares annually over the last three years. In 2007, there were an estimated 5550 ha with the production of premium quality olive oil predicted to triple by 2011. Very little historical information is available about olive oil production in California. Since premium oils rely primarily on sensory characteristics to determine price and popularity, a long term program was started to evaluate and characterize flavors of some of the world’s most popular cultivars grown in different regions of California. In 1996, fifteen cultivars from the same nursery source were planted in five different climatic zones in northern California. Over the last three years, fruit from each cultivar was harvested at approximately the same maturity index and made into oil using the Abencor system. Evaluation of the oils was conducted by trained tasters of the University of California Taste Panel. A 15-point profile sheet and data base were developed and used to rate oils by their specific flavor intensities and characteristics such as bitterness, pungency, aroma, complexity, and balance. Fruitiness undertone flavor characteristics such as nutty, buttery, floral, tropical, grassy, herbaceous, mint, eucalyptus, and spice were also noted in three different intensity levels (slight, moderate, or strong). Another six-seven growing seasons will be needed to sufficiently classify the cultivars with statistical reliability due to extensive variability from yearly climatic changes, alternate bearing, and fruit maturity influences. A general trend, however, has been that oils made from olives grown in cooler climates have higher flavor intensities. This evaluation process for olive oils has the potential to help farmers select cultivars, determine harvest dates, and blend oils to produce specific oil styles and flavors specific to targeted consumer groups.

UC Cooperative Extension sensory analysis panel enhances the quality of California olive oil

California's olive oil industry has evolved from primarily a salvage operation of the table olive industry to a producer of world-class, premium, extra-virgin olive oil. In 1997, UC Cooperative Extension started the first California olive oil taste panel, which was officially recognized by the International Olive Council in 2001. Specific protocols were used to screen potential panelists and train them to identify defects and positive characteristics, identical to 43 other world taste panels. The UCCE panel helped the California Olive Oil Council develop a seal certification program using sensory analysis. Certification provides consumers with assurance that labeled oils are free of defects and warrant the “extra virgin” grade. Sensory evaluation using a unique UCCE profile sheet provides complete and detailed information about specific positive flavor characteristics of olive cultivars grown in California. The UCCE sensory panel has also contributed to a better understanding of the qualities of California olive oil and advancement of the industry by participating in research on pest management, cultural practices and processing.

Characterization and Pathogenicity ofBotryosphaeriaceaeSpecies Collected from Olive and Other Hosts in Spain and California

Species in the family Botryosphaeriaceae are common pathogens causing fruit rot and dieback of many woody plants. In this study, 150 Botryosphaeriaceae isolates were collected from olive and other hosts in Spain and California. Representative isolates of each type were characterized based on morphological features and comparisons of DNA sequence data of three regions: internal transcribed spacer 5.8S, β-tubulin, and elongation factor. Three main species were identified as Neofusicoccum mediterraneum, causing dieback of branches of olive and pistachio; Diplodia seriata, causing decay of ripe fruit and dieback of olive branches; and Botryosphaeria dothidea, causing dalmatian disease on unripe olive fruit in Spain. Moreover, the sexual stage of this last species was also found attacking olive branches in California. In pathogenicity tests using unripe fruit and branches of olive, D. seriata isolates were the least aggressive on the fruit and branches while N. mediterraneum isolates were the most aggressive on both tissues. Isolates of B. dothidea which cause dalmatian disease on fruit were not pathogenic on branches and only weakly aggressive on fruit. These results, together with the close association between the presence of dalmatian disease symptoms and the wound created by the olive fly (Bactrocera oleae), suggest that the fly is essential for the initiation of the disease on fruit. Isolates recovered from dalmatian disease symptoms had an optimum of 26°C for mycelial growth and 30°C for conidial germination, suggesting that the pathogen is well adapted to high summer temperatures. In contrast, the range of water activity in the medium for growth of dalmatian isolates was 0.93 to 1 MPa, which was similar to that for the majority of fungi. This study resolved long-standing questions of identity and pathogenicity of species within the family Botryosphaeriaceae attacking olive trees in Spain and California.

Psyttalia ponerophaga (Hymenoptera: Braconidae) as a potential biological control agent of olive fruit fly Bactrocera oleae (Diptera: Tephritidae) in California

The olive fruit fly, Bactrocera oleae (Rossi), is a newly invasive, significant threat to California's olive industry. As part of a classical biological control programme, Psyttalia ponerophaga (Silvestri) was imported to California from Pakistan and evaluated in quarantine. Biological parameters that would improve rearing and field-release protocols and permit comparisons to other olive fruit fly biological control agents were measured. Potential barriers to the successful establishment of P. ponerophaga, including the geographic origins of parasitoid and pest populations and constraints imposed by fruit size, were also evaluated as part of this investigation. Under insectary conditions, all larval stages except neonates were acceptable hosts. Provided a choice of host ages, the parasitoids' host-searching and oviposition preferences were a positive function of host age, with most offspring reared from hosts attacked as third instars. Immature developmental time was a negative function of tested temperatures, ranging from 25.5 to 12.4 days at 22 and 30 degrees C, respectively. Evaluation of adult longevity, at constant temperatures ranging from 15 to 34 degrees C, showed that P. ponerophaga had a broad tolerance of temperature, living from 3 to 34 days at 34 and 15 degrees C, respectively. Lifetime fecundity was 18.7 +/- 2.8 adult offspring per female, with most eggs deposited within 12 days after adult eclosion. Olive size affected parasitoid performance, with lower parasitism levels on hosts feeding in larger olives. The implications of these findings are discussed with respect to field manipulation and selection of parasitoid species for olive fruit fly biological control in California and worldwide.

Diachasmimorpha longicaudata and D. kraussii (Hymenoptera: Braconidae), potential parasitoids of the olive fruit fly

The olive fruit fly, Bactrocera oleae (Tephritidae), is a significant threat to California's olive industry. As part of a classical biological control program started in 2002, the parasitoids Diachasmimorpha kraussii and D. longicaudata (Hymenoptera: Braconidae) were imported to California from laboratory colonies in Hawaii. Studies on their biology and behavior as parasitoids of the olive fruit fly were conducted in quarantine. Both species tend to oviposit into 2nd and young 3rd instars, with the offspring completing development in the flies’ puparia. Most eggs are deposited in the first two weeks of adult life. Observed lifetime fecundity was low, possibly as a consequence of the relatively poor quality of the harvested olives used as a host substrate. Both pre-imaginal development and adult longevity were limited at constant temperatures above 30°C, which may indicate that these species will have difficulty establishing in the warmest regions of California.

The panmixia paradigm of eastern Pacific olive ridley turtles revised: consequences for their conservation and evolutionary biology

Previous studies of the olive ridley Lepidochelys olivacea population structure in the tropical eastern Pacific have indicated the existence of a single panmictic population ranging from Costa Rica to Mexico. This information has been used to design specific management measures to conserve primary nesting beaches in Mexico. However, little is known about olive ridleys in the Baja California Peninsula, their northernmost reproductive limit, where recent observations have shown differences in nesting female behaviour and size of hatchlings relative to other continental rookeries. We used mtDNA control region sequences from 137 turtles from five continental and four peninsular nesting sites to determine whether such differences correspond to a genetic distinction of Baja California olive ridleys or to phenotypic plasticity associated with the extreme environmental nesting conditions of this region. We found that genetic diversity in peninsular turtles was significantly lower than in continental nesting colonies. Analysis of molecular variance revealed a significant population structure (Phi ST = 0.048, P = 0.006) with the inclusion of peninsular samples. Our results: (i) suggest that the observed phenotypic variation may be associated with genetic differentiation and reproductive isolation; (ii) support the recent colonization of the eastern Pacific by Lepidochelys; (iii) reveal genetic signatures of historical expansion and colonization events; and (iv) significantly challenge the notion of a single genetic and conservation unit of olive ridleys in the eastern Pacific. We conclude that conservation measures for olive ridleys in Mexico should be revised to grant peninsular beaches special attention.

The Olive in California: History of an Immigrant Tree

The Olive in California: History of an Immigrant Tree