- Author: Elizabeth Fichtner
Recent advances in understanding the history of olive domestication
Elizabeth Fichtner, Farm Advisor, UCCE Tulare and Kings Counties
Olives are thought to have first been domesticated in the northeastern Levant, an area near the border of present-day Turkey and Syria. Map captured from Google Maps.
With the emergence of the California olive oil industry, the state has witnessed a dramatic diversification in the olive cultivars grown commercially. Our mainstay black ripe olive industry, dominated by the ‘Manzanillo' olive, is now combined with increasing acreage of Spanish, Greek, and Italian cultivars used to create high quality, extra virgin oil. The historic table olive industry of California still represents around 18,000 acres of olives in the state, while approximately 40,000 acres are currently devoted to oil production.
Although olive cultivation in California is relatively new (dating back to the historic Spanish Missions established by Franciscan priests), olives are of key importance in the history and culture of the Mediterranean basin. A recent publication by a group of European, American, and North African scientists has re-evaluated the location of the domestication of the olive, providing genetic evidence that domestication occurred in the northeastern Levant, close to the present-day border of Syria and Turkey.
To complete the study, researchers collected plant material from nearly 2000 trees, sampling both wild oleaster populations and domesticated cultivars of olive. World Olive Germplasm Banks in Córdoba (Spain) and Marrakech (Morocco) served as sources of the majority of cultivars included in the study. Researchers utilized the genetic sequences of plastids (ie. chloroplasts) to discern differences between cultivars and wild oleaster populations. Plastids are organelles (structures inside cells) that contain their own DNA. Since plastids are generally inherited from one parent (similar to mitochondria), their genetic sequences are more conserved then that of nuclear DNA, which is contributed by both parents. Since olive is a wind-pollinated crop, nuclear DNA may be disseminated over large distances.
The genetic analysis of wild populations indicates three distinct lineages of olive: the Near East (including Cyprus), the Agean area, and the Straight of Gibralter. These three wild populations are likely linked to refuge areas where populations persisted through historic glaciation events. Interestingly, the geographic distribution of these three populations also corresponds to the subdivisions of the olive fruit fly, suggesting that these regions offered shared refuge habitat for both the host and the pest. The wild oleaster population in the eastern Mediterranean was found to be more diverse than previously thought and ninety percent of the present-day cultivars analyzed in the study matched this group. Common olive cultivars grown in California, including, Sevillano, Arbosana, Arbequina, and Koroneiki, all belong to this group originating in the eastern Mediterranean.
As a result of this study, it is proposed that the initial domestication of olive took place in the northeastern Levant; subsequently, plant material was disseminated to the whole Levant and Cyprus before being spread to the western Mediterranean. After these initial domesticated trees spread throughout the Mediterranean basin, they likely underwent subsequent domestication events by crossing with wild oleasters, thus introducing genetic material from the other two ancient western Mediterranean lineages.
Such studies may appear purely academic; however, they can also address more timely questions and assist in characterizing cultivars. For example, a 2010 study in California made genotypic comparisons between historic olive plantings in Santa Barbara, CA and at Santa Cruz Island, CA. The study elucidated that the olives on Santa Cruz Island, planted in the late 19th century are different than other historic olive plantings in Santa Barbara, CA. Olives planted at the Santa Barbara Mission in the late 18th century are the ‘Mission' cultivar, whereas those on Santa Cruz Island (Figure 3) are generally ‘Redding Picholine.' Interestingly, the olives on Santa Cruz Island are thought to have been planted for oil production, but there are no historic reports of harvest or sale of a crop. Additionally, the Santa Cruz Island olives have become somewhat invasive on the island due to their propensity to establish from seed. As a result of genotypic analysis of these populations and the fact that ‘Picholine' makes an excellent rootstock due to its ease of propagation from seed, it is hypothesized that the ‘Picholine' variety was intended as a rootstock, but the grafts never took. Consequently, maturation of a ‘Picholine' orchard may have just been an accident, a mistake, or simply bad luck. The completion of this local population genetics study may have helped explain the unsolved mystery of the historically unharvested trees on Santa Cruz Island.
Find Santa Cruz Island.
Besnard, G., Khadari, B., Navascués, M., Fernández-Mazuecos, El Bakkali, A., Arrigo, N., Baali-Cherif, D., Brunini-Bronzini de Caraffa, V., Santoni, S., Vargas, P., Savolainen, V. 2013. The complex history of the olive tree: from Late Quaternary diversification of Mediterranean lineages to primary domestication in the northern Levant. Proc R Soc B. 280: 20122833.
Soleri, D., Koehmstedt, A., Aradhya, M.K., Polito, V., Pinney, K. 2010. Comparing the historic olive trees (Olea europaea L.) of Santa Cruz Island with contemporaneous trees in the Santa Barbara, CA area: a case study of diversity and structure in an introduced agricultural species conserved in situ. Genet Resour Crop Evol 57:973-984.
- Author: Ben Faber
It just came to my attention that there is a map of all the oil pipelines in the US. If you go to the bottom/left side and put in the state and county, it will be revealed. This is mainly for those growers who need to be aware of pipelines and tillage or any other work in the aerea of a pipeline.
- Author: Nastaran Tofangsazi and Beth Grafton-Cardwell, Department of Entomology, UC Riverside
With the detection of Huanglongbing (HLB) in California in 2012 and 22 additional cases reported during 2015 through June 2016 there is a major concern among citrus growers about the spread of this incurable bacterial disease. The vector of the disease, the Asian citrus psyllid (ACP), is a hardy insect with good dispersal capabilities and can be found in many southern California citrus groves today. With no direct cure for HLB at present, the only option for growers to combat the disease is to control the psyllid. This can prove difficult for conventional citrus growers with broad spectrum insecticides, but for organic citrus growers, which grow an estimated 7% of citrus in California, the task is even more difficult with the currently available options.
Entrust (spinosad) + oil, Pyganic (pyrethrin) + oil, and oil alone are currently the recommended and most widely used insecticide options for organic growers (UC IPM Guidelines for Citrus). While these insecticides are fairly effective in killing ACP if they make direct contact, the residual life of these pesticides is very short (days) compared to conventional insecticides (weeks to months). For example, in our petri dish studies, 10 fl oz/acre Entrust SC + 0.25% Omni supreme spray oil caused 89% mortality, 17 fl oz/acre Pyganic 5.0 EC + 0.25% Omni supreme spray oil caused 73% mortality and 0.25% Omni supreme spray oil caused 42% mortality when 1st-2nd ACP nymphs were exposed to treated leaves one day after application. Nymphal mortality continued to decline for the Entrust + oil treatment (69% mortality) and even more severely declined for Pyganic + oil (27% mortality) 3 days after treatment. In contrast, one-day-old residues of a conventional insecticide, the neonicotinoid 5.5 oz Actara (thiamethoxam), resulted in more than 95% mortality of nymphs and mortality remained high for more than a month.
Studies of grower orchard treatments confirmed laboratory studies that showed a short residual effect of organic treatments (Entrust + oil and oil alone) compared to conventional insecticides (Actara). We monitored changes in population densities of ACP (adults by tap, nymphs and eggs by flush examinations) in the fall of 2015 before and after a grower sprayed separate orchards with one of three insecticides; 1) 1.25% 440 Supreme Spray Oil by ground application (400 gpa), or 2) 9 fl oz Entrust SC + 1% oil by air (50 gpa), or 3) 5.5 oz Actara by air (50 gpa). The oil treatment had little effect on the adult population, but significantly reduced psyllid nymph densities for 17-24 days. Entrust was completely ineffective in controlling psyllid nymphs, but suppressed adult and egg populations for about 14 days. Actara, a conventional insecticide, was the most effective treatment in the study and provided more than 5 weeks of both adult and nymph control. Because of the short residual effect of organic insecticides in citrus, repeat treatments are needed at a frequency of about every 2 weeks for ACP control.
Tamarixia radiata wasps released for biological control of ACP provide 20% to 88% parasitism depending on geographical location and time of year. If there were no disease to be concerned about, this level of parasitism by Tamarixia would be sufficient to protect citrus from the feeding damage of the psyllid. However, the disease spreads rapidly with just a few psyllids and so a greater level of control is needed. Generalist predators, such as lady beetles, lacewings and assassin bugs, also assist with control. Argentine ants can severely disrupt this parasitism by protecting psyllids from natural enemies. Unhappily, Entrust + oil, thought of as a very selective insecticide combination, was found to be highly toxic to adult Tamarixia wasps exposed to 3 day old residues. Thus, the organic insecticide that is the best for controlling the psyllid pest is not compatible with the parasitoid natural enemy, limiting our ability to use integrated strategies to control the psyllid.
At present, it is not mandatory, but is strongly recommended, that all southern California citrus growers treat their orchards in an area wide manner. The area wide program consists of coordinated treatments twice a year (winter and fall), and additional treatments in between. Due to the short residual nature of organic insecticides, organic applications should be applied twice within 10-14 days of each other for every single conventional insecticide application. This is especially important for younger groves as ACP nymphs thrive in new flush. Organic growers have a tough decision to make between treating frequently for ACP and the high cost associated with those treatments or transitioning into conventional management in order to more effectively control ACP. Additional solutions are needed for organic citrus.
UC IPM Guidelines for Citrus: Asian Citrus Psyllid. http://ipm.ucanr.edu/PMG/r107304411.html