From Plant Resources of South-East Asia No 2: Edible fruits and nuts, PROSEA Foundation
by N. Moutier and H. A. M. van der Vossen
Taxon
Olea europaea L.
Protologue
Sp. pl.: 8 (1753).
Family
OLEACEAE
Chromosome Numbers
2n = 46
Vernacular Names
Olive (En). Olivier (Fr). Indonesia: zaitun. Malaysia: zeitun. Philippines: oliva.
Origin and Geographic Distribution
The
olive is a characteristic fruit tree of the Mediterranean. Wild olive
(oleaster) is a typical component of the Mediterranean shrub vegetation
and the most likely progenitor of the cultivated olive trees. First
domestication is associated with early civilizations in the eastern
Mediterranean. Archaeological evidence of olive cultivation dates back
to the fourth millennium BC. The Phoenicians and Greeks in particular
contributed to the expansion of olive cultivation around the
Mediterranean Sea during the last millennium BC. In the Roman empire of
the 2nd Century AD, olive oil became one of the most economically
important commodities. Eastwards, olive cultivation spread up to
north-western India and the Caucasus. Olive cultivation was introduced
to the new world (Peru, Chile, Argentina, Mexico and United States
(California)) in the 16—18th Centuries by the Spanish, to Australia and
South Africa by Italian and Greek immigrants and to Japan and China
from France in the 19th Century. Nevertheless, about 97% of the world=s
800 million olive trees are still grown in the Mediterranean region.
Uses
The main product of the olive
tree is the edible oil extracted from the fruit's mesocarp and commonly
used as a cooking and salad oil and in the preservation of various
foods. It is much appreciated for its specific flavour and supposedly
beneficial effects on health due to the high concentration of
monounsaturated fatty acids and polyphenolic anti-oxidants. Lower grade
olive oils are used in the manufacturing of soap, cosmetics and
lubricants. Traditionally, olive oil also has various pharmaceutical
applications and has served as lamp oil.
Fruits are processed
into green and black table olives (whole, sliced, minced or paste). The
presscake is not a very suitable livestock feed, but can be used as
fuel or fertilizer. Other useful products from the olive tree include
the leaves as cattle feed, valuable timber from the stem, and firewood
from the branches. Olive trees are planted for ornamental purposes, as
firebreaks and to control soil erosion.
Production and International Trade
Average
world production of olive oil during the period 1995—2000 was 2.3
million t/year, almost all from the Mediterranean region. The biennial
bearing habit of the olive tree and variable weather conditions cause
considerable fluctuations in annual world production (1.6—2.8 million
t). The total area planted with olive trees is estimated at 9.1 million
ha in 21 countries. The principal olive oil producing countries are:
Spain (32%), Italy (21%), Greece (17%), Tunisia (8%), Syria (4%),
Turkey (4%), Morocco (3%) and Algeria (1%), which together account for
90% of the world supply. About 400 000 t per year reach the
international vegetable oil market; the European Union and United
States are the main importers of olive oil.
The 1.1 million t of
table olives produced annually represent about 8% of total olive fruit
yields. Spain is the largest producer of table olives (25%) followed by
the United States (14%), Turkey, Morocco, Syria, Greece and Italy (6—9%
each).
Properties
Mature
olive fruits consist of mesocarp (pulp) 70—90%, endocarp (stone) 9—29%
and seed 1—3%. Per 100 g fresh edible portion, the mesocarp contains:
water 60—70 g, oil 15—30 g, carbohydrates 3—6 g, crude protein 1—2 g,
cellulose 1—4 g, phenolic compounds 1—3 g, ash and other substances 1—3
g. The fatty acid composition of the oil is: palmitic acid 7.5—20%,
palmitoleic acid 0.3—3.5%, stearic acid 0.5—5%, oleic acid 55—83%,
linoleic acid 3.5—20%, linolenic acid 0—1.5%, arachidic acid 0.1—0.6%
and traces of gadoleic, behenic and lignoceric acids. The anti-oxidant
effect of the phenolic compounds (50—400 ppm) and the high oleic
content combine to give an oil of exceptional stability even during
deep frying. Olive oil is classified into two main quality classes:
cold-pressed or virgin oil and refined olive oil. Virgin olive oil is
one of the few vegetable oils that is traded and consumed without any
refinement and contains its full complement of secondary compounds.
Mainly oleuropein but also other phenolic compounds are responsible for
the intense bitterness of olive fruits, as well as for fruit blackening
and inhibition of microorganisms during processing. The bitterness in
table olives is largely removed in the early stages of processing. The
weight of a fresh fruit is 1—12 g.
Description
Evergreen
tree, up to 10—(15) m tall, with broad multibranched crown, trunk
thick, up to 1—2 m in diameter, often gnarled, or densely branched
shrub, up to 2(—5) m tall. Root system extensive with main roots
thickened due to fasciation, up to 6 m deep in porous soils and
spreading laterally with dense mat of feeder roots; protuberances
(spheroblasts) at the base of trunk with additional lateral roots.
Twigs grey, subterete and thornless in cultivars, 4-angled and thorny
in wild forms. Leaves opposite, simple, entire, coriaceous, subsessile;
blade elliptical to lanceolate, 1—8 cm x 0.5—2.5 cm, mucronate at apex,
dark grey-green and glabrous above, densely silvery lepidote beneath.
Inflorescence an axillary panicle, shorter than the leaves, 3—5 cm long
with 10—40 bisexual, white, fragrant flowers 3—4 mm long; pedicel
short; calyx cup-shaped with 4 teeth, persisting in fruit; corolla with
short tube and 4 valvate lobes; stamens 2, filaments short, anthers
large; pistil with superior, 2-loculed ovary, a short style and a
2-lobed stigma. Fruit a subglobose to ellipsoid drupe, 0.5—4 cm x
0.5—2.5 cm, bright green, turning purple-black, brown-green or
ivory-white at maturity; mesocarp rich in oil; endocarp stony, usually
containing 1 seed. Seed ellipsoid, 9—11 mm long with straight embryo
and copious endosperm. Seedling with epigeal germination.
Growth and Development
Practically
all olive trees in the world are grown from clonal cultivars. Seeds
germinate within 25—50 days after sowing, but seed viability of
cultivated olives is generally low. Olive seedlings have a distinct
juvenile phase lasting 4—9 years and characterized by strong vegetative
growth and profuse branching. Plants raised from cuttings have a more
adult growth habit with monopodial branching and may start flowering
within 3—7 years after field planting. The life of leaves is 2—3 years.
Flowering occurs annually in spring on branch segments formed during
the previous season, with 50—80% of the leaf axils developing
inflorescences. Wind pollination and cross-fertilization are the rule
due to self-incompatibility. Even under optimum conditions of
pollination and initial fruit set, generally only 1—5% of the flowers
will develop into mature fruits due to severe early (up to 50%) and
late physiological fruit abscission, water stress, diseases and pests.
In a year of profuse flowering, such low fruit set still represents a
large crop. Olive is a strongly biennial bearer, because a heavy fruit
load in one year inhibits adequate shoot extension necessary for the
following year=s bearing wood and vice versa. Olive fruit development
takes 6.5—7 months from anthesis to harvesting, the last 20—40 days
being essential for oil formation in the mesocarp.
The
commercial life span of an olive tree is about 50 years, but individual
trees can become very old (hundreds of years). Very often, old trees
are hollow, usually because during its history, fungus diseased wood
has been cut away repeatedly. Such old, gnarled trees are often also
twisted and slanting, giving the tree a peculiar appearance: abundant,
fresh, lively, young, green sprouts on an old, grey, twisted, gnarled
and slanting, hollow cylinder.
Other Botanical Information
The Olea europaea
taxonomy is confusing and many names and classifications exist.
Usually, 2 groups are distinguished: cultivated and wild, and a
selection of scientific names encountered for each group is listed:
— the cultivated olive: Olea europaea L. var. europaea, Olea europaea L. subsp. europaea, Olea gallica Miller, Olea hispanica Miller, Olea lancifolia Moench, Olea sativa Gaterau, Olea europaea L. var. sativa Lehr., Olea europaea L. var. sativaLoud., Olea europaea L. subsp. sativa Arcang.
— the wild olive: Olea europaea L. var. sylvestris (Miller) Lehr., Olea sylvestris Miller, Olea europaea L. subsp. sylvestris (Miller) Rouy, Olea europaea L. subsp. sylvestris (Miller) Hegi, Olea europaea L. var. sylvestris Brot., Olea oleaster Hoffmannsegg & Link, Olea europaea L. subsp. oleaster (Hoffmannsegg & Link) Negodi.
Instead
of classifying the cultivated olive into a system developed for wild
plants, it is better to distinguish cultivars and cultivar groups. More
than 2500 cultivars are known, but an overall cultivar classification
system has not yet been developed. According to their use, three groups
of cultivars can be distinguished:
— Cultivars for oil extraction,
e.g. 'Picual', 'Arbequina' and 'Blanqueta' in Spain; 'Frantoio' and
'Leccino' in Italy and 'Koroneiki' in Greece.
— Cultivars for fruit
consumption, e.g. 'Gordal Sevillana' and 'Manzanilla de Sevilla' in
Spain, 'Conservolea', 'Kalamata' and 'Chaldiki' in Greece, 'Picholine
du Languedoc' in France, 'Manzanillo' and 'Mission' in the United
States and 'Oliva di Spagna' and 'Oliva di Cerignola' in Italy.
—
Dual-purpose cultivars (for oil extraction and fruit consumption), e.g.
'Hojiblanca', 'Manzanilla Cacereña' and 'Aloreña' in Spain, 'Tanche' in
France, 'Picholine marocaine' in Morocco, 'Dan' in Syria and 'Arauco'
in Argentina.
It is generally believed that the cultivated olive originates from the wild form of Olea europaea
(often called 'oleaster') by selection of high oil yielding genotypes
and their vegetative propagation. Oleaster is distributed similarly to
the cultivated olive in the Mediterranean. It can be distinguished
by its obovate leaves (shorter than 4 cm), its thorny, quadrangular
lower twigs and its small fruits (up to 1.5 cm long). Oleaster fruits
have always been used for their edible oil. Sometimes, it is difficult
to decide to which group a plant belongs: in disturbed habitats (e.g.
near the edge of olive plantations), intermediate forms exist because
the two are interfertile. Many cultivars are genetically heterozygous
and they have often been grafted on wild oleaster stock.
Olea L. comprises about 35 species but in the Mediterranean only Olea europaea occurs. Several non-Mediterranean wild Oleaspecies, however, are closely related to and sometimes interfertile with Olea europaea. Some examples are: Olea chrysophylla Lamk (synonyms: Olea cuspidita Wall ex G. Don, Olea africana Miller, Olea verrucosa Link) occurring in southern Iran, southern Arabia and eastern Africa; Olea ferruginea Royle, occurring in South Asia; Olea laperrini Battand. & Trab., occurring in the mountains of the Sahara; and Olea cerasiformis Webb & Berth., occurring in the Canary Islands and Madeira. These taxa are so closely related to Olea europaea that they have also been classified as its subspecies (subsp. cuspidata (Wall. ex G. Don) Cif. and subsp. cerasiformis
(Webb & Berth.) Kunkel & Sunding). Their geographic isolation
from the location of early domestication of the olive makes them
unlikely progenitors, but they could become useful genetic resources
for the improvement of the cultivated olive, e.g. for disease and pest
resistance and adaptation to new ecosystems.
Ecology
The
olive tree is well adapted to the seasonal and relatively dry climate
of the Mediterranean region. Worldwide cultivation is concentrated
between 30—45° latitudes in the northern and southern hemispheres
(excluding the tropics), from sea level to 900 m altitude on
south-facing slopes (higher than 1200 m in Argentina). Frost in spring
can damage young shoots and flowers, and the ripening fruits in late
autumn. Olive trees are fairly frost-hardy during winter, tolerating
—8°C to —12°C. For flower initiation, most olive cultivars require a
vernalization period of 6—11 weeks below 9°C which ends 40—60 days
before anthesis. Optimum temperatures for shoot growth and flowering
are 18—22°C. Temperatures above 30°C in spring can damage flowers, but
the tree can withstand much higher temperatures in summer. The
xerophytic physiology of olive trees makes them highly tolerant of long
period of water stress, but for economic yields, low and irregular
rainfall (less than 300 mm) should be supplemented by irrigation during
critical growth stages to 500—800 mm per year.
Soils should be
light-textured (less than 20% clay), well-drained and have a depth of
at least 1.5 m. Olives can do well on very poor soils, except when
these are waterlogged, saline or too alkaline (higher than pH 8.5).
Propagation and planting
The
main method of propagation of olive is based on rooting of
semi-hardwood cuttings prepared from one-year old branches (10—12 cm
long with 4—5 nodes and two pairs of leaves). Propagation by seed is
possible but gives rather variable seedlings because of cross
fertilization. It is mostly used for breeding purposes. In vitro
micro-propagation of olive explants has not yet passed the experimental
stage, partly because of large variation in rates of success between
different cultivars. Somatic embryogenesis is very difficult to achieve
from adult tissues and cannot be used for propagation purposes.
Traditional methods of clonal propagation are: large hardwood cuttings,
grafting on seedlings or mature trees, grafting on wild olive trees and
rooting of fragments of protuberances with a shoot attached.
Protuberances can also be used for in situ rejuvenation of very old and
decaying olive trees.
Plants from rooted cuttings are raised in
beds or polythene bags in nurseries for 1.5—2 years prior to planting
in the field in spring. They are planted in large holes (40 cm x 40 cm
x 60 cm) which are later refilled with topsoil, organic compost and
fertilizers, especially P and K. Plant densities traditionally vary
from 40—60 trees/ha in very dry areas to 300—400 trees/ha under optimum
soil conditions and water availability (more than 600 mm) and using
cultivars with more compact and erect growth habit. Field experiments
with high density olive orchards (up to 2000 trees/ha planted in
hedges) are in progress in Spain and France. The majority of olive
orchards in the Mediterranean region have traditional densities of
100—250 trees/ha. Planting along contour lines or in terraces is
necessary in sloping terrain to prevent soil erosion. Leguminous and
cereal crops have been planted as intercrops in olive groves.
Husbandry
The
olive tree requires pruning to shape it into the desired main frame and
crown, to maintain a proper balance between vegetative growth and fruit
production and so reduce biennial bearing and to rejuvenate senescent
trees. There is a long tradition of manual pruning methods and some are
region specific. Mechanized maintenance pruning is done in modern olive
orchards, but requires adaptation of tree shape and careful management
to prevent excessive branch damage and subsequent disease problems.
Regular
fertilizer application is needed for sustained fruit production, but
type and rate vary with local climate, soil condition and agronomic
practice. Foliar analysis provides information on the nutrient status
of olive trees. Nutrients removed by 3 t of fruit amount to about 19 kg
N, 9 kg P2O5 and 25 Kg K2O. A general fertilizer recommendation would
be: annual applications of 0.8 kg N (in 2—3 split applications), 0.3 kg
P2O5 and 0.9 kg K2O per tree at medium planting density (150 trees/ha).
These correspond to 120 kg N, 45 kg P2O5 and 135 kg K2O per ha.
Occasional correction of calcium, magnesium and boron deficiencies may
also be needed. Triennial application of organic manure or compost (50
kg/tree) is recommended to improve soil texture and fertility. It can
also be done before planting.
Only 15% percent of areas planted
with olive trees worldwide are actually irrigated but this is steadily
increasing. Surface, sprinkler or drip irrigation are some of the
methods applied to supplement deficient rainfall in intensive olive
cultivation. Correctly timed and dosed irrigation is required to
produce economic responses in yield and fruit quality. Irrigation
combined with ground cover positively influence olive production and
soil conservation.
Diseases and Pests
Leaf spot or peacock spot caused by Spilocaea oleagina (Cycloconium oleaginum)
is the most common disease in olive cultivation. Methods of control
include preventive copper-based fungicide sprays and host resistance.
Copper sprays also have a tonic effect of promoting longer leaf
retention. Other diseases are sooty mould caused by secondary infection
of Alternaria, Capnodium and Cladosporium spp. following black scale infestation, Verticillium wilt caused by Verticillium dahliae and bacterial canker or olive knot caused by Pseudomonas syringaepv. savastanoi.
There
are numerous pests, which generally cause much more economic harm to
olive cultivation than diseases. The most damaging insect pests are the
olive fly (Bactrocera oleae) and olive moth or kernel borer (Prays oleae, synonym Prays oleellus) on fruits, black scale (Saissetia oleae) on branches, jasmin moth (Margaronia unionalis) on young shoots, bark beetles (Hylesinus oleiperda and Phloeotribus scarabaeoides) on branches and trunk, psyllids (Euphyllura olivina) sucking on flowers, mites (Aceria oleae) on leaves and fruits and thrips (Liothrips oleae)
on flowers and young leaves. Insect control in olive cultivation is
increasingly based on systems of integrated pest management including
monitoring, pheromone trapping, promoting or releasing natural enemies,
Bacillus thuringiensis-based insecticides and cultural measures such as pruning and irrigation.
Harvesting
Olives
for oil are harvested at full maturity in late autumn or early winter,
either mechanically or with the use of rakes, beating poles and
collecting nets. Table olives are harvested by hand; mature green
fruits in early autumn and black olives in late autumn. Manual fruit
picking (capacity about 80 kg/person per day) accounts for 50—60% of
field production costs. Machines developed to reduce harvesting costs
include trunk and branch shakers in combination with inverted umbrellas
or rolling canvas frames to catch the fruits. Self-propelled overhead
harvesting machines in olive orchards planted in hedge rows and the
application of chemicals (e.g. ethephon) to promote fruit abscission
shortly before harvesting are still in the testing stage.
Yield
World
average yield in 1999 was 1.7 t of olive fruits per ha. Fruit yield per
ha varies from less than 1—3 t in traditional olive groves to 4—10 t
under irrigation and optimum agronomic practices (e.g. in Italy at 280
trees per ha). In well-managed plantings under rainfed conditions,
fruit yield is 2—5 t/ha. There is always considerable year-to-year
variation in productivity. About 5—6 kg of fruits are needed to produce
1 kg oil. The world's average oil production in 1999 reached about 300
kg/ha.
Handling After Harvest
Oil
extraction should start within 3—4 days after fruit harvesting to avoid
a change in flavour and increase in free fatty acid content. The fruits
are washed, crushed and mashed into a paste, from which the oil is
cold-extracted by mechanical pressing. The 'margine', or mixture of
water and oil, is allowed to settle and the oil is separated by
decantation, centrifugation and filtration. Oil prepared exclusively by
this process, i.e. by physical means only and without any heating, is
called virgin olive oil. In the European Union, virgin olive oil is
graded into 4 classes based on many characteristics of which the most
important ones are free fatty acid content and organoleptic test score:
extra virgin oil, virgin oil, standard and 'lampante' virgin oil.
'Lampante' virgin oil and oil obtained by heating or solvent extraction
are either used industrially or have to be refined by neutralization,
bleaching and deodorization to produce refined olive oil. Further
solvent extraction may be done to produce an industrial grade oil from
the cake.
Preservation of table olives starts with soaking fruits in
an alkaline solution to reduce the bitterness before pickling in brine
(Spanish-style and Californian-style). The Greek-style preservation of
fully ripe, black olives involves pickling in brine without alkaline
pre-treatment.
Genetic Resources
The
numerous traditional olive cultivars (estimated at 2000) are gradually
disappearing because of abandonment of marginal groves and urbanization
or replacement by modern cultivars. Programmes to collect and preserve
this valuable olive germplasm are in progress with the support of the
International Olive Oil Council (COI) and the European Union. In
addition to the Olive World Collection at Cordoba (Spain) with 310
accessions, there are 73 collections of olive germplasm in 23 countries
and a project of a second world collection at Marrakech (Morocco).
Breeding
Olive
improvement has a long tradition of clonal selection. Breeding
programmes based on inter-varietal crosses followed by selection within
segregating seedling populations are of fairly recent date. The long
juvenile phase of olive seedlings has been an impediment to breeding,
but forcing methods and existing genetic variation in length of
juvenile phase have contributed to shorter breeding cycles. Main
criteria of selection in the olive are fruit yield, regular production,
cold tolerance, early first bearing, compact growth, oil content of the
fruit mesocarp, quality of the oil and resistance to diseases and
pests. Quality of olive oil is determined by standard physical and
chemical analyses and sensory assessment of taste and flavour. Host
resistance to Spilocaea oleagina has been reported in Israel and to Pseudomonas syringae pv. savastanoi in
Portugal. Progress is also being made with the application of molecular
biology in the olive, including molecular markers for cultivar
identification, the construction of a linkage genome map and marker
assisted selection. There are no crossing barriers for introgression of
desired characters from the oleaster olive and some related species.
Prospects
Increasing
interest in the olive as a source of high quality and healthy vegetable
oil may have a positive effect on world production, notwithstanding its
high production costs in relation to other vegetable oils. The olive
also contributes considerably to environmental protection (soils, flora
and fauna) in dry and hilly areas, particularly of the Mediterranean
region. There are prospects for olive cultivation in Australia, India,
China and possibly northern Thailand but possibilities in South-East
Asia are very limited.
Literature
Barranco,
D., Fernandez-Escobar, R. & Rallo, L. (Editors), 1998. El cultivo
del olivo [Olive growing]. Ediciones Mundi-Prensa, Madrid, Spain. 651
pp.
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Garrido
Fernandez, A., Fernandez Diez, M.J. & Adams, M.R., 1997. Table
olives, production and processing. Chapman & Hall, London, United
Kingdom. 495 pp.
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Katsoyannos,
P., 1992. Olive pests and their control in the Near East. FAO Plant
Production and Protection Paper 115. Food and Agriculture Organization,
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olive tree. Agricultural and production techniques in the
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I.T. & Voyiatzis, D.G. (Editors), 1999. Proceedings of the third
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September 1997. International Society for Horticultural Science. Acta
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