Publication
from Agroforestree Database: a tree reference and selection guide
version 4.0
by C. Orwa, A. Mutua, R. Kindt, R. Jamnadass and S. Anthony
Ceratonia siliqua
Local Names: Arabic
(al-kharoubah, kharrub), Catalan (garrover, garrofer), English (St.
John’s bread, locust bean, carob tree, carob bean), French (caroubier),
German (Karubenßaum, Johannisbrotßaum), Greek (charaoupi), Hindi
(kharnub), Italian (carrubo), Malay (gelenggang); Mandarin
(chiao-tou-shu); Portuguese (alfarrobeira); Spanish (garrover,
algarrobo, garrofero); Thai (chum het tai); Trade name (carob
tree, locust bean, chocar); Turkish (charnup)
Family: Fabaceae - Caesalpinioideae
Botanic
Description
Ceratonia siliqua is an evergreen shrub or tree up to 10 m high, crown broad semi-spherical, thick trunk, brown rough bark and sturdy branches.
Leaves
10-20 cm long, alternate, pinnate, with or without a terminal leaflet.
Leaflets 3-7 cm long, ovate to elliptic, 4-10 normally opposite pairs,
coriaceous, dark green and shiny above, pale green beneath finely
veined with margins slightly ondulate, tiny stipules.
Flowers
green-tinted red, small, numerous, 6-12 mm long, spirally arranged
along the inflorescence axis in catkin-like racemes borne on spurs from
old wood and even on the trunk (cauliflory). Pentamerous symmetry with
calyx but not corolla placed on a short pedicel. Calyx disc-shaped,
reddish-green, bears nectaries. Females consist of a pistil (6-8.5 mm)
on a disk and rudimentary stamens, 5 hairy sepals. Males consist of a
nectarial disk, 5 stamens with delicate filaments hairy sepals. In the
centre of the disk there is a rudimentary pistil. Hermaphrodite flowers
a combination; containing a pistil and a complement of 5 stamens.
The
fruit indehiscent pod, elongated, compressed, straight or curved,
thickened at the sutures, 10-30 x 1.5-3.5 cm, about 1 cm thick with
blunt or subacute apex. Pods brown, wrinkled surface, leathery when
ripe. Seeds occur in the pod transversally, separated by mesocarp; very
hard, numerous, compressed ovate-oblong, 8-10 x 7-8 mm, 3-5 mm thick;
testa is hard, smooth, glossy brown, hilium minute.
The
scientific name of the carob tree derives from the Greek ‘keras’, horn,
and Latin ‘siliqua’, alluding to the hardness and shape of the pod. The
common name originates from the Hebrew-'kharuv’, from which other
vernacular names are derived.
Biology
C. siliqua
is a dioecious tree with some hermaphroditic forms; male, female and
hermaphroditic flowers are generally borne on different trees.
Unisexual and bisexual flowers are rare in the same inflorescence. The
flowers are initially bisexual, but usually 1 sex is suppressed during
the development of functionally male or female flowers.
C. siliqua
is the only Mediterranean tree with the main flowering season in autumn
(September-November). However, the time and the length of the flowering
period depend on local climatic conditions, as with most fruit and nut
trees. Carob bean size is a highly variable character, influenced by
many environmental factors as well as level of pollination and fruit
set.
Pollen dispersal is by insects, mainly bees, flies, wasps
and night-flying moths. Flowers of all 3 types secrete nectar; the
volume of nectar and its sugar content are higher in female flowers
than in male. Male and hermaphroditic flowers emit a semen-like odour
that attracts insects.
Harvesting is the major cost in carob
production. Collecting operations depend on yield, size and shape of
pod, and orchard density
Ecology
A long-lived
evergreen and thermophilic tree thriving in habitats with mild
Mediterranean climates. It grows well in warm temperate and subtropical
areas, tolerates hot and humid coastal areas. It is a xerophytic
species, well adapted to the ecological conditions of the Mediterranean
region. C. siliqua, together with Olea europea var. sylvestris,
forms one of the most characteristic associations of the lowest
Mediterranean vegetation zone and is thus considered a climax community
(Olea-Ceratonion). Areas suitable for C. siliqua
should have a subtropical Mediterranean climate with cool, not cold,
winters, mild to warm springs, and warm to hot, dry summers.
Cannot
withstand waterlogging although the root system is usually deep. The
tree’s extensive root system penetrates the soil deeply; roots develop
under stressful conditions to explore deeper layers where water may be
available; it can thus survive long periods of drought. In addition the
leaves can maintain turgor under situations of drought, using different
strategies according to the season.
Sensitivity to frost is a
serious problem in this crop. The extent of frost damage depends on the
temperature within the orchard and the physiological state of the
trees. Noted for its drought resistance, the plant is especially
useful where irrigation is impractical or rainfall unreliable. However,
unless irrigated, the fruits are dry and shrivelled, having little
commercial value, and the yields are very low. Although
drought-resistant, C. siliqua
trees do not bear commercial crops unless they receive at least 500-550
mm/year, but 350 mm of annual rainfall is considered enough for fruit
set.
Biophysical
Limits
Altitude: 0-500 m, Mean annual temperature: -4 to 40 deg. C, Mean annual rainfall: 250-550 mm
Soil
type: Adaptable to a wide range of soils; poor sandy soils, rocky
hillsides, deep soils. Prefers sandy well-drained loams; calcareous
soils with high lime content also suitable. Appears to tolerate
salinity well.
Documented
Species Distribution
Native: Cyprus, Egypt, Israel, Jordan, Lebanon, Libyan Arab Jamahiriya, Saudi Arabia, Syrian Arab Republic, Tunisia, Turkey
Exotic: Algeria,
Argentina, Australia, Chile, Croatia, France, Greece, India, Indonesia,
Italy, Malta, Mexico, Morocco, Pakistan, Portugal, South Africa, Spain,
US, Venezuela, Yugoslavia (Former)
The
map above shows countries where the species has been planted. It does
neither suggest that the species can be planted in every ecological
zone within that country, nor that the species can not be planted in
other countries than those depicted. Since some tree species are
invasive, you need to follow biosafety procedures that apply to your
planting site.
Products
Food: Carob pulp is
high in total sugar content (48-56%). In addition, it contains about
18% cellulose and hemicellulose. Mineral composition consists of
potassium, calcium, magnesium, sodium, iron, copper, iron, manganese
and zinc.
In some countries, Egypt for example, carob syrup is a
popular drink, obtained from carob kibbles with water. Unicellular
organisms convert carob pulp into a high-protein feed; sugar solutions
extracted from carob pods are an excellent substrate for culturing
fungi such as Aspergillus niger and Fusarium monoliforme,
and the dried mycelium is a palatable and nutritious feed, containing
up to 38% crude protein by weight. The carob product most widely used,
especially in the food industry, is carob bean gum (CBG), or locust
bean gum (LBG). This gum comes from the seed endosperm and chemically
is a polysaccharide, a galactomnnan. 100 kg of seeds yield 20 kg on
average of pure dry gum.
The mucilaginous gum, known as
‘tragasol’, is used in a wide range of commercial products as a
thickener, stabilizer, binder and gelling or dispersal agent. The food
industry uses CBG for the production of a large number of different
commodities: ice cream, soups, sauces, cheese, fruit pies, canned
meats, confectionery, bakery products and pet foods. Technical
applications of CBG include cosmetics, pharmaceuticals, film emulsions,
paints, polishes, ceramics and adhesives.
Pulp extracted and
purified produces sugar and molasses. Powdered pulp is used as a food
ingredient and cacao substitute and for preparing dietary products.
Carob powder consists of 46% sugar, 7% protein and small amounts of
numerous minerals and vitamins and is thus quite nutritious. Carob
‘cocoa’ has an advantage over chocolate in that it has fewer calories
and neither caffeine nor theobromine. Ground seed embryo and endosperm
can be used for human consumption; the latter, containing CBG and
E-410, is a food additive and a dietary fibre.
Fodder: C. siliqua
pods provide fodder for ruminants and non-ruminants. Endosperm and
embryo of the seed can be ground and used for pet food. The fodder is
now being used in zero-grazing in Mediterranean countries.
Fuel: The wood produces a slow-burning charcoal and can also be used for firewood.
Timber: C. siliqua timber is hard and close-grained and has been used to make utensils.
Gum or resin: Currently, the main use of the seed is gum extraction.
Tannin or
dyestuff: Ripe carob pods contain large amounts of condensed tannins (16-20% of dry weight).
Alcohol: A high sugar content
and its relatively low cost have made carob pulp among the earliest
horticultural crops used for the production of industrial alcohol by
fermentation in several Mediterranean countries.
Medicine:
Tannins extracted from the pulp act as an anti-diarrhoetic. Ground pulp
and seed endosperm are used in the preparation of pharmaceutical
products.
Other products: Technical
applications of CBG (carob bean gum) include cosmetics,
pharmaceuticals, film emulsions, paints, polishes, ceramics and
adhesives.
Services
Shade or shelter: Widely planted as a shade tree, also recommended as a windbreak around orchards.
Reclamation: Since it requires little if any cultivation, tolerates poor soils and is long lived, C. siliqua is often recommended for reforestation of degraded coastal zones threatened by soil erosion and desertification.
Ornamental: A
popular ornamental in California, Australia and elsewhere; male trees
are preferred as they do not provide litter from pod fall. However, the
value of C. siliqua as a
drought-tolerant, air-pollution tolerant, low maintenance tree for
street landscape planting could be limited by its large size when
mature and its strong, invasive roots.
Intercropping: Frequently planted with species such as olive, grapevines or almond. Young C. siliqua
orchards are intercropped with early-bearing species such as peach,
almond or even vegetables; an annual perennial crop between the rows
may give early returns to the investment.
Pollution: Could help buffer noise from factories, roads and railways because of its dense foliage.
Tree
Management
Seedling
rootstocks, before or after budding, are usually planted from pots
directly into the orchard. Trees with well-developed roots should be
used for transplanting, and proper care during and after planting is
essential.
For dryland orchards on poor soils on the
Mediterranean coast, tree densities between 100 and 175 trees/ha are
recommended, that is, spacing from 9 x 9 m to 7 x 8 m. When C. siliqua
is to be planted in fertile soils, high-density planting and tree
thinning later may be considered. Little pruning is necessary due to
the tree’s specific growth and fruiting habits.
If male and
hermaphroditic trees are planted as pollinators they must be
interspersed around and within the orchard in a regular pattern. It is
important to use different types of male or hermaphroditic pollinators
to overlap with female cultivar bloom, as main cultivars often display
a long blooming season of 3-4 months. Since male trees have a shorter
flowering period than hermaphrodites, the latter usually show better
overlapping.
Germplasm Management
Orthodox
seed storage behaviour; viability can be maintained for 5 years in
air-dry storage at 5 deg. C without loss in viability. Although carob
seeds have remained viable for as long as 5 years stored at low
temperatures in sealed containers, it is advisable to use seeds from
the current season. Seeds are presumably viable after passing through
an animal’s digestive tract. There are about 500 seeds/kg.
Pests and
Diseases
C. siliqua
is normally free from severe insect and disease troubles and
traditionally is a crop that is not sprayed. In Spain, the most
damaging insect is the polyphagous larva of the leopard moth (Zeuzera pyrina),
which attacks the wood of trunk and branches, causing severe damage to
younger trees. Pods of many cultivars may become infested with the
small and polyphagous larva of the carob moth (Myelois ceratoniae) while maturing or before harvest is complete. In Cyprus, carob midge (Asphondylia
spp.) attacks on pods at an early stage have caused stunting. Black
aphids attack mainly the terminal shoots of young trees. The mildew
disease caused by Odium ceratoniae
attacks pods, leaves and twigs in different periods of the year. Other
pests that occasionally cause severe damage to the carob orchards are
small rodents like gophers (Pitymys spp.) and rats (Rattus
spp.). Gophers can severely damage the root system of young trees. Rats
can strip the bark not only of young shoots but also of older shoots
and even limbs; and by girdling a limb or branch can kill the plant.
Further
Reading
Anon. 1986. The useful plants of India. Publications & Information Directorate, CSIR, New Delhi, India.
Batlle I, Tous J. Carob tree, Ceratonia siliqua
L. Promoting the conservation and use of underutilized and neglected
crops. No. 17. Institute of Plant Genetics and Crop Plant Research,
Gatersleben/International Plant Genetic Resources Institute, Rome.
Esbenshade HW, Wilson G. 1986. Growing carobs in Australia. Goddard and Dobson Publishers. Victoria.
Hong TD, Linington S, Ellis RH. 1996. Seed storage behaviour: a compendium. Handbooks for Genebanks: No. 4. IPGRI.
Lanzara P. and Pizzetti M. 1978. Simon & Schuster's Guide to Trees. New York: Simon and Schuster.
National Academy of Sciences. 1979. Tropical legumes: resources for the future. National Academy Press. Washington D.C.
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