Agriculture Reference
In-Depth Information
Geographic Distribution and Production
Citrus are grown in most of the tropical and subtropical regions of the world between
the latitudes 40 °N to 40 °S. However, the large-scale, commercial plantations of
citrus have developed almost exclusively in subtropical regions where temperatures
are moderated by sea winds. These occur in two fringes around the world that ex-
tend roughly between 20 ° and 40 °N and S of the equator.
Currently, citrus is the main fruit tree crop in the world. By 2010 world citrus
fruit production was about 104 million t, with a crop area exceeding 7.1 × 10
6
ha.
Brazil (20.2 × 10
6
t) and China (16.2 × 10
6
t) continue to be the main producing
countries, followed by India (8.6 × 10
6
t), USA (7.5 × 10
6
t), México (5.9 × 10
6
t),
Spain (5.0 × 10
6
t) and others (FAO 2012).
Taxonomy
Citrus
species and related genera belong to the order Geraniales, suborder Gera-
niineae, and family Rutaceae. The family is subdivided into six subfamilies; the
subfamily Aurantioideae includes true citrus and related genera. See the review by
Swingle and Reece (
1967
) for further information. Within the Aurantioideae there
are many tribes, subtribes, genera and species. The tribe Citreae, subtribe Citrinae,
contains six genera including
Citrus
,
Poncirus
,
Eremocitrus
,
Microcitrus
,
Fortunel-
la
and
Clymenia
. Primitive citrus relatives and the true citrus group are included in
these genera, but only
Fortunella
,
Poncirus
and, above all,
Citrus
, have commercial
interest.
The genus
Fortunella
(kumquat) includes four species of small trees, leaves and
fruits. Leaves are unifoliate, flowers are borne singly or in clusters in the leaf axils,
and fruits ranging in shape from ovate to round.
The genus
Poncirus
has two species,
P. trifoliate
and
P. polyandra
. The trees
are small in size with trifoliate, deciduous leaves. Bud scales are pronounced and
produce long thorns in the leaf axils. Flowers are globular and fruits are small and
pubescent, and have a very bitter taste.
Poncirus
trees, and its intergeneric hybrids,
are used as rootstocks.
The genus
Citrus
consists of several species of evergreen trees ranging in size
from moderate to large. Branches are angular with numerous thorns when young
and cylindrical with less prominent thorns when mature. Leaves are unifoliate, and
vary in size depending on the species. Flowers are borne single or in clusters. Flow-
ers generally have 5 sepals, 5 petals, 20-40 stamens and a single ovary with 8-12
fused carpels (segments) containing 4-8 ovules each. The style is long and has one
stigma. The fruit varies in shape and size depending on the species and varieties and
has a peel containing numerous oil glands and two tissues. The external part of the
peel is called the flavedo; the internal one is called the albedo. Flavedo is a leathery
tissue that varies in colour from orange and reddish orange (oranges) to deep orange
