Agriculture Reference
In-Depth Information
cessive levels of ions by various eco-physiological mechanisms. Some halophytes
possess unique adaptations, such as salt glands or bladders that alleviate the delete-
rious effects of high ion concentrations. However, intrinsically cellular processes-
must make the major contribution to the capacity of plants for salt adaptation. At the
molecular level, the higher salt-adaptive plasticity of halophytes may be due to con-
stitutive expression of genes that encode salt-tolerance determinants (Casas et al.
1992
) or the better aptitude to regulate the expression of these genes in response to
salt. This hypothesis makes halophytes a source of exclusive genes or new genetic
mechanisms that could be applied in genetic manipulation of crops. Cultivation of
salt-tolerant crops, or halophytes, on saline soil has significant social and economi-
cal potential that needs to be further explored and developed (Debez et al.
2011
).
Among the halophytes extensively used in physiological and molecular bio-
logical investigations is the
Atriplex
genus. The genus
Atriplex
(Chenopodiaceae)
contains various species distinguishable by different morphology, biological
cycles and ecological adaptations (Le Houérou
1992
). Tolerance to salinity, drought,
heavy metals and temperature are important characteristics of species of
Atriplex
.
However, the value of certain
Atriplex
species has been recognized by their incor-
poration in the rangelands improvement programs in many salt-affected regions
throughout the world. In this contribution, we review the literature regarding the
ecological and agronomic importance of the plant genus
Atriplex
in arid and semi
arid regions.
Geographical Distribution of the Genus
Atriplex
Atriplex
species constitute the largest and most diversified genus of the family Che-
nopodiaceae (Kadereit et al.
2010
).
Atriplex
species (saltbushes) are dominant in
many arid and semi-arid regions of the world, particularly in habitats that combine
relatively high soil salinity with aridity (Ortíz-Dorda et al.
2005
). Over 400 spe-
cies of
Atriplex
have been found to be geographically distributed on all continents.
Atriplex
species are mainly found in the deserts and semi-deserts in North America,
South Australia, South Central Asia, West and South East America, and the Medi-
terranean basin.
A. nummularia
, and
A. halimus
are the most widely distributed
species of the genus
Atriplex
.
A. halimus
is a perennial native shrub of the Mediter-
ranean region (Ortíz-Dorda et al.
2005
). This species has two subspecies: the subsp.
halimus
, which is present on the northern shores of the Mediterranean basin and the
subsp.
schweinfurthii
(Boiss.) common on the southern shores of the Mediterranean
basin, North Africa and Near East.
A. nummularia
occurs naturally in the semi arid
and arid zone of southern and central Australia where it was divided in three subspe-
cies (subsp.
nummularia
; subsp.
Omissa
and subsp.
Spathulata
). Molecular genetic
and taxonomic evidence suggests that
Atriplex
was transported to Australia during
the late Miocene (Kadereit et al.
2010
).
A. nummularia
is proposed to have evolved
from a common octoploid ancestor
A. paludosa
ssp.
moquiniana
(Moq.) Parr-Smith
in the coastal semi-arid fringe of southwestern Australia. Sampson and Byrne
Search WWH ::
Custom Search