Salt stress and leguminous crops: Present status and prospects - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 25

likely to increase as human pressure places greater
demand on marginal land. Many Leguminosae species
are characteristic of open and disturbed places and are
thus well adapted to grow under poor conditions
( www.ildis.org ).
The yields and productivity of legume crops have
been reported to be low in developing countries over
the past few decades. Agricultural research and
development efforts in many of these countries have
focused mainly on improving cereal yields and pro-
duction to attain food security. However, reorientation
of the research spotlight on legumes will have impor-
tant impacts on nutritional security and soil fertility.
Recently observed rising prices reflect the escalating
demand for legumes worldwide due to increasing
incomes and population. The swelling demand for live-
stock feed, even in developing countries, is a noteworthy
systemic change in the demand structure. In addition,
the significant demand from the biodiesel industry for
soybean due to the current policy initiatives in Europe
and the USA, has also contributed to the upsurge in
demand and prices of substitute crops. These factors
mean that in the near future there will be substantive
shifts in the utilization patterns and price structure for
legumes (Gowda et al., 2009).
The Leguminosae family is usually divided into
three subfamilies: Papilionoideae, Caesalpinoideae and
Mimosoideae (Raven & Pothill, 1981; Doyle & Luckow,
2003). The Papilionoideae is the largest of the three
subfamilies, with about two-thirds of all the genera and
species of the family. It is also the most widespread,
extending further into temperate regions than the
other two subfamilies. The two major groups of culti-
vated species in the Papilionoideae are the tropical or
'phaseoloid' legumes ( Phaseolus , Vigna , Glycine and
Cajanus) and the temperate or 'galegoid' legumes
( Melilotus , Trifolium , Medicago , Pisum , Vicia , Lotus , Cicer ,
Lens and Lathyrus ) . Groundnut is somewhat distinct
from the phaseoloid and galegoid groups of grain
legumes (Upadhyaya et al., 2009). The United Nations
Food and Agriculture Organization (FAO, 1994) recog-
nizes 11 categories of annual leguminous crops or
pulses ( http://www.fao.org) . These are: dry beans, dry
broad beans, dry peas, chickpea, dry cowpea, pigeon
peas, lentils, Bambara beans, vetches, lupins and pulses
nes. Crops like soybean and groundnut (used mainly
for oil extraction) are excluded by the FAO from the list
of pulses (Table 2.1).

The Leguminosae (Fabaceae) plant family seems to be
particularly sensitive to salinity (Maas & Hoffman, 1977).
Salinity tolerance was placed into four categories:
• salt sensitive (80% of biomass production compared
to control at ~3 dS/m (equivalent to about 30 mM
NaCl);
• moderately sensitive (80% of biomass production at
~6 dS/m (~60 mM NaCl);
• moderately tolerant (80% biomass production at ~11
dS/m (~110 mM NaCl);
• tolerant (80% of biomass production at ~16 dS/m
(~160 mM NaCl).
Using these four categories defined by Maas and
Hoffman (1977), the majority of legumes are sensitive
or moderately sensitive. Legumes not only suffer
directly from salt stress like all plants, but also their
symbiotic associations show greater sensitivity to salinity
than either partner alone. Salinity impacts on various
phases of the initiation of symbiosis, nodule formation
and functionality (Maas & Hoffman, 1977; Bruning &
Rozema, 2013).
A comprehensive list of 1554 halophytes was compiled
by James Aronson in 1980. His HALOPH database of salt-
tolerant plants of the world was published in 1984 by the
Office of Arid Land Studies at the University of Arizona,
Tucson, Arizona. This database originally was compiled
according to the maximum salinity tolerated by the plant,
where this information was available, and expressed as
the ECe for a solution in which the plants were growing
together with its photosynthetic pathway where known
( http://www.sussex.ac.uk/affiliates/halophytes/index.
php ). Recently Bruning and Rozema (2013) focused on
the potential use of legumes in saline agriculture as crops
and for fodder, forage or other economically viable uses.
There are 46 legumes that are tolerant to salinity levels
ranging from 8 dS/m to seawater salinity in the eHA-
LOPH database. This includes annuals and perennials,
and legume species from tropical, subtropical and
temperate regions. However, most of the species are trees
and herbaceous perennials. Many legumes are sensitive
to salinity and as a group contain a relatively lower
proportion (0.2%) of tolerant species than the background
percentage (1%) of all land plants (Rozema & Flowers,
2008). Of four of the most commonly grown legumes in
agriculture, namely pea, chickpea, common bean and
soybean, soybean is the most salt tolerant (Delgado et al.,
1994). Manchanda and Garg (2008) reviewed the
responses of legumes to salinity stress with emphasis on