Legumes and breeding under abiotic stress: An overview - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 3

Generally, the mechanisms of drought tolerance
include (i) escape, (ii) avoidance, or (iii) resistance
(Ishitani et al., 2011; Toker & Mutlu, 2011; Impa et al.
2012; Rapparini & Peñuelas, 2014). There are several
screening and selection techniques for drought toler-
ance in food legumes; however, few techniques have
been successful under field conditions (Toker & Mutlu,
2011):
1 Line source sprinkler irrigation systems (Saxena et
al., 1993).
2 Root trait characteristics (root length, root density,
root biomass, root length density; Serraj et al., 2004)
and the 'root-box pin board' method (Singh &
Matsui, 2002).
3 Delayed sowing strategy (Singh et al., 1997).
4 Comparison of lines under non-stressed and stress
conditions by defined formula (Silim & Saxena,
1993; Toker & Cagirgan 1998).
5 Rain-out shelter tunnels (Abdelmula et al., 1999;
Amede et al., 1999; Link et al., 1999).
[Methods 1-5 can be useful for large-scale screening,
but are labour and time consuming (Toker & Mutlu,
2011).]
6 Delayed canopy wilting (DCW) in soybean (Charlson
et al., 2009).
7 Delayed leaf senescence (DLS) trait in cowpea (Hall
et al., 2002).
8 Leaf pubescence density (LPD) in soybean for
drought-prone environments (Du et al., 2009).
9 Recovery ability after wilting (RAW) in chickpea
(Toker et al., 2007b).
10 The use of carbon isotope discrimination (∆ 13 C) in
screening. This is described for some food legumes
(Stoddard et al., 2006; Khan et al. 2010), but it incurs
high costs per sample (Toker & Mutlu, 2011).

oxidative stress, alteration of metabolic processes, mem-
brane disorganization, reduction of cell division and
expansion, and genotoxicity (Hasegawa et al., 2000,
Munns, 2002; Zhu, 2007; Shanker & Venkateswarlu,
2011; Gürsoy et al., 2012; Djanaguiraman & Prasad, 2013).
Together, these effects reduce plant growth, development
and survival (Rasool et al., 2013; Hameed et al., 2014).
Food legumes are relatively salt sensitive compared
with cereal crops, thus farmers do not consider growing
food legumes in salinized soils (Saxena et al., 1993;
Toker & Mutlu, 2011; Egamberdieva & Lugtenberg,
2014). The sensitivity in legumes may be due to salt
affecting bacterial activity and nitrogen fixation
(Materne et al., 2007; Toker et al., 2007a; Toker & Mutlu,
2011; Egamberdieva & Lugtenberg, 2014). Salt stress led
to reduction in shoot growth of soybean, chickpea, pea,
faba bean and mung bean plants (Elsheikh & Wood,
1990, 1995; Delgado et al., 1994; Hussain et al., 2011;
Saha et al., 2010; Rasool et al., 2013).
The response of BNF in contrasting tolerance lines of
Medicago ciliaris to salt stress did not show a clear trend
in relation to nodule carbohydrate metabolism (Ben-
Sala et al., 2009). Nodules of common bean (Sassi et al.,
2008) and chickpea (Kaur et al., 2009) display a higher
tolerance to osmotic/salt stress due to increased enzy-
matic antioxidant defence (Arrese-Igor et al., 2011).
Salinity stress significantly decreased the activities of
nitrogenase and phosphate enzymes (acid and alkaline)
in faba bean (Rabie et al., 2005; Hussain et al., 2011). The
effect of salinity stress on growth and some metabolic
activities of mung bean was investigated by Saha et al.
(2010). They concluded that salinity stress suppressed
the early growth of mung bean seedlings. Salinity also
damaged the photosynthetic machinery by causing
reduced chlorophyll content, and also induced the
accumulation of proline, malondialdehyde (MDA) and
H 2 O 2 in roots and leaves of mung bean plants.
Furthermore, salinity stress caused increments in the
activity of superoxide dismutase (SOD), catechol perox-
idase (CPX) and catalase (CAT) in root and leaves of
mung bean plants. Recently, Rasool et al. (2013) reported
that tolerance of chickpea genotypes (SKUA-06 and
SKUA-07) to salinity seems to be related to the efficiency
of the enzymatic antioxidants SOD, CAT, ascorbate per-
oxidase (APX) and glutathione reductase (GR) against
accumulation of reactive oxygen species (ROS), which
would maintain the redox homeostasis and integrity of
cellular components.

1.2.2 Legumes under salinity
Salinity is a major abiotic stress limiting germination,
plant vigour and yield of agricultural crops especially in
arid and semi-arid regions (Munns & Tester, 2008; Abdel
Latef & Chaoxing, 2011; Aggarwal et al., 2012; Ahmad &
Prasad 2012a, 2012b; Porcel et al., 2012; Kapoor et al.,
2013; Abdel Latef & Chaoxing, 2014). Approximately
20% of irrigated land worldwide currently is affected by
salinity, particularly in arid and desert lands, which com-
prise 25% of the total land area of our planet (Yeo, 1999;
Rasool et al., 2013). High salinity affects plants in several
ways: water stress, ion toxicity, nutritional disorders,