Agriculture Reference
In-Depth Information
Legumes play an important role in diet and they are
often referred to as 'poor man's meat'. Legumes are an
important source of protein, oil, fibre and micronutri-
ents, and play a vital role in cropping cycles due to their
ability to fix atmospheric nitrogen (El-Enany et al., 2013;
Mantri et al., 2013).
Under conducive environmental conditions, legumes
develop symbiotic associations with arbuscular mycor-
rhizal (AM) fungi, leading to the formation of sites of
phosphorus nutrient exchange called arbuscules
(Parniske, 2008; Mantri et al., 2013).
Biological fixation of nitrogen (N) is considered more
ecofriendly than industrial N fixation because the NH 3
produced in the former process is readily assimilated
into organic forms by the plant (Valentine et al., 2011).
Biological nitrogen fixation (BNF) in legume nodules
occurs with differentiated forms of rhizobia, termed bac-
teroids, within specialized structures called symbiosomes,
inside the host plant cells (Arrese-Igor et al., 2011).
Thus, these symbiotic associations have strongly driven
the investigation and application of biotechnology tools
for legumes (Dita et al., 2006).
It is estimated that crops grown on 90% of arable
lands experience one or more environmental stresses.
Abiotic stress causes more than 50% of crop loss world-
wide (Rasool et al., 2013; Rodziewicz et al., 2014).
'Abiotic stress' is a broad term that includes multiple
stresses (drought, waterlogging, salinity, heat, chilling
and mineral toxicities) and negatively affects the adapt-
ability and yield of legumes. Application of biotechnology
tools to legume crops can help in solving or reducing the
problems resulting from abiotic stress.
This chapter aims to review the main abiotic stresses
that have a negative impact on the production of some
important food legumes. It also summarizes the selec-
tion criteria and available genetic resources for stress
resistance under abiotic stress conditions.
plant (Toker et al., 2007b; Charlson et al., 2009; Khan
et  al., 2010; Toker & Mutlu, 2011; Impa et al., 2012;
Hasanuzzaman et al., 2013; Pagano, 2014). Drought alone
resulted in about a 40% reduction in soybean yield
(Valentine et al., 2011). Faba bean and pea are known to
be drought-sensitive, whereas lentil and chickpea are
known as drought-resistant genera (Toker & Yadav,
2010). Singh et al. (1999) arranged warm season food
legumes in increasing order of drought tolerance:
soybean < black gram < green gram < groundnut < Bambara
nut < lablab < cowpea. Sinclair and Serraj (1995) reported
that legumes such as faba (broad) bean, pea and chickpea
export amides (principally asparagine and glutamine) in
the nodule xylem are generally more tolerant to drought
stress than cowpea, soybean and pigeon pea, which
export ureides (allantoin and allantoic acid).
The symbiotic nitrogen fixation (SNF) rate in legume
plants rapidly decreased under drought stress due to
(i)  the accumulation of ureides in both nodules and
shoots (Vadez et al., 2000; Charlson et al., 2009), (ii)
decline in shoot N demand, (iii) lower xylem transloca-
tion rate due to a decreased transpiration rate, and (iv)
decline of metabolic enzyme activity (Valentine et al.,
2011). Several reports have indicated that drought
stress led to inhibition in nodule initiation, nodule
growth and development as well as nodule functions
(Vadez et al., 2000; Streeter, 2003; Valentine et al., 2011).
The decrease in SNF under drought conditions was
associated with the reduction of photosynthesis rate in
legumes (Ladrera et al., 2007; Valentine et al. 2011).
In many nodules of legumes, water stress resulted in
stimulation of sucrose and total sugars (González et al.,
1995, 1998; Ramos et al., 1999; Streeter, 2003; Gálvez et
al., 2005; Valentine et al , . 2011). This was consistent
with a study on pea mutants, which showed that sucrose
synthase (SS) is essential for normal nodule development
and function (Craig et al., 1999; Gordon et al., 1999).
Drought stress induces oxidative damage in legumes
and this has a harmful effect on nodule performance
and BNF (Arrese-Igor et al., 2011). Some reports suggest
that nodules having an increment in enzymatic antiox-
idant defence can display a higher tolerance to drought/
salt stress in common bean (Sassi et al., 2008) and
chickpea (Kaur et al., 2009). In addition to this, Verdoy
et al. (2006) reported improved resistance to drought
stress in Medicago truncatula by overexpression of ∆-pyr-
roline-5-carbolyate synthetase resulting in accumulation
of high proline levels.
1.2 Legumes under abiotic stress
1.2.1 Legumes under drought
Drought is a type of water stress that is imposed due to
lack of rainfall and/or inadequate irrigation. About 60%
of all crop production suffers from drought conditions
(Grant, 2012; Naeem et al., 2013). For legumes, drought
stress has adverse effects on total biomass, pod number,
seed number, seed weight and quality, and seed yield per
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