Microbial strategies for the improvement of legume production in hostile environments - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 134

yield and nodulation when co-inoculated with plant-
growth-promoting rhizobacteria (PGPR) under hostile
environmental conditions compared to inoculation with
rhizobia alone (Rokhzadi et al., 2008; Yang et al., 2009;
Jabborova et al., 2013b).
This chapter examines recent studies on the impact of
salt and drought stresses on legumes and the genotypic
variation among legumes for germination, seedling
growth and other plant traits under hostile conditions,
and the microbial technologies that can improve growth,
development and symbiotic performance of legumes. In
addition, some possible mechanisms of plant resistance
to stress, growth stimulation and improved symbiotic
performance by rhizobacteria are described.

reduces the growth of roots and root hairs, thereby
decreasing sites for potential rhizobial infection and
further nodule development (Katerji et al., 2001;
Bouhmouch et al., 2005). The decrease in root growth
was related to endogenous levels of phytohormones
such as gibberellins, abscisic acid, jasmonic acid and
salicylic acid, which declined under NaCl-induced salt
stress (Debez et al., 2001).
Several reports have indicated that germination and
seedling growth of chickpea are reduced in saline soils,
with responses varying according to cultivars (Gandour,
2002; Al-Mutawa, 2003). Krouma (2009) evaluated
the growth, nodulation, nitrogen fixation and ionic
repartition in two chickpea varieties, and found that
the salt-tolerant cultivar was able to protect its photo-
synthetic and symbiotic apparatus against the toxic
Na + and Cl − ions.
We have also observed a significant effect of salinity
(salt concentration) on germination, and on shoot and
root length of chickpea genotypes (Table 9.1). The 29
genotypes differed significantly for germination and
shoot and root length. There was a significant geno-
type × salinity interaction on germination and shoot and
root length. According to Almansouri et al. (2001), seed
germination is usually the most critical stage in seedling
establishment. Acccording to Sadiki and Rabih (2001),
chickpea is a salt-sensitive species, and conditions of
25 mM NaCl resulted in a 71% reduction in growth. We
have also observed that most chickpea genotypes were
salt sensitive, with germination capacity decreasing with
increasing salinity. The present result agrees with the
work of Gandour (2002) and Vadez et al. (2007), who
observed decreases in percentage germination and seed-
ling emergence of chickpea with increases in salinity.
Atak et al. (2006) and Neamatollahi et al. (2009) pointed
out that higher salinity may reduce germination due to
higher osmotic pressures. The seeds of six chickpea geno-
types, namely Jahongir, Uzbekiston-32, Lazzat, Zimistoni,
Flip 1-22 and Flip 1-31, showed better germination (40-
45%) than other chickpea genotypes. According to
Tejovathi et al. (1988) the ability of a seed to germinate
under salt stress indicates that it has genetic potential for
salt tolerance. The 29 genotypes of chickpea differed in
their response to different salinity levels (Table 9.2).
The reduction in seed germination rate (at 10 days
after sowing), as compared to the respective controls,
was less than 25% for Sino, Flip 1-01, Flip 1-04, Flip
1-05, Flip 1-19, Flip 03-27c and Flip 06-155c. Seeds of

9.2 abiotic stresses affecting
legume crop productivity

9.2.1 plant growth and stress
Previous studies have shown that soil salinity and
drought decrease rhizobial colonization, inhibit infec-
tion processes and nodule development, and reduce N 2
fixation and nitrogenase activity in legumes (Zahran &
Sprent, 1986; Zahran, 1999; Kulkarni et al., 2000; Serraj,
2002; Egamberdieva et al., 2013b). In earlier reports
the inhibition by salinity of growth, nodulation and
N fixation was observed in chickpea (Singh et al., 2001),
common bean (Ferri et al., 2000) and lentil (Golezani &
Yengabad, 2012). In subsequent studies, saline soil
conditions inhibited germination and seedling growth,
nodulation and biomass accumulation in soybean (Essa,
2002; Li et al., 2006). Similar findings were observed for
soybean by Hamayun et al. (2010), where the plant
length, biomass, chlorophyll content, number of pods,
100-seed weight and yield were all significantly reduced
by salinity stress. Leaf chlorosis, leaf bleaching and
necrosis were also observed as effects of salt stress on
soybean (Parker et al., 1987). In lentil, plant growth and
nodulation were significantly reduced over the whole
growing season under saline soil conditions (Van Hoorn
et al., 2001). The decreased nodule formation resulted in
reduction of leghaemoglobin content and N 2 fixation
activity (Parida & Das, 2005). Limitation of oxygen dif-
fusion in the nodules could be the reason for inhibition
of nitrogenase activity and respiration of the nodules
(Serraj et al., 1995). Further, salt stress affects protein
synthesis, lipid metabolism and photosynthesis, and