Legumes and breeding under abiotic stress: An overview - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 4

Several criteria have been used in screening for
salinity tolerance including germination, radicle length,
dry weight production, shoot length, cell survival, plant
biomass, nodulation, number of pods, grain yield and
K + /Na + ratio (Toker et al., 2007a; Flowers et al., 2009;
Toker & Mutlu, 2011).

food legumes, faba bean is more tolerant to waterlog-
ging than lentil, pea and chickpea (Siddique, 2000).
Many management practices used to reduce the
effects of waterlogging involve paddock selection, sow-
ing time, seeding rate and drainage (Toker & Mutlu,
2011). Genetic variation in waterlogging tolerance in
food legumes deserves attention (Toker et al., 2007a;
Toker & Mutlu, 2011).

1.2.3 Legumes under waterlogging
Waterlogging occurs when water enters the soil faster
than it can drain away under gravity. Waterlogging is a
major abiotic factor causing losses in food legumes
(Toker & Mutlu, 2011; Ashraf, 2012; El-Enany et al.,
2013). It negatively affected germination, seedling
emergence, root and shoot growth, and plant density by
up to 80%, besides causing seedling diseases (Toker &
Mutlu, 2011).
When mung bean plants were subjected to waterlog-
ging stress, the activities of various enzymatic antioxidants
such as SOD, CAT, APX and GR decreased markedly
(Ahmed et al., 2002). These authors also stated that
oxidative damage was not directly involved in the impair-
ment of photosynthetic machinery of plants under
waterlogged conditions. In contrast, increase in the activ-
ities of different enzymatic antioxidants - SOD, CAT,
peroxidase (POD) and APX - was recorded in pigeon pea
genotypes when subjected to varying degrees of water-
logging stress (Kumutha et al., 2009).
El-Enany et al. (2013) carried out a pot experiment
with three replicates of 75% and 50% water deficit
(WD) and one-fold field capacity waterlogging (WL) on
cowpea ( Vigna sinensis ) plants. The data revealed that
both stresses significantly decreased the fresh and dry
weights of roots and shoots, number of nodules per
plant and nitrogenase activity. Antioxidant metabolites
like phenolic compounds, ascorbic acids, proline, MDA
and H 2 O 2 were significantly increased under WD and
WL. The activities of certain antioxidant enzymes (SOD,
CAT and APX) under both stresses were determined
(El-Enany et al., 2013).
Waterlogging reduces the endogenous levels of nutri-
ents in different parts of the plant (Ashraf et al., 2010,
2012). Oxygen deficiency in the root zone causes a
marked decline in the selectivity of K + /Na + uptake and
impedes the transport of K + to the shoots (Ashraf et al.,
2012). When Medicago sativa was subjected to flooding
stress, a marked reduction in leaf and root nutrient
composition (P, K, Ca, Mg, B, Cu and Zn) was recorded
in plants (Smethurst et al., 2005). Among cool season

1.2.4 Legumes under temperature
extremes
Temperature is one of the major factors affecting the yield
and quality of legumes (Christophe et al., 2011). Heat
stress often is defined as high temperatures that cause
irreversible damage to plant function or development after
a certain period of exposure (Bhattacharya & Vijaylaxmi
2010; Hasanuzzaman et al., 2013). Plants can be damaged
in different ways by either high day or high night tem-
peratures, and by either high air or high soil temperatures.
Also, crop species and cultivars differ in their sensitivity
to high temperatures. High temperature may negatively
affect photosynthesis, respiration, water relations and
membrane stability, and also modulate levels of hormones
and primary and secondary metabolites. Furthermore,
throughout plant ontogeny, enhanced expression of a
variety of heat-shock proteins, other stress-related pro-
teins, and production of ROS constitute major plant
responses to heat stress (Bhattacharya & Vijaylaxmi,
2010; Hasanuzzaman et al., 2013).
Cool-season annual species are more sensitive to hot
weather than warm-season annuals (Hall, 2001). Heat
stress affected nitrate assimilation in legumes by low-
ering synthesis of ureides and decreasing levels and
activities of nitrate reductase and glutamate synthase
(Hungria & Vargas, 2000; Christophe et al., 2011). In
nodules, heat stress may either affect nitrogenase
activity leading to decreased N 2 fixation efficiency or
accelerate nodule senescence resulting in reduced
nodule longevity (Bordeleau & Prévost, 1994; Hungria &
Vargas, 2000; Christophe et al., 2011).
Chilling stress is usually limited to plants that are
native to or growing in tropical or subtropical regions
of the world. Plants vary greatly in their sensitivity to
chilling stress. Chill-sensitive plants have been defined
as plants that are killed or injured by temperatures up
to 15-20 °C above the freezing point of the tissues
(Bhattacharya & Vijaylaxmi, 2010; Hasanuzzaman
et al., 2013). Chill-resistant plants can grow at