Biotechnology approaches to overcome biotic and abiotic stress constraints in legumes - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 249

Though the importance of legumes is unmatched
among all the classes of plants, the biological and
physical threats they face are equally significant. To
their advantage, the morphological and genetic diver-
sity of legumes is very well documented. Variation in
genes involved in floral ontogeny, seed dormancy, root
mass, harvest index and other morphoagronomic traits
has led to establishing the phylogenetic relationships
among the various members of this family. Moreover,
certain genes involved in biochemical processes,
including the alcohol dehydrogenase gene and the
plastid-encoded Matk gene, among others, have helped
in simplifying the genetic, developmental and evolu-
tionary relationships of legumes. This understanding of
leguminous plants helps in identifying the targets that
can potentially be exploited for controlling the response
to various stress factors that can threaten the plants.

by viral infections. The significant infections are caused
by soybean mosaic virus (transmitting through the
seeds) and tobacco ring spot virus (Zhang et al., 2012;
Sastry, 2013). Similarly, black gram and mung bean are
infected by yellow mosaic virus (Vargas et al., 2013).
The virus, transmitted by the whitefly Bemisia tabaci ,
causes the appearance of irregular yellow and green
patches on the plant, ultimately causing the total
deterioration of the plant system. Other viral agents
infecting leguminous plants include beet western
yellow virus, subterranean clover red leaf virus and
other luteoviruses, cucumber mosaic virus, bud necrosis
virus and cowpea golden mosaic virus (Jones, 2012;
Makkouk et al., 2012).

15.3.1.2 Bacterial diseases
Bacterial infections in legumes are relatively limited
compared to viral and fungal infections. Pseudomonas
syringae and Xanthomonas campestris have been associ-
ated with bacterial blight and bacterial pustule in
soybean plants (Baltrus et al., 2012; Khare & Khare,
2012). Blight and pustule are usually observed in the
cool, high altitudes and humid, tropical environments,
respectively. Bacterial wilt is commonly observed in the
groundnut; it is caused by the R. solanacearum and
manifest as the damping and killing of seedlings (Van
der Linden et al., 2013). These bacterial infections may
be spread by infected plant material, infected seeds,
contaminated nutrient sources and water. The bacterial
sources can be effectively controlled by appropriate
handling techniques.

15.3 Legumes in stressed
environments

Legumes, like other plants, are continuously exposed to
many biological and environmental stimuli, which may
have harmful effects on plant growth. These detriments,
alone or in combination, generate a series of events that
significantly affects plant physiology. Some of the biotic
and abiotic constraints affecting legumes are discussed
here.

15.3.1 Biotic stress
Legumes, like other domesticated plant varieties, when
exposed to a biological threat suffer a decrease in overall
agricultural output. These conditions are mainly
observed in response to attack by a variety of patho-
genic organisms including viruses, bacteria, fungi,
insects and other infestations.

15.3.1.3 Fungal diseases
Due to the widespread geo-distribution of the legumes,
a variety of different fungal species infect legumes
according to their habitat. A number of fungal species,
including Phakopsora pachyrhizi, Pythium ultimum,
Fusarium oxysporum and Phytophthora sojae , are
established causes of infections in soybean (Tyler, 2007;
Goellner et al., 2010; Wei et al., 2010; Zhang et al., 2010).
Wet rust and rotting of seedlings and roots are the most
important diseases, responsible for significant economic
losses in soybean crops. Similarly, the important fungal
diseases infecting lentils are dry root rot ( Macrophomina
spp.), vascular wilt ( Fusarium spp.) and pythium root rot
( Phythium spp.) (Singh & Azam, 2010; Mohammadi
et al., 2011; El-Hassan et al., 2013). The fungal diseases of
groundnut include root diseases, foliar diseases, seed

15.3.1.1 Viral diseases
Some of the major viral infections of legumes are
observed in peas. More than 20 different plant viruses
have been identified in peas, and the pea seedborne
mosaic virus (PSbMV), pea/bean leaf roll virus
(P/BLRV) and pea enation mosaic virus (PEMV) are of
major economic importance (Vemulapati et al., 2011;
Makkouk et al., 2012; Maury et al., 2012). Infections
can have disastrous financial impacts for the farmer.
Soybean, a major economic commodity, is also affected