Legumes and breeding under abiotic stress: An overview - Legumes Under Environmental Stress: Yield, Improvement and Adaptations - page 7

Development Centre (AVRDC) was established for the
improvement of mung bean worldwide. Besides, the US
Department of Agriculture (USDA) has focused research
activities on soybean. The Indian Institute of Pulses
Research, Kanpur, a leading centre of the Indian Council
of Agriculture Research, and other Agriculture
Universities in India are also involved in genetic improve-
ments in warm season legume crops, including pigeon
pea, mung bean and urd bean. These national and inter-
national centres are involved in collection, evaluation
and sharing of germplasm, and also undertake breeding
programmes for genetic improvement. The international
centres also distribute the segregating populations and
inbred lines to partner countries for selection and release
as varieties, resulting in stimulation of breeding interna-
tionally. Hall et al. (1997) and Singh et al. (1997) have
described cowpea breeding programmes in different
regions of the world. The bean/cowpea CRSP (Cowpea
Collaborative Research Program) is also catalysing and
supporting research on cowpea improvement in the
USA, Cameroon and Senegal. Significant research on
various aspects of cowpea improvement is also being car-
ried out in Brazil, Nigeria, Burkina Faso, Senegal, Mali
and India and, to a lesser extent, in a number of other
countries. These efforts have led to the development of
different types of cowpea cultivar, including Vigna
unguiculata , Vigna biflora (or catjang) and Vigna sesquipe-
dalis (Hall et al., 1997).

association of photosensitivity has been observed with
dwarfing, which is controlled by a single recessive gene
(Ishiyaku & Singh, 2001). In urd bean, earliness and
photo-thermosensitivity are recessive traits and are con-
trolled by major genes (Sinha, 1988). Thus selection of
genotypes with early vigour holds tremendous impor-
tance in breeding programmes. As a result, some of the
very popular early varieties, such as Narendra Urd 1, KU
300, Sarla, Vamban and Urd 3, have been developed in
India for commercial cultivation. Since urd bean is also
cultivated in the spring/summer season, Pant U 19, T 9,
KM 1 and TMV 1 have been developed as photo-ther-
moinsensitive varieties (Gupta & Kumar, 2006).

1.6.2 Leaf pubescence density
Suitability for soybean cultivation is improved by this
trait in drought-prone areas, as it reduces leaf tempera-
ture and water loss by transpiration and enhances
photosynthesis and vegetative vigour (Du et al., 2009).
Two additive genes control this trait in soybean (Pfeiffer
& Pilcher, 2006). This is also an important trait of mung
bean and urd bean; some lines of mung bean developed
at AVRDC, e.g. V 2013, V 1281, V 3372, VC 1163D, VC
2750A, VC 2754A and VC 2768A, can withstand mois-
ture stress (Tickoo et al., 2006), including long spells of
rainfall causing flooding.

1.6.3 Seed dormancy
Reduced seed dormancy is found in mung bean, result-
ing in preharvest sprouting during the maturity phase in
the monsoon ( kharif ) season. Therefore the identification
of lines with tolerance to preharvest sprouting is highly
desirable, both in this crop (Tickoo et al., 2006) and in
urd bean.

1.6 Breeding of warm season food
legumes under abiotic stress

Singh et al. (2011) summarized some important target
traits in breeding programmes for improving the warm
season food legumes against abiotic stress, as detailed
below.

1.6.4 Deep root system
Many desert plants have been reported not to have a
deep root system, whereas deep rooting becomes more
common in less extreme dry areas (Vadez et al., 2007).
In fact, the importance of any aspect of rooting pattern
(depth, depth distribution, root length density, etc.) is
totally relative to the distribution and amounts of water
or nutrients in the soil profile. For example, increased
root depth/root volume is useful only where there is
significant water available to exploit by increasing the
soil volume explored by the roots (Vadez et al., 2007).
Kashiwagi et al. (2006) showed the importance of
roots for seed yield under terminal drought conditions

1.6.1 Short duration and photo-thermal
insensitivity
These are important traits in soybean, mung bean and
urd bean, because the development of short-duration
and photo-thermally insensitive genotypes creates
plants suitable for different cropping systems, and also
avoids terminal drought (Singh et al., 2011). In cowpea,
photosensitive cultivars not only flower early but also
become extremely dwarf in habit when day length is
under 12.5 h (Ishiyaku & Singh, 2001), and a complete