Agriculture Reference
In-Depth Information
These technologies have identified specific molecular
markers that may be used in breeding programmes via
marker-assisted selection (MAS) to improve stress toler-
ance (Dita et al., 2006). In legumes, the practical
application of MAS for the genetic enhancement of
resistance or tolerance to stress has been limited.
Schenider et al. (1997) reported that MAS may be useful
to select drought-tolerant common bean.
variation, including callus cultivation and somatic
embryogenesis, has the ability to generate genetic vari-
ation (Larkin & Scowcroft, 1981; Dita et al., 2006). The
ability to produce agronomically useful somaclones via
organogenesis and somatic embryogenesis has been
reported in pea (Griga et al., 1995) and pigeon pea
(Chintapalli et al., 1997).
Indeed, combining mutagenesis techniques with
MAS through TILLING (see Section  1.7.9) will make
mutagenesis more suitable for legume enhancement.
The main problem with these techniques is the high
quantity of individuals required to find the desired trait.
Nevertheless, by using in vitro selection systems this dis-
advantage can be reduced (Dita et al., 2006).
1.7.3 Gene pyramiding assisted by MaS
Pyramiding different resistance or tolerance traits into a
genotype helps plant breeders to achieve resistance to
abiotic stress. In legumes there are numerous examples
of introgression and pyramiding of favorable alleles and
QTLs. However, MAS has been used to help in gene
pyramiding to overcome stresses in only a few cases
(Dita et al., 2006). Nevertheless, Schneider et al. (1997)
indicated that MAS may be useful to select drought-
tolerant common bean.
There are some exceptions where MAS has facilitated
breeding efforts in several legume crops to combat
important biotic stressors (Dita et al., 2006). For example,
MAS was successfully used for the breeding of soybean
resistant to cyst nematode (Diers, 2004), of pinto bean
resistant to common bacterial blight (Mutlu et al., 2005)
and of narrow-leaved lupin ( Lupinus angustifolius L.)
resistant to phomopsis stem blight (Yang et al., 2002)
and anthracnose (Yang et al., 2004). Moreover, when
resistance is conferred by single genes and/or easily
overcome by new pathogen races, the gene pyramiding
strategy facilitated by MAS can be an efficient method
(Dita et al., 2006).
Legume cultivars having appropriate combinations of
resistance and/or tolerance to biotic and abiotic stresses,
achieved through gene pyramiding, could provide durable
resistance, and MAS can be a valuable tool to guide and
identify the pyramiding of these genes (Dita et al., 2006).
The generation of markers based on genes with
altered expression patterns in response to stresses could
result in more effective and targeted MAS. Some of
these genes may be good candidates for future MAS
studies in legumes (Dita et al., 2006).
1.7.5 In vitro selection
In vitro selection is one of the important classical
breeding methods (Svabova & Lebeda 2005) and has
been used for both biotic and abiotic stresses. In legumes,
in vitro selection was applied to alfalfa ( Medicago sativa )
for selection of resistance to Colletotrichum trifolii
(Cucuzza & Kao, 1986), Fusarium oxysporum (Cvikrova et
al., 1992) and Verticillium albo-atrum (Koike & Nanbu,
1997). However, no resistant lines were reported in
these studies (Dita et al., 2006).
Putative stress-resistant lines derived from both con-
ventional breeding and transgenic approaches could be
screened using in vitro selection. This is suitable for some
abiotic stresses, where appropriate screening methods are
unavailable or have low efficiency. Somaclonal variation
and in vitro mutagenesis followed by in vitro selection
offer an alternative way for breeding (Dita et al., 2006).
1.7.6 transcriptomics
Repression of genes or transcriptional activation is an
important tool in the control of stress responses in plants
(Chen et al., 2002; Dita et al., 2006). Thus, identification
of differentially expressed genes is particularly impor-
tant to understand stress responses in plants. To achieve
this objective, tools such as microarrays (Schena et al.,
1995), serial analysis of gene expression (SAGE)
(Velculescu et al., 1995), suppression subtractive hybrid-
ization library (Diatchenko et al., 1996), and quantitative
measurement of transcription factor (TF) expression
have been developed in addition to older techniques
such as Northern blotting (Dita et al., 2006).
In legumes, transcriptomic techniques are useful
ways of breeding to combat environmental stresses. Jain
1.7.4 Somaclonal variation and in vitro
mutagenesis
Tissue culture provides a big range of genetic variation
in plants, which can be incorporated in plant breeding
programmes (Jain, 2001; Dita et al., 2006). Somaclonal
Search WWH ::




Custom Search