Agriculture Reference
In-Depth Information
Pedigree breeding
Backcrossing
Parent A
Resistant parent
Recurrent parent
Resistant parent
F
1
Recurrent parent
F
1
Recurrent parent
B
1
F
1
F
2
Recurrent parent
B
2
F
1
B
3
F
1
F
3
B
3
F
2
F
4
Mass selection
Single backcross or topcross
Parent A
Resistant parent
Parent A
Resistant parent
F
1
F
1
Parent A or B
F
2
B
1
F
1
/ F
1
F
3
F
2
F
4
/F
5
or later
F
2
progeny method
Parent A
Resistant parent
F
1
F
2
Limited or random selection
F
3
F
4
F
5
Figure 6.1
Some basic breeding techniques for self-pollinating crops.
Where diseases are generally less important, but have potential for severe damage
under specifi c conditions, then a sensible strategy is for breeding programs to simply
avoid the use of highly susceptible parents or to only select against those breeding lines
that are highly susceptible.
6.4.1
Phenotypic and marker-assisted selection (MAS)
Until the development of molecular markers, almost all selection for disease resistance was
conducted through the phenotypic evaluation of breeding lines in the presence of disease.
In a few instances, known linkages with other traits or pleiotropy, as in the case of leaf tip
necrosis and the minor genes
Lr
34/
Yr
18 for leaf and stripe resistance, respectively, have
been used. Cytogenetic methods and chromosome staining have also been used to identify
resistant lines carrying introgressed chromosomal segments from related species.
