Organization of Genes Conferring Resistance to Anthracnose in Common Bean - Translational Genomics for Crop Breeding: Biotic Stress - page 174

genes, although a monogenic segregation is
observed in the response to specific races.
6. Anthracnose resistance genes are located in
specific regions of genome and they are orga-
nized in groups or gene clusters in which each
gene confers resistance to one specific isolate
or race.
7. Description of alleles at locus based on resis-
tance profiles should be reconsidered because
different and linked loci can be involved in the
resistance reaction against different races or
isolates in a bean genotype.
8. Many resistance loci are organized in clusters
of closely linked genes since recombination
between resistance genes has been detected.

LinkageGroupPv08

A BAC from the bean genotype Sprite harboring
part of the Co-4 gene was sequenced and assem-
bled in a single contig of 106.5 kb. Five copies of
the COK-4 gene that encodes for a LRR-Kinase
and 19 novel genes with no similarity to any pre-
viously identified genes were described (Melotto
et al. 2004).

LinkageGroupPv11

A gene family encoding for LRR sequences
located in the vicinity of the Co-2 locus was
characterized in the genotype EO 2 (Geffroy et al.
1998; Creusot et al. 1999). The PvH20 clone con-
tains six sequences for LRR motifs, suggesting
that the PvH20-related sequences may be candi-
date genes conditioning resistance for anthrac-
nose on Pv11. Recent analysis of the genomic
region containing the Co-2 resistance locus in the
BAT93 genotype revealed the presence of clus-
ters of sequences coding for Coiled-coil-NBS-
LRR (Chen et al. 2011).

Implications

Implication in Genetic Analysis of
Anthracnose Resistance

The authors suggest that the following guidelines
are to be followed in the future characterization
of all genes conditioning resistance to C. linde-
muthianum in common bean.

Conclusions

Researchers should base future characteriza-
tion of new resistance sources on multiple
inoculations of families (F 2:3 or later gener-
ations) or RIL populations, instead of relying
on single races inoculated on single F 2 plants.

Evidence about C. lindemuthianum -common
bean interaction suggests:

1. Anthracnose resistance in bean genotype(s) is
generally controlled by major genes exhibit-
ing a race-specific mode of action.
2. Interaction of C . lindemuthianum genotype
with the bean genotype seems to be very
specific.
3. Classification of the variation of C . lin-
demuthianum into races is limited. Addi-
tional variation can be found within races or
pathogenic variants.
4. Resistance response against a specific iso-
late/race can be controlled by different loci
in common bean.
5. Genetic control of anthracnose resistance
against different isolates or races in a bean
genotype

Researchers should choose a number of differ-
ent pathogenic races/isolates to screen both the
RxS and RxR populations. The authors recog-
nize that the choice of races will depend on
reaction of new resistance sources, but every
attempt should be made to select a number of
specific races and bean genotypes at each gene
cluster on the seven known linkage groups
in order to truly characterize new resistance
source (tagging of clusters using races). Since
different races and bean genotypes were used
to characterize specific genes on specific link-
age groups, some of these key races need to
be selected when conducting complementary
testing. Different races inoculated on the same can be controlled by different