Biology Reference
In-Depth Information
resistance source have been shown to iden-
tify specific genes on different linkage groups,
so the random use of races in complementary
testing is not recommended.
Researchers should also consider verifying the
co-segregation or linkage between molecular
markers linked to known genes and the new
resistance locus in order to verify that new
resistance genes identified in a bean genotype
do not reside at a known resistance cluster
(tagging of clusters using molecular markers).
imprecise description of this plant-pathogen
interaction. A new system for naming Co-genes
is being proposed that provides critical additional
information to describe the specific interaction
between
C. lindemuthianum- P. vulgaris
and the
relative position in the bean genetic map. The
authors suggest that the new system of nomen-
clature should consider the relative position on
the genetic map (resistance cluster), the geno-
type of the pathogen (isolates or race), and the
bean genotype in which the resistance gene was
identified. The regions containing anthracnose
resistance genes would be named following the
classical nomenclature based on the Co-genes:
clusters Co-1 (Pv01), Co-2 (Pv11), Co-3(Pv04),
Co-4 (Pv08), Co-5 (Pv07), Co-13 (Pv03),
and Co-u (Pv02). The specific resistance gene
included in each resistance cluster would be
named, using a superscript indicative of the iso-
late or race and the bean genotypes in which
the gene was identified. For example, the genes
conferring resistance to isolates CL18 and CL63
(races 38 and 6) in the Cornell 49242 bean geno-
type located in the relative position of Co-2 clus-
ter would be named as genes
Co-2
38 CN
and
Co-
2
6CN
, respectively. The gene conferring resis-
tance to isolate CL18 (race 38) in the Widusa
bean genotype located in the relative position of
the Co-3 cluster (Rodrıguez-Suarez et al. 2008)
would be named as
Co-3
38 WD
and variety abbre-
viations would be provided.
Implication for Plant Breeding
Classification of
C. lindemuthianum
into
pathogenic races using a set of different bean
genotypes may mask true pathogenic variation.
Breeders should use their local isolates and
should identify resistance sources against the
local isolates in the development of their plant-
breeding programs. Genetic analysis of resis-
tance against new isolates is also recommended
in known and unknown resistance sources to ver-
ify the genes involved in the resistance reaction.
The existence of intra-cluster recombina-
tion can be of considerable practical impor-
tance. Race-specific resistance genes present
in different haplotypes of the same cluster
could be pyramided by genetic recombination
within the cluster. For example, intra-cluster
recombination was used to pyramid resistance
loci located on cluster Co-3 from Widusa
(S19;R65;R73;R102;R449;S31) and Mexico
222 (R19;S65;S73;S102;S449;R31) into the line
MexW1 (R19;R65;R73;R102;R449;R31). After
accumulating the resistance specificities, the
enhanced new recombinant haplotype could be
introgressed into susceptible varieties, practi-
cally as a single locus (A Campa unpublished
data). Gene pyramiding is essential for the long
term control of this highly variable pathogen.
Future Prospects
Genomic sequence projects and analysis of
expressed sequence tags (ESTs) are providing
an enormous enrichment of databases
(http:
Langridge and Fleury 2011). Advances in
“omics” technologies are also providing new
tools for breeders and geneticists such functional
molecular markers or fine genetic maps. Func-
tional markers (FMs) derived from polymorphic
sites within gene-coding sequences causally
affecting phenotypic trait variation are more
reliable
Implication for Gene Nomenclature
The current nomenclature system only recog-
nizes
major
Co-genes,
which
may
result
in
for
identification
and
selection
of
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