Biology Reference
In-Depth Information
Knowledge of the
R1
sequence was exploited
in several ways. A PCR marker specific to the
R1
gene sequence and a closely linked anonymous
marker were used in an association study in a
gene bank collection of 600 potato cultivars. The
R1
was present in approximately 33% of them.
In the association analysis, a highly significant
QTL for resistance to late blight and maturity
was again detected in the
R1
region, and more-
over, the marker alleles associated with increased
resistance and later plant maturity were traced
to an introgression from
S. demissum
(Gebhardt
et al. 2004). Beketova and colleagues (2006)
tested 70 potato cultivars bred mostly within
the former USSR (of which 26 were included
in the study by Gebhardt et al. 2004) for the
presence of
R1,
and they also found a signif-
icant relationship between the presence of
R1
,
late blight resistance, and late maturity. The
R1
gene could be more widespread than expected, as
it was shown in the case of Black's differentials
R5, R6, and R9, which contained
R1
in addition
to
Rpi
genes indicated by their names (Trognitz
and Trognitz 2007; Kim et al. 2011).
R1
analogs
were analyzed by PCRs specific to the
R1
NBS
sequence in
S. caripense
(Trognitz and Trog-
nitz 2005). They have been found recently in
some accessions of
S. demissum
, but also in sev-
eral species of series
Demissa
,
Longipedicellata,
and
Tuberosa,
although none of them has been
shown to be functional so far (Sokolova et al.
2011). Although a majority of contemporary
P.
infestans
isolates are virulent on R1 plants, in
breeding the
R1
could be still a useful marker for
the late blight resistance QTL on chromosome
V and therefore,
R1
- and
R2
-specific markers
were included in a multiplex PCR for marker-
assisted selection (MAS) of potatoes combining
five disease and pest resistance genes (Mori et al.
2011). The
R1
gene can also be useful in that it
was shown to act both in foliage and in tubers of
potato (Park et al. 2005c). The
Avr1
gene encod-
ing the
P. infestans
effector corresponding to the
R1
gene product has been isolated by positional
cloning and shown to have the RXLR motif as
well as to be highly induced during the biotrophic
phase of potato infection (Vleeshouwers et al.
2011a).
R2
R2
was the first
Rpi
gene mapped in a tetraploid
potato population and with use of amplified
fragment length polymorphism (AFLP) markers.
One of the genes introgressed from
S. demissum
was mapped to chromosome IV (Li et al. 1998).
Although less widespread than
R1
,the
R2
gene is
present in some European potato cultivars such
as Eden, Fresco, Naturella, Pentland Dell, and
Rector. The
R2
was shown to provide a delay in
disease onset in field trials in France even though
virulent isolates were found in the French popu-
lation of
P. infestans
(Pilet et al. 2005).
The second gene mapped to the same
locus,
R2-like
, could not be phenotypically
distinguished from the
R2
but was identified in
the mapping population that did not contain
S.
demissum
in the pedigree (Park et al. 2005d).
Another two genes,
Rpi-blb3
and
Rpi-abpt
,
originated from
S. bulbocastanum
, a 1 EBN
(endosperm balance number) species that could
not be crossed directly with the potato (Park et al.
2005a, b, d). However, while the
Rpi-blb3
was
mapped in an intraspecific
S. bulbocastanum
cross, the
Rpi-abpt
was mapped in advanced
breeding material, in which the resistance - most
likely from
S. bulbocastanum
- was introgressed
into the potato gene pool by bridge crossing four
species:
S. acaule
(A),
S. bulbocastanum
(B),
S.
phureja
(P), and
S. tuberosum
(T) (Hermsen and
Ramanna 1973). These materials were involved
in the potato breeding programs that yielded at
least five cultivars: Biogold, Bionica, Kibama,
Kisoro, and Suprema (Web site for Potato Pedi-
gree Database, Wageningen University:
http:
The
Rpi-abpt
gene was shown to function only
in potato foliage (Park et al. 2005c).
Rpi-blb3
and
Rpi-abpt
have been isolated by
map-based cloning, and
R2
and
R2-like
by allele
mining; and they all belonged to the leucine
zipper (LZ)-NBS-LRR gene family. Something
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