Resistance to Late Blight in Potato - Translational Genomics for Crop Breeding: Biotic Stress - page 231

a parent of the mapping population was shown
to be stacked with four Rpi genes ( R3a, R3b,
R4, and R8 ), while the R8 gene was also present
in the R9 differential. However, the contribution
of the R8 gene to resistance was remarkable in
recent field trials (Kim et al. 2011).

the F locus, which can serve as a phenotypic
marker in addition to molecular ones ( Sliwka
et al. 2012b).
Apart from R genes, a number of QTLs for
resistance to P. infestans have been mapped to
potato chromosome X (Oberhagemann et al.
1999; Sliwka et al. 2007; Danan et al. 2009).
These QTLs originate from various Solanum
species, including S. sparsipilum , which is a
synonym of S. ruiz-ceballosii (Danan et al.
2009). A QTL meta-analysis that allowed more
precise comparisons of different genetic maps
has identified two meta-QTLs for late blight
resistance on potato chromosome X. The Rpi-
ber1 / R Pi-ber is located between them and the
Rpi-ber2 localization overlaps with a meta-
QTL named MQTL_2_Late_blight (Danan et al.
2011).

R ber
The first Rpi gene mapped on chromosome
X originated from S. berthaultii (Ewing et al.
2000). The same gene, later named R Pi-ber ,was
mapped more precisely to a distance of 4.6 cM
from the marker TG403 (Rauscher et al. 2006).
When isolates of P. infestans compatible with
R Pi-ber were used for inoculation, a smaller but
significant resistance effect was detected in the
same map position as the R gene. This could
be explained by the residual effect of the gene
or/and a resistance QTL located in the same
position (Rauscher et al. 2010). The R Pi-ber gene
proved to be effective in both foliage and tubers
(Mayton et al. 2011). In a breeding experiment on
the effects of pyramiding of the R genes, men-
tioned in the R2 section of this chapter, R Pi-ber
was used, together with the R Pi-mcd1 gene, and
both genes showed an additive effect on resis-
tance to late blight in a field test. A larger effect
was provided by the R Pi-ber , which produced
a three-week delay in infection reaching 50%
of the leaf area (Tan et al. 2010). In the same
species, S. berthaultii, two more R genes, Rpi-
ber1 and Rpi-ber2 , were identified and mapped
to chromosome X (Park et al. 2009). Park and
colleagues speculate that, on the basis of location
and origin, Rpi-ber1 (Park et al. 2009) may be
identical to R Pi-ber (Rauscher et al. 2006). Rpi-
ber2 is most likely a different gene, although
located in a similar position 12 cM north of the
marker TG403 (Park et al. 2009). Recently, an
Rpi-rzc1 from S. ruiz-ceballosii (syn. S. spar-
sipilum ) was mapped to the same location with
use of Diversity Array Technology. It provided a
high level of resistance to P. infestans in detached
leaflet, tuber slice, and field tests. Remarkably it
was linked to the violet flower color encoded by

R3

This gene from S. demissum was the first one
mapped to chromosome XI (El-Kharbotly et al.
1994). It was soon followed by R6 and R7, origi-
nating from the same species (El-Kharbotly et al.
1996). High-resolution mapping of R3 combined
with precise phenotyping with specific P. infes-
tans isolates brought a discovery that there are
actually two closely linked genes with distinct
specificities, R3a and R3b (Huang et al. 2004).
These two genes were subsequently shown to
be CC-NBS-LRR genes with 82% of nucleotide
identity (Huang et al. 2005; Li et al. 2011).
Genes R5, R6, R7, R8, R9, R10, and R11 were
all suspected to be alleles of the same locus on
chromosome XI (Huang 2005). Apart from R6
and R7 mentioned above, the localization of R10
and R11 was also confirmed by mapping (Brad-
shaw et al. 2006), but R8 has more recently been
mapped to chromosome IX (Jo et al. 2011). A
functional homolog of R3a - Rpi-sto2 -was
identified in S. stoloniferum (Champouret 2010).
The region on chromosome XI that contained the
described Rpi genes was shown in several studies
to also harbor the QTL for resistance to P. infes-
tans and for maturity, introduced from diverse