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HORTSCIENCE 43(1):200–202. 2008.
Black Currant Clonal Identity and
White Pine Blister Rust Resistance
Todd A. Burnes and Robert A. Blanchette
Department of Plant Pathology, University of Minnesota, 495 Borlaug Hall,
1991 Upper Buford Circle, St. Paul, MN 55108
Jason A. Smith
1
School of Forest Resources and Conservation, University of Florida,
134 Newins-Ziegler Hall, P.O. Box 110410, Gainesville, FL 32611
James J. Luby
Department of Horticultural Science, University of Minnesota, 1970 Folwell
Avenue, St. Paul, MN 55108
Additional index words. Ribes nigrum, white pine blister rust, rust fungus, immunity, forest
pathology, alternate host, Pinus strobus
Abstract. Gooseberries and currants (Ribes L.) are the alternate hosts for the fungus
Cronartium ribicola J. C. Fischer, the causal agent of white pine blister rust. In this study,
16 black currant (R. nigrum L.) cultivars, including three accessions of the putatively
immune cultivar ‘Consort’ and three cultivars developed at the University of Minnesota
Horticultural Research Center, were screened for resistance to C. ribicola using artificial
inoculation procedures. Twelve of these cultivars were grown in the field and observed
for natural infection. Cultivars ‘Ben Sarek’, ‘Ben Lomond’, and ‘C2-2-1’ were infected
naturally in the field at the University of Minnesota Horticultural Research Center in
2000, 2001, and 2004. Cultivars ‘Ben Sarek’, one mislabeled ‘Consort’ accession,
R. nigrum ‘WI-1’, and ‘Ben Lomond’ had significantly more uredinial sori than other
cultivars when inoculated artificially. To determine if the infected and noninfected
‘Consort’ clones were genetically related, DNA microsatellite genotyping was carried out
to fingerprint these clones. One of the six microsatellite loci resulted in a polymorphism
that indicated the infected clone was genetically different from the noninfected clones. In
addition, the inoculation procedures used in these studies are generally efficacious for
predicting resistance in the field because none of the field-infected cultivars were
resistant in the greenhouse. This study confirms the Cr gene for resistance to C. ribicola
in Ribes has remained effective for over 50 years.
Gooseberries and currants belong to the
genus Ribes and include many native species
and cultivars used for ornamental plantings
and fruit production in North America. Breed-
ing programs in North America and Europe
have focused on producing Ribes with
desired juice quality, winter hardiness, cul-
tural characteristics, and pest resistance,
including tolerance to insects, viruses, and
fungi (Brennan, 1995; Dale, 2000; Hummer
and Barney, 2002).
Several native and nonnative species of
Ribes can serve as alternate hosts for Cro-
nartium ribicola, the causal agent of white
pine blister rust (WPBR). This disease was
introduced into North America over 100 years
ago and has caused major mortality to native
five-needle pines. Once the Ribes leaves are
infected with aeciospores from the pine, they
develop uredinia that produce urediniospores
that reinfect Ribes leaves during the summer
months (Sinclair et al., 1987). This is fol-
lowed by the production of telia and basidia
in late summer and fall. Basidiospores from
basidia do not travel long distances and infect
pines through needle stomata (Sinclair et al.,
1987). One method of control of this disease
in the United States and Canada has been to
eradicate native and cultivated susceptible
Ribes in areas where five-needle pines grow.
This has been discontinued because of its cost
and lack of evidence that eradication was
successful to reduce the incidence of WPBR
(Maloy, 1997). Fifteen states have regula-
tions that prohibit selling or planting of cer-
tain Ribes species or cultivars, particularly
the nonnative European black currant,
R.nigrum, that has been found to be extremely
susceptible to WPBR (Barney and Hummer,
2005; McKay, 2000). One source of immunity
to C. ribicola in Ribes originates from the
dominant Cr gene derived from R.ussuriense
(Knight et al., 1972). Ribes ussuriense is very
closely related to R. nigrum (considered by
some to be a variety) and has been used in
breeding programs to develop immune culti-
vars with characteristics similar to R.nigrum.
There are several named cultivars that origi-
nated this way, including ‘Consort’, ‘Coronet’,
and ‘Crusader’ (Hunter, 1955). Many Ribes
cultivars are sold in nursery centers and pro-
moted for their cultural characteristics and
WPBR resistance. Several field and artificial
inoculation studies have been completed to
determine the relative susceptibility of Ribes
cultivars to WPBR (Hummer, 1997, Pluta
and Broniarek-Niemiec, 2000; Zambino,
2000). After field evaluations, a red currant
(Ribes rubrum L.) cultivar, ‘Viking’ was
thought to have immunity to C. ribicola;
however, uredinial sori developed after arti-
ficial inoculations (Zambino, 2000). It was
suggested that an error in labeling or propaga-
tion may have occurred and it was wrongly
designated as immune. Recently, fingerprint-
ing techniques using random amplified poly-
morphic DNA and intersimple sequence repeat
markers have become available to determine
relatedness of Ribes genotypes (Lanham
et al., 2000). This technology is useful for
verifying accuracy of clones and resistant
genotypes.
During a previous study (Burnes et al.,
unpublished data), it was determined that
plants being sold as R. nigrum ‘Consort’ by a
wholesale nursery in the United States were
very susceptible to WPBR after artificial
inoculations. These plants, however, were
being marketed as ‘‘immune.’’ The objec-
tives of this study were to 1) determine the
susceptibility and genetic relatedness of three
‘Consort’ accessions and 2) determine the
WPBR susceptibility of 16 Ribes clones in
the field and after artificial inoculations.
Materials and Methods
Plant materials. Twelve R.nigrum acces-
sions used in this study were collected from a
germplasm planting at the Horticultural
Research Center (HRC), University of Min-
nesota, Chanhassen, MN. These included
clones ‘Ben Lomond’, ‘Ben Sarek’, ‘Con-
sort’ (referred to here as ‘Consort-HRC’),
‘Golubka’, ‘Nadezhnaya’, ‘Titania’, three
experimental selections (‘C2-2-1’, ‘D16-6-54’,
and ‘D16-8-14’) from selections made at the
Scottish Crop Research Institute, and three
selections from the HRC (‘9908 P66’ and
‘9808 P45’) both from the cross (‘Consort’ ·
‘Ben Lomond’) and ‘9907 P66’ (‘Crusader’ ·
‘Ben Lomond’). For artificial inoculations, in
addition to these cultivars, two accessions
[‘Consort’ (PI 556071) (referred to here as
‘Consort-OR’) and ‘Crusader’ (PI 556050)]
were obtained from the U.S. Department of
Agriculture–Agricultural Research Service
(USDA-ARS) National Clonal Germplasm
Repository (Corvallis, OR). Two other
clones, plants labeled as ‘Consort’ (referred
to here as ‘Consort-MN’) were from a local
wholesale nursery in Minnesota and an
unnamed European black currant clone
(referred to here as ‘WI-1’) that previously
has been used in WPBR screening studies at
the University of Minnesota (Jurgens et al.,
2003) were also included in the studies.
Cuttings from the current year’s terminal
growth were taken from each accession used
Received for publication 28 Mar. 2007. Accepted
for publication 24 June 2007.
We are grateful to Dr. Rex Brennan of the Scottish
Crop Research Institute and Dr. Kim Hummer of
the USDA National Clonal Germplasm Repository
for providing plant materials for this study.
1
To whom reprint requests should be addressed;
e-mail jasons@ufl.edu.
200 HORTSCIENCE VOL. 43(1) FEBRUARY 2008
in this study and placed into vermiculite
and kept in a mist chamber until root forma-
tion. After root formation, clones were trans-
planted into four-inch pots containing a high-
porosity soilless growing medium and placed
in a greenhouse with 18 h of light in a 24-h
period with 21 C nighttime and 25 C
daytime temperatures.
Field observations for white pine blister
rust. Plants growing in experimental plant-
ings at the HRC were evaluated for the pres-
ence of natural infection by C. ribicola in
2000, 2001, and 2004. The following 12 R.
nigrum accessions were included in these
evaluations: ‘Ben Lomond’, ‘Ben Sarek’,
‘Consort-HRC’, ‘Nadezhnaya’, ‘Titania’,
‘C2-2-1’, ‘D16-6-54’, ‘D16-8-14’, ‘9908
P66’, ‘9808 P45’, ‘9907 P66’, and ‘Golubka’.
Plants were evaluated for the presence of
uredinial sori on approximately Sept. 5 each
year (Table 1).
Greenhouse inoculations. Urediniospores
(0.1 g) of C. ribicola strain WI4.1B (Jurgens
et al., 2003) were collected from infected
R.nigrum and added to 400 mL of sterile
0.025% purified water agar solution. After
adjusting the spore concentration to 24.4 ·
10
4
spores/mL using a hemacytometer, a
1-mL spore suspension was sprayed onto
the undersides of each of three leaves (leaf
size was 6 to 7 cm in diameter) per plant
using a handheld sprayer (Jurgens et al.,
2003). Four plants with two leaves per plant
for each cultivar were inoculated. After
inoculation, the tops of each leaf were misted
with distilled–deionized water and plants put
into a plastic bag, sealed, and placed into a
dark chamber at a temperature of 20 C for
24 h. A sample of the urediniospore suspension
was also sprayed onto a plate of water agar to
observe germination rate. These plates were
placed into the growth chamber at the same
time and conditions as the plants and re-
moved 24 h after inoculation to calculate
urediniospore germination rate using 40·
magnification. After 24 h, plants were re-
moved from bags and placed into a chamber
at 20 C with a 12-h light period.
After 35 d of incubation, uredinial sori
were counted in an area defined by a 2-cm
diameter ring placed in the center of each of
three apical sections (lobes) per leaf of each
cultivar for a total of 24 areas per cultivar
(Table 2). The presence or absence of telia
was also recorded. The mean number of
uredinial sori that developed on leaves of
the different Ribes cultivars were compared
with Tukey’s multiple comparison using
Statistix 7 (Analytical Software, Tallahassee,
FL) (Table 2).
Microsatellite genotyping. Microsatellite
(simple sequence repeat) markers were used
to determine the genetic relatedness of the
three different accessions of Ribes nigrum
labeled as ‘Consort’. Genomic DNA was
extracted using the Qiagen DNeasy plant
mini-kit (Qiagen, Valencia, CA) according
to the manufacturer’s instructions. Micro-
satellite loci RJL1-RJL6 were targeted for
polymerase chain reaction (PCR) using pri-
mers designed for Ribes nigrum by Brennan
et al. (2002). PCRs were performed using an
MJ Research PTC-100 minicycler (Bio-Rad,
Hercules, CA). PCR amplicons were visual-
ized on 1.5% agarose gels stained with SYBR
I green nucleic acid stain. Results were
photographed using a digital camera and
Dark reader (Clare Chemical Research,
Dolores, CO).
Results
Field observations for Ribes infection by
white pine blister rust. Cultivars ‘Ben Sarek’,
‘Ben Lomond’, and ‘C2-2-1’ were naturally
infected in the field at the University of Min-
nesota HRC and uredinial sori were observed
on the plants in 2000, 2001, and 2004 (Table
1). The cultivar ‘Ben Lomond’ had 75% of
the leaves infected in 2000, 90% of the leaves
infected in 2002, and 90% infected in 2004.
‘Ben Sarek’ and ‘C2-2-1’ had less than 1% of
the leaves infected in all 3 years. The remain-
ing genotypes had no signs of infection
(Table 1).
Greenhouse inoculations. Results from
controlled inoculations showed Ribes culti-
vars ‘Ben Sarek’, ‘Consort-HRC’, ‘WI-1’,
and ‘Ben Lomond’ had significantly more
uredinial sori than did ‘C2-2-1’ and
‘Golubka’ (Table 1). The remaining acces-
sions had no signs of infection. All cultivars
that became infected also developed telia.
The average rate of urediniospore germina-
tion on water agar was 56%.
Microsatellite genotyping. Successful
PCR amplification was obtained for five
of six microsatellite loci tested (RJL1,
RJL2, RJL3, RJL5, RJL6). One of the five
microsatellite loci, RJL2, displayed a poly-
morphism indicating that the infected clone,
‘Consort-MN’, was genetically different
from, but likely related to, the noninfected
clones of ‘Consort’ (‘Consort-HRC and
‘Consort-OR’) (Fig. 1). No polymorphisms
were observed for the other loci.
Discussion
The successful cultivation of Ribes for
fruit production in North America will de-
pend on development and deployment of
C. ribicola-resistant cultivars. The R.nigrum
cultivars ‘Ben Sarek’, ‘Ben Lomond’, and
‘C2-2-1’ in this study demonstrated suscep-
tibility to C. ribicola similar to other results
observed in a previous study (Hummer,
1997). Cultivar ‘Golubka’ developed uedi-
nial sori in the inoculation trials but not in the
field. This may be attributed to the high
inoculum load during artificial inoculation
because ‘Golubka’ is a derivative of R.
dikuscha and a cross between susceptible
‘Saunders’ and resistant ‘Pimorskij Cem-
pion’ cultivars (Brennan, 1995). This cultivar
should be tested on a wider scale to determine
if it will become infected under field con-
ditions. Regional differences in virulence
may occur among strains of C.ribicola, and
the strain used in this study to inoculate
cultivars may differ in virulence than others
found in North America. However, in a study
by Zambino (2000), 21 different strains of C.
ribicola from different states showed no
significant differences in infection on Ribes.
The clones ‘9908 P66’, ‘9907 P66’, and
‘9808 P45’ were selected at the University of
Minnesota HRC because they exhibited no
blister rust infection and had high fruit pro-
ductivity and an upright growth habit suitable
for mechanical harvest. All are from crosses
between the susceptible cultivar ‘Ben
Lomond’ and resistant cultivars, either ‘Con-
sort’ or ‘Crusader’ (Table 1). Their immunity
to WPBR in this study suggests that they may
possess the C.ribicola resistance gene, Cr,
from the ‘Consort’ or ‘Crusader’ (Brennan,
1995; Knight et al., 1972). The Scottish
selections are from crosses involving Ribes
with WPBR-resistant parents. The resistance
they exhibited in the inoculation trials dem-
onstrated that a high level of resistance can be
selected in the field. If this resistance is the
result of Cr, then this resistance gene is still
Table 2. Number of uredinial sori on leaves of
Ribes nigrum cultivars with Cronartium ribicola
inoculated under controlled conditions.
Ribes nigrum L. cultivar
identification
Mean number
of uredinial sori
on Ribes leaves
z
Ben Sarek 135.4 a
Consort-MN-1 121.6 a
WI-1 107.1 a
Ben Lomond 106.2 a
C2-2-1 5.1 c
Golubka 0.7 c
Consort-HRC 0.0 c
9908 P66 0.0 c
9907 P66 0.0 c
Nadezhnaya 0.0 c
D-16-8-14 0.0 c
Titania 0.0 c
D-16-6-54 0.0 c
9908 P45 0.0 c
Consort-OR 0.0 c
Crusader 0.0 c
z
Means followed by the same letter were not
significantly different using Tukey’s (honestly
significant difference) comparison of means
(P= 0.05).
Table 1. Cronartium ribicola uredinial sori
development on Ribes cultivars based on
observations made of natural infection
occurring in the field at the University of
Minnesota Horticultural Research Center.
Ribes
nigrum
cultivars
The presence of
uredinia on leaves
Sample
size
Yr
2000 2001 2004
Ben Sarek + + + 15
Ben Lomond + + + 15
C2-2-1 + + + 15
D-16-8-14 – – – 15
D-16-6-54 – – – 15
Titania – – – 15
Consort HRC – – – 2
9908 P45 – – – 1
9908 P66 – – – 1
9907 P66 – – – 1
Golubka – – – 2
Nadezhnaya – – – 2
HORTSCIENCE VOL. 43(1) FEBRUARY 2008 201
PLANT PATHOLOGY
effective against C. ribicola more than 50
years after its discovery and first deployment.
The accession Consort acquired at a nur-
sery (‘Consort-MN’) had a similar amount
of uedinial sori development as did the
susceptible European black currant (‘WI-
1’). The other ‘Consort’ accessions from the
USDA-ARS National Clonal Germplasm
Repository (‘Consort-OR’) and University
of Minnesota HRC (‘Consort-HRC’) had no
uredinial development after artificial inocu-
lations. Molecular fingerprinting confirmed
that ‘Consort MN’ differs genetically from
‘Consort-OR’ and ‘Consort-HRC’. This is
likely the result of mixing of clones in a
nursery and mislabeling. However, because
polymorphism was observed at only one of
the six loci tested, it is possible that a
mutation in the plants grown from cuttings
is responsible for their susceptibility. This
somaclonal variation is observed frequently
with other tissue culture-grown plants.
Another possibility that explains the molec-
ular similarity is that ‘Consort-MN’ is a
susceptible offspring of ‘Consort’, perhaps
from a seedling that became established in
a planting of ‘Consort’. Further testing would
be required to verify this. Regardless of the
reason for the variation, the potential impact
for the horticultural industry and the WPBR
pathosystem is significant. In many states,
there are restrictions on planting currants or
gooseberries with exceptions being made for
immune cultivars such as ‘Consort’. If these
clones are mixed up and wrongly sold as
immune, nurseries could be responsible for
the further spread of WPBR and regulations
put into place by state or local authorities to
make sure only immune clones of Ribes are
planted would be ineffective.
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Fig. 1. Photograph of a SYBR green-stained agarose gel showing homogeneity (RJL1) and polymorphism
(RJL2) at two of six Ribes nigrum microsatellite loci tested. Lanes 1 and 8 contain 100-base pair ladder;
lanes 2 and 5 are ‘Consort-OR’; lanes 3 and 6 are ‘Consort-HRC’; and lanes 4 and 7 are ‘Consort-MN’.
202 HORTSCIENCE VOL. 43(1) FEBRUARY 2008
