Powdery Mildew Resistance Gene Cluster on Chromosome 7AL in Common Wheat
J. J. Maxwell1, G. Brown-Guedira2, C. Cowger2, D. Marshall2, and J. P. Murphy1
1Dept.
of Crop Science, N. C. State University
2USDA/ARS – Plant Science Research Unit, Raleigh, NC
I NTRODUCTION
• Powdery Mildew caused by Blumeria graminis
f.sp. tritici is an economically important disease
for wheat (Triticum aestivum) growers in
maritime areas
• Genetic resistance is one of the most consistent
and cost effective methods of control
• Single dominant resistance genes tend to be
ephemeral because of the constant virulence
shifts in powdery mildew populations
• Thus, novel resistance genes must be identified
to maintain high levels of control
• To date, two single dominant powdery mildew
resistance genes have been identified on
chromosome 7AL, Pm1 (Hsam et al., 1998) and
Pm 37 (Perugini et al., 2008) in close proximity
to each other
Objectives
• To characterize two North Carolina germplasm
lines for their resistance to powdery mildew
• To identify simple sequence repeat (SSR)
markers linked to the resistance genes to be used
in a marker-assisted selection (MAS) program
Table 1: Differential response of germplasm lines and cultivars after
inoculation with four different powdery mildew isolates from North
Carolina. Each line was scored as resistant (R) or susceptible (S).
Cultivar/
Germplasm line
NC-AG12
NC-AG13
NC-AG11
Axminster
Jagger
Saluda
Bgt Isolate
Pm gene
Yuma E3-14 101a2 W72-27
Unknown R
S
S
R
Unknown R
S
R
R
Pm37
R
R
R
R
Pm1
R
S
S
S
None
S
S
S
S
Pm 3a
S
S
R
R
Linkage Mapping
• Chromosome specific SSR markers were used to assign
the genes in NC-AG12 and NC-AG13 to chromosome 7AL
• The markers mapped in accordance with the wheat
consensus map and also were in close agreement with
Perugini et al. (2008) (Figure 2)
• The NC-AG12 and NC-AG13 genes are postulated to be
distal to Pm37 (Figure 2)
Figure 2: Linkage Maps for Chromosome 7AL and relationships between
NC-AG12, NC-AG13 and NC-AG11. SSR marker and powdery mildew
phenotypic marker names are to the right and Centimorgan estimations to
the left of each linkage group.
RESULTS:
Differential Testing
• Differential powdery mildew reactions among lines indicated
that the resistance genes present in NC-AG12 and NC-AG13
are different from those in NC-AG11 and Axminster
NC-AG12
Xgwm332
NC-AG13
• Differential tests also confirmed that the genes in NC-AG12
and NC-AG13 were different from each other
• The genes are also different than those of the recurrent
parent Saluda which possesses Pm3a located on chromosome
1AS
NC-AG11
1
Xgwm332
Xwmc790
5
Xwmc790
7
Xwmc116
8
Xwmc346
Xwmc116
9
22
Xwmc525
2
MATERIALS and METHODS
• Powdery mildew resistant germplasm lines
NC06BGTAG12 and NC06BGTAG13 (Murphy
et al., 2007) were crossed to the susceptible
cultivar ‘Jagger’.
2
(B)
(A)
(C)
• Two F2:3 populations consisting of 130
individuals in each population were developed,
which are referred to as populations NC-AG12
and NC-AG13.
• Both populations, parental lines, and a
susceptible check ‘Saluda’ were artificially
inoculated with a powdery mildew isolate
‘Yuma’ in the greenhouse. Two pots with five
plants each were tested for each F2:3 line. Each
test was repeated twice.
• If all twenty plants over both tests were resistant
(showed no signs of infection) they were scored
as resistant (R), while if all twenty plants over
both tests were susceptible (showed signs of
infection) they were scored as susceptible (S). If
there was a mixture of both resistant and
susceptible plants within the twenty, the line was
scored as segregating (H).
• DNA for linkage analysis was harvested from
individual F2 plants by the CTAB method. PCR
protocols for linkage analysis with SSR markers
were performed as described by Perugini et al.
(2008).
Xgwm332
Pm37
Xwmc790
13
19
Figure 1: (A) Greenhouse phenotypic screening, small pots are the individual
F2:3 lines and large pots are susceptible spreader Saluda. Differential response
of (B) NC-AG12 (C) Jagger.
1
1
3
Pm – AG13
5
Xwmc525
Xwmc273
Xwmc273
Xwmc525
Pm – AG12
7
7
Xwmc273
Xwmc809
FUTURE WORK
• Further allelism tests between NC-AG12, NC-AG13, and
Axminster are needed to confirm if these genes are linked
or allelic to one another.
• Linkage analyses needs to be conducted between NC-AG11,
NC-AG12 and NC-AG13 to determine are linked or allelic
to one another.
Phenotypic Screening
• The powdery mildew isolate Yuma gave a distinct difference
in reaction between NC-AG12, NCAG13 and Jagger (Table
1, Figure 1)
• Greenhouse screening indicated monogenic control of the
powdery mildew resistance expressed in both NC-AG12 and
NC-AG13 (Table 2)
Table 2: Segregation ratios for NC-AG12 and NC-AG13 populations from
an artificial inoculation in the greenhouse.
F2:3 Population
Number of
individuals per
class (R:H:S)
χ2 P-value for a
1:2:1 (R:H:S)
segregation
NC-AG12
NC-AG13
40 : 65 : 23
23 : 79 : 34
0.1029
0.0693
• These analyses could be used to determine if there is a Pm
gene cluster on 7AL.
Literature Cited
• Hsam, S.L.K., X.Q. Huang, F. Ernst, L. Hartl, and F.J. Zeller. 1998. Chromosomal
location of genes for resistance to powdery mildew in common wheat (Triticum
aestivum L. em Thell.). 5. Alleles at the Pm1 locus. Theor. Appl. Genet. 96:11291134.
• Murphy, J.P., R.A. Navarro, D. Marshall, C. Cowger, T.S. Cox, J.A. Kolmer, S.
Leath, and C.S. Gains. 2007. Registration of NC06BGTAG12, and
NC06BGTAG13 powdery mildew resistant wheat germplasm. Journal of Plant
Registrations 1:75-77.
• Perugini, L. D., J. P. Murphy, D. S. Marshall, G. Brown-Guedira. 2008. Pm37, a
new broadly effective powdery mildew resistance gene from Triticum timopheevii.
Theor. Appl. Genet. (Accepted).