© Benaki Phytopathological Institute
Evolution in
P. halstedii
3
of Australia.
Plasmopara halstedii
is native
to North America where it was first identi-
fied in 1922 and later reported in France in
1966 (Tourvieille de Labrouhe
et al.,
2000),
when the sunflower crop was developed
and the pathogen was probably introduced
via infected seeds during agricultural trade
(Ioos
et al.,
2007). The major resistance gene
played a very important role in the develop-
ment of sunflower acreages from 1974. Par-
ticularly in Europe and USA all modern va-
rieties carry some major resistance genes.
This resistance allowed the demonstration
of physiological specialization of the patho-
gen, into two races, race 100 in Europe, and
race 300 in North America. Race 710 was in-
troduced into European sunflower cultivated
zones from the USA during the 1980s (Tour-
vieille de Labrouhe
et al.,
2000; Delmotte
et
al.,
2008; Ahmed
et al.,
2012). After recombina-
tion events between races from the USA with
races from Europe occured, a number of new
races emerged in different parts of the world.
Until the present day, 14 races of downy mil-
dew have been identified in Europe (Del-
motte
et al.,
2008; Ahmed
et al.,
2012) and 35
worldwide (Gulya, 2007).
In France, the only race known to occur
was 100 until 1988 when race 710 was dis-
covered. Further races able to overcome the
Pl
loci were discovered over the following
years and were found in distinct geograph-
ical regions with 300, 304, 307, 314, 334,
700, 703, 704, 707, 714, 717, 730 and 770 (Ta-
ble 1). Race 100 was ubiquitous albeit rarely
found due to the use of resistant host culti-
vars. Six of them (304, 307, 314, 334, 704 and
714) have never been documented outside
of France even though sunflower hybrids us-
ing the
Pl6
–
Pl7
genes are grown in other Eu-
ropean countries (Gulya, 2007). This evolu-
tion of
P. halstedii
races seems to be linked
with a quasi-exclusive use of
Pl6
gene since
1990. This gene was overcome by the par-
asite races 704 and 714. Tourvieille de La-
brouhe
et al
. (2010) showed that the
Pl6
clus-
ter on LG8 could be split, with about 0.5 %
recombination, giving lines resistant to rac-
es 330(US), 703, 710 and 730 but susceptible
to race 100 and all the other `3xx` races in-
cluding 300. Moreover, the late use of an-
other gene
Pl5
led to the apparition of the
new race 334 (Delmotte
et al.,
2008; Tour-
vieille de Labrouhe
et al.,
2010; Ahmed
et al.,
Table 1.
Virulence of 15
Plasmopara halstedii
races on sunflower differential lines
Race
Differential lines
D1
Ha-304
a
D2
Rha-265
a
D3
Rha-274
a
D4
PMI3
b
D5
PM-17
a
D6
803-1
c
D7
HAR-4
a
D8
QHP1
b
D9
Ha-335
a
100
S
R
R
R
R
R
R
R
R
300
S
S
R
R
R
R
R
R
R
304
S
S
R
R
R
R
R
R
S
307
S
S
R
R
R
R
S
S
S
314
S
S
R
S
R
R
R
R
S
334
S
S
R
S
S
R
R
R
S
700
S
S
S
R
R
R
R
R
R
710
S
S
S
S
R
R
R
R
R
703
S
S
S
R
R
R
S
S
R
704
S
S
S
R
R
R
R
R
S
707
S
S
S
R
R
R
S
S
S
714
S
S
S
S
R
R
R
R
S
717
S
S
S
S
R
R
S
S
S
730
S
S
S
S
S
R
R
R
R
770
S
S
S
S
S
S
R
R
R
a
USDA genotypes (USA),
b
INRA genotypes (France),
c
IFVC genotypes (Yugoslavia), * S: susceptible,
R: resistant (Tourvieille de Labrouhe
et al.,
2000).
1,2,3,4 6,7,8,9,10,11,12,13,14,15,...34