© Benaki Phytopathological Institute
Evaluation of the virulence of
Sclerotium rolfsii
isolates
7
R= resistant with scores of 0-2, MR= mod-
erately resistant with scores 2.1-3, S= sus-
ceptible with scores 3.1-4.99 or HS= highly
susceptible with score 5 (Farooq
et al
., 2011;
Flores-Moctezuma
et al
., 2006). The tested
peanut germplasmwas resistant, moderate-
ly resistant, susceptible and highly suscepti-
ble to 6.41, 12.82, 66.67 and 14.1 percent of
tested isolates, respectively.
The five identified groups in the tested
isolates based on the virulence, overlapped
to some extent with six MCGs identified for
these isolates before (Mehri
et al
., 2013). For
example, MCG4 only included 4 isolates and
the tested peanut germplasm was suscepti-
ble to all of them. The MCG5 only had three
members which caused susceptible or high-
ly susceptible reaction on the tested germ-
plasm. This overlap has not been observed
for all MCGs and some of them included the
isolates with different virulence.
Different peanut genotypes resistance
to one of the most virulent isolates of
S. rolf-
sii
(isolate 53) was determined based on the
scores and criteria mentioned above for iso-
lates virulence evaluation. Variance analy-
sis of the data showed that the genotypes
were significantly different in their resis-
tance to
S. rolfsii
. Considering the calculated
DSI for each genotype (Figure 4), its reaction
to the tested isolate was expressed as R= re-
sistant with scores of 0-2, MR= moderate-
ly resistant with scores 2.1-3, S= susceptible
with scores 3.1-4.99 or HS= highly suscepti-
ble with score 5 (Farooq
et al
., 2011; Flores-
Moctezuma
et al
., 2006).
The genotypes 140 and 183 were resis-
tant to the tested isolate. The genotype 129
was moderately resistant and 137, 138, 193
and 208 were highly susceptible. All the oth-
er genotypes showed susceptible reaction.
The genotypes 140 and 183 had the least
amount of stem lesion length, stem area af-
fection and disease symptom occurrence
Table 2.
Correlation between the measured criteria in the
Sclerotium rolfsii
isolates virulence
evaluation test.
Lesion length
Stem area
affected (%)
Symptom
occurrence (%)
DSI
Plant height
Shoot wet
weight
Lesion length
Pearson
Correlation
1
N
78
Stem area
affected (%)
Pearson
Correlation 0.810**
1
N
78
78
Symptom
occurrence (%)
Pearson
Correlation 0.815** 0.981**
1
N
78
78
78
DSI
Pearson
Correlation 0.831** 0.989** 0.990**
1
N
78
78
78
78
Plant height
Pearson
Correlation -0.730** -0.896** -0.894** -0.906**
1
N
78
78
78
78
78
Shoot wet weight
Pearson
Correlation -0.299** -0.404** -0.371** -0.396** 0.349**
1
N
78
78
78
78
78
78
