© Benaki Phytopathological Institute
Evaluation of the virulence of
Sclerotium rolfsii
isolates
3
with a thin soil layer. The experiment was
done as a complete randomized block de-
sign with three replications. There were two
controls for each treatment including pots
inoculated with thirty sterile barley seeds.
After establishment of the fungus in soil, the
germinated peanut seeds were cultured into
pots (one seed per pot) (Toribio
et al
., 1992).
The pots were maintained in greenhouse
conditions at 25±5
o
C (Erkilic
et al.,
2006). The
pots were irrigated based on seedlings need
for prevention of water stress (Flores-Mocte-
zuma
et al
., 2006; Sennoi
et al
., 2010).
Disease symptoms were monitored daily
from one week after peanut seeding, when
the symptoms were observed. At the plants
maturity (about 6 weeks after seeding), all
the plants were uprooted at the same time
and the roots were washed in running tap
water to remove soil particles (Yaqub and
Shahzad, 2005).
Disease severity was assessed by scoring
the plant wilting, yellowing or death, myce-
lia or sclerotia production on the soil surface
or on plant stem, stem area affected (%) and
lesion length. Disease severity index was
calculated for each treatment using these
scores according to the Townsend-Heuberg-
er formula (Erkilic
et al.,
2006) as bellow:
Where,
n: degree of infection according to the scale
(Le
et al
., 2012),
v: number of seedlings per category,
N: total number of seedlings were screened
and
V: highest degree of infection.
Also, shoot wet weight and plant height
were recorded at this stage. The data were
analyzed by the one-way ANOVA followed
by Tukey’s multiple range test for mean
comparison using SAS v. 9.0 software.
Peanut genotypes resistance evaluation
One of the most virulent isolates of
S.
rolfsii
on the tested germplasm was used for
evaluation of the twenty peanut genotypes
resistance in greenhouse conditions as com-
pletely randomized design. The germinated
peanut seeds and the infected barley seeds
were prepared in the same way as men-
tioned in isolates virulence determination
experiment. The germinated peanut seeds
were cultured into pots and two weeks af-
ter seeding, the seedlings were inoculated
with three infected barley seeds (Sennoi
et
al
., 2010). Each cultivar was also inoculated
by three sterile barley seeds as control treat-
ment. The genotype resistance was evaluat-
ed one month after seeding, based on the
scale and characteristics mentioned before
(Le
et al
., 2012).
Table 1.
Sclerotium rolfsii
isolates from different MCGs and host plants.
MCGs
pepper
tomato
squash
bean
sunflower
eggplant
groundnut
Amaranthus
sp.
Euphorbia
sp.
cowpea
Total for all
hosts
MCG1
13
0
0
13
2
0
5
2
0
1
36
MCG2
1
0
0
1
0
0
0
0
0
0
2
MCG3
3
5
1
3
0
2
15
0
2
1
32
MCG4
0
0
0
3
0
1
0
0
0
0
4
MCG5
2
0
0
1
0
0
0
0
0
0
3
MCG6
0
0
0
1
0
0
0
0
0
0
1
Total for all
MCGs
19
5
1
22
2
3
20
2
2
2
78
