© Benaki Phytopathological Institute
Evaluation of the virulence of
Sclerotium rolfsii
isolates
9
with six MCGs identified for these isolates
by Mehri
et al
. (2013). Harlton
et al.
(1995)
found 49 MCG and 12 RFLP-ITS groups in a
worldwide collection of
S. rolfsii
isolates and
they did not find a correlation between MCG
groups and pathogenicity. In our case, there
was also no significant correlation between
the isolates virulence and their geographical
or host plant origin. In a random selection,
not all the identified high virulent isolates
had been isolated from peanut and some,
which were isolated from peanut, were not
virulent on the tested peanut local germ-
plasm. These results were compatible with
the results of research conducted by Flores-
Moctezuma
et al.
(2006) and Le
et al.
(2012).
Regarding the peanut genotypes re-
sistance evaluation, most of the genotypes
were susceptible to the selected most viru-
lent isolate and the resistant reactionwas ob-
served only in few genotypes which showed
no systemic infection symptoms such as yel-
lowing or wilting. The results were similar to
the results reported in other investigations
(Farooq
et al
., 2011; Flores-Moctezuma
et al
.,
2006; Yaqub and Shahzad, 2005).
In this investigation, disease severity was
evaluated using several scoring methods
like the plant wilting, yellowing or death,
mycelia or sclerotia production on the soil
surface or on plant stem, stem area affected
(%) and lesion length, shoot wet weight and
plant height and also percent of the disease
symptom occurrence. We finally concluded
that stem area affection is a very useful crite-
rion for the evaluation of isolates virulence or
genotype resistance and stem lesion length
is of second importance. The two resistant
peanut genotypes to
S. rolfsii
identified in
our study will be useful for the control of the
white rot disease in the peanut fields and
the reduction of the losses through the in-
troduction of the genotypes in Guilan prov-
ince, especially because the genotype 140 is
better than the others based on seed size,
plant height and the canopy.
The authors would like to thank University of
Guilan (Deputy of Research) for its important
technical support and Agriculture and Natural
Resources Research Center of Guilan for prep-
aration of peanut genotypes seeds.
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