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APPLICATION OF VARIOUS INOCULATION METHODS TO EVALUATE
SUNFLOWER VARIETIES TO SCLEROTINIA SCLEROTIORUM UNDER FIELD
CONDITIONS
R. Ebrahimi A , S. Rahmanpour B , Y. Goosta C , S. Rezaee A
A
Department of Plant Pathology, College of Agriculture and Natural Resources, Science and Research Branch, Islamic Azad
University, Tehran, Iran. Email: ebrahimirouya@gmail.com
B
Seed and Plant Improvement Research Institute (S.P.I.I.), Mahdasht Road, Karaj, Iran.
C
Department of Plant Protection, College of Agriculture, Urmia University, Urmia, Iran.
ABSTRACT. It is necessary to develop cultivars with adequate genetic resistance for reduction of yield losses caused by
Sclerotinia sclerotiorum (Lib.) de Bary. The purpose of this study was to find an effective method of inoculation with S.
sclerotiorum fungus in order to screening and identifying of susceptible and resistant sunflower cultivars under field
evaluations. Three stem inoculation techniques including: 1- mycelium plug, 2- oxalic acid solution and 3 - wheat seeds
infested with Sclerotinia mycelium were employed. Four genotypes including Ghalami (local variety in market), Confeta,
Allstar, and Master were used in this study. Lesion lengths, lesion width, lesion as up and down leading on the stem from
inoculation site were measured after 3, 7, 10, and 14 days of inoculation. The experimental design used was completely
randomized with three replications. The evaluation was repeated three times separately. The analysis of variance showed
significant difference between all employed techniques and incubation days after inoculation. Reaction of cultivars and
employed inoculation techniques were significantly different moreover, mycelial plug demonstrated maximal lesion length
values.
INTRODUCTION
S. sclerotiorum is the soil born pathogen that causes the
disease, resulting wilt, stem rot, or head rot of sunflower.
The fungus has high pathogenicity and attack to more
than 480 plant species (1). This pathogen causes most
economic damages on sunflower worldwide, and has
been subject on disease control in several decades (2).
The chemical control is difficult, expensive, and harmful
for environment. Thus, it is required to develop cultivars
with adequate genetic resistance for yield losses.
Researchers have employed methods to evaluate crops
against the disease under field conditions (3).
Importantly, field screening for disease resistance is still
critical for the development of resistant cultivars (1). The
objective of this study was to find an effective method to
inoculate sunflowers with S. sclerotiorum for screening
and distinguishing resistant and susceptible genotypes.
MATERIALS AND METHODS
The Sclerotinia isolate used in this study was collected as
a single sclerot from North-West Iran. The sunflower
cultivars including Ghalami (local variety in market), and
Confeta, and Alestar and Master were used as
confectionary and oilseed varieties, respectively. Three
stem inoculation techniques: 1- mycelial plug (MP), 2-
oxalic acid solution (OAS) and 3- infested wheat seeds
(IWS), were employed. These methods were used to
compare for resistance evaluation under field conditions.
The treatments were wounded and non-wounded to find
out the effect of wounding on disease progress. Three
days after inoculation, Parafilm of the treated stems was
removed. The lesion lengths were measured after 3, 7, 10,
and 14 days incubation.
RESULTS
Analysis of variance showed significant differences
between the inoculation methods and reaction of
cultivars. Data comparison showed that the MP method is
significantly different from the others and demonstrated
the best infection (lesion length) on sunflower stems
(figure. 1). Furthermore, wounded treatments resulted in
faster progress of the disease in this technique comparing
to others. The largest lesion length on the Alestar cultivar
was established by the MP inoculation technique
meanwhile, Master did not show the disease symptoms
among the genotypes.
lession length (mm)
25
20
15
10
5
0
MP OAS IWS Control
inoculation method
Figure 1. Effect of inoculation methods on lesion length
caused by S. sclerotiorum (MP mycelial plug; OAS
oxalic acid solution; IWS infected wheat seeds).
DISCUSSION
The results we obtained show that MP method for
inoculation has significantly reliable effect on sunflower
genotypes. Interestingly, at last date of measurements, the
susceptible plants demonstrated stem wilt which was not
observed on other used methods. Additionally, hybrid
variety Master as a resistant resource can be used for
sunflower breeding programs.
REFERENCES
1. Motallebi, M., Afshari Azad, H. and Zamani, M.R.
(2008). Polygalacturonase production by Sclerotinia
sclerotiorum, Causal Agent of Canola Stem Rot:
Parameter Optimization Using Taguchi Approach.
World Applied Sciences Journal. 3 (1): 96-101.
2. Gulya, T. (2003). An Inoculation Method for Sclerotinia
Stalk Rot. USDA-ARS Northern Crop Science
Laboratory. Fargo, ND 58102 U.S.A.
3. Bradley, C.A., Henson, R.A., Porter, P.M., LeGare,
D.G., Del Rio, L.E. and Khot, S.D. (2006). Response of
canola cultivars to Sclerotinia sclerotiorum in controlled
and field environments. Plant Disease 90: 215-219.
7th Australasian Soilborne Diseases Symposium 51