Materials and Methods
Isolation of Sclerotium cepivorum from garlic fields
During the spring of 2014, the garlic fields in the province
of Hamedan, Iran were surveyed. Diseased plants showing
white rot symptoms were collected and transferred
to the laboratory so that the pathogenic agents could be
isolated. Diseased samples were processed by cutting, removing,
surface sterilising and culturing diseased pieces
of stems and bulbs on Potato Dextrose Agar (PDA) culture
medium. The grown fungal colonies were then purified
and were identified using the standard identification
keys of Barnett and Hunter (1998). Based on the abovementioned
experiments, five isolates of S. cepivorum were
identified.
The pathogenicity test (Koch postulate) was also conducted
and performed to confirm the role of the isolated
fungus in disease occurrence and symptom appearance.
The test was performed on five isolates of S. cepivorum
in a greenhouse experiment with five treatments each with
four replicates. A replicate consisted of a plastic pot containing
2 kg of garlic-field, pasteurised soil pre-inoculated
with S. cepivorum and sown with three garlic seeds (bulbs).
After the appearance of symptoms on garlic plants, the
pathogenic agent was re-isolated from the infected tissues,
identified as described in the above sections, and evaluated
for pathogenicity according to the respective disease
percent induction (Mahdizadehnaraghi et al. 2007). Based
on the above experiments, the most pathogenic isolate of
S. cepivorum was selected to be used for the rest of the study.
Preparation of antagonistic fungal isolates
Isolates of three fungal antagonists including T. flavus,
T. harzianum, and T. asperellum were obtained from the research
laboratory’s microbial collection of beneficial microorganisms,
of the Iranian Research Institute of Plant
Protection. In 2013, these isolates were isolated from the
soil of garlic and potato fields located in the province of
Hamedan, Iran. The antagonistic activities of the isolates
against some fungal pathogens, including S. cepivorum,
were previously evaluated and approved in in vitro conditions
in the above-mentioned laboratory (unpublished
data). The antagonistic fungal isolates used in the study
and their characteristics are presented in table 1.
Development and preparation of bioformulations
Twelve bioformulations were prepared using six isolates
of the above-mentioned fungal antagonists and the
organic and inorganic carriers – rice bran and talc. The
powdery compounds of the carriers were selected based
on their use in previous studies (Kakvan et al. 2013; Samavat
et al. 2014). They were steam-sterilised at 121°C for
30 min, and dried aseptically in glass trays before use.