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Materials and Methods
Grain samples from fourty-four breeding lines and cultivars of
bread wheat (Triticum aestivum L.) were collected in the
Experimental Fields and farmers' fields near the Institute of Wheat
and Sunflower, Dobroudja, near General Toshevo, Bulgaria. Mycotoxin
concentration in grain (10 g) was determined after extraction with
acetonitrile- water (3:1) and purification by Florisil column and
GC-MS according to the method by Luo et al. (1990). The determination
was made in duplicate for all samples and mean values were
presented.
Results and Discussion
A considerable amount of information is available on the natural
occurrence of Fusarium mycotoxins in infected wheat grain in
the central European countries, Canada, USA, China, Korea and Japan
(Trenholm et al. 1988, Eppley et al. 1984, Ueno et al. 1985, Visconti
et al. 1986, Tanaka and Ueno 1989, Van Egmond 1989, Snijders 1990,
Luo et al. 1992). On the other hand, there has been very little
information in Bulgaria (Yoshizawa 1992). According to these reporta,
DON is distributed worldwide, while NIV is restricted only in
western-Japan, Korea and England (Tanaka and Ueno 1989). In the
present survey we studied 44 samples randomly collected in the region
of Dobroudja and found that more than 80 % of them were contaminated
with DON, while NIV was detected only in one sample (Table
1). A large variability was found in the amount of DON, ranging
from 5 to 187 ng/g dry weight of grain. This level of DON
contamination was similar to that already reported in the central and
south-eastern European countries including Bulgaria (Yoshizawa
1992).
Among several Fusarium species causing fusarium head blight in
wheat, F. graminearum was most frequently distributed in the
humid and moderately humid regions in south-eastern Europe, e. g. in
Rumania and Yugoslavia (Moldovan et al. 1981, Tomasovic and Koric
1991). In the northeastern part of Bulgaria and especially in the
region of Dobroudja, however, F. culmorum has been considered
as the main pathogen. The occurrence of this species varied from 60
to 80 % depending on the year among Fusarium species
recognized in infected wheat grain, followed by F. graminearum
(Petkov unpublished). F. equiseti (Corda) Sacc. and F.
avenaceum (Fr.) Sacc. are considered as semi-important pathogens
infebting wheat spikes in this region (Petkov unpublished). A study
on the mycotoxin productivity of Fusarium species collected
from the infected wheat grain from Dobroudja showed that a majority
of the isolates of F. graminearum and F. culmorum
produced mainly DON and its derivatives on artificial "rice
culture" (Yoshizdwa in prep.). Our result at least shows that DON-
producing strains are more important in epidemics of fusarium head
blight than NIV-producing strains in Bulgaria. It was also noted that
some cultivars that were widely cultivated in the region in the near
past, such as Charodejka, Rusalka and Trakia, showed lower levels of
mycotoxin contamination than the recently developed cultivars
including Yanter and Prostor (Table 1).
Among the latter group, only Prjaspa showed a low level of DON in the
two samples examined. Since DON and related trichothecenes likely
play a role as a virulence factor in the development of fusarium head
blight (Atanassov et al. 1994), the above result might indicate
higher susceptibility of some recent cultivars to this disease.
Our first survey of the natural occurrence of Fusarium
mycotoxins in Bulgaria showed the importance of DON as a
prominent trichothecene mycotoxin in this area. It is emphasized that
this type of survey should be continued at least for some years using
a larger number of samples.
Acknowledgment
This study was supported in part by a grant from Iijima Memorial
Foundation for Promotion of Food Science. Contribution No. 87 from
the Laboratory of Plant Genetics, Faculty of Agriculture, Kobe
University.
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