Mycotoxin production in a carbendazim-resistant strain of fusarium sporotrichioides |
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Authors: | J P F D’Mello A M C Macdonald L Briere |
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Institution: | (1) Crop Science Department, The Scottish Agricultural College, West Mains Road, Edinburgh, UK |
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Abstract: | Mycelial yield and production of three trichothecenes, namely T-2 toxin, diacetoxyscirpenol (DAS) and neosolaniol (NEO) were
compared in control (CS) and carbendazim-resistant strains (RS) ofFusarium sporotrichioides. Each strain was exposed to graded concentrations of carbendazim (0, 1, 2, and 4 μg/ml media) for 2, 5 and 7 days under shake-culture
conditions at an incubation temperature of 25°C. Mycelial yield was significantly (P<0.001) affected by strain, carbendazim
concentration and incubation time. The strain differences in mycelial mass at 2 days (P<0.05) became more pronounced at 5
and 7 days of incubation (P<0.001). However, mycelial growth differences between the two strains were greatest following exposure
to carbendazim, with the effects becoming more divergent with time. Combined results for the three incubation times showed
dose related effects in carbendazim inhibition of T-2 toxin production by CS isolates. In contrast, RS cultures exposed to
the 2 μg/ml addition of carbendazim significantly increased T-2 toxin production (P<0.05 or better). At 1 and 4 μg/ml additions,
T-2 toxin inhibition occurred but the effect was less marked than in the CS series. RS yielded more DAS than CS at 5 days
(P<0.05) and at 7 days (P<0.01) of incubation. The major component of this strain difference arose from the effects of the
2 μg/ml addition of carbendazim (P<0.01). NEO production was also higher in RS than in CS, with the difference becoming progressively
more pronounced from day 5 (P<0.05) to day 7 (P<0.01) of incubation. However, these differences reflected enhanced NEO output
with carbendazim addition of 4 μg/ml (P<0.05) in day 5 extracts and of both 2 μg/ml (P<0.01) and 4 μg/ml additions (P<0.05)
in day 7 samples. Moreover, the ratio of NEO to T-2 toxin production was affected by an interaction involving incubation time,
strain and carbendazim dose (P<0.05 or better). On day 5, this ratio was greater in CS exposed to 2 μg/ml, but at 4 μg/ml,
the ratio was higher in RS. It is concluded that carbendazim resistance induced genuine differences in the synthesis of T-2
toxin and NEO. It is suggested that the strain difference may reside in the conversion of NEO to T-2 toxin which may be sensitive
to fungicide concentration. This would imply that carbendazim resistance induces changes in the terminal rather than initial
phases of trichothecene biosynthesis. |
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