Cladobotryum dendroides, causal agent of cobweb disease
of
Agaricus bisporus, has become increasingly resistant to
methylbenzimidazole carbamate (MBC) fungicides following the extensive
use of
MBC in cultivated mushroom production in Ireland.
Of 38 isolates of C. dendroides obtained from Irish mushroom units,
34 were resistant to carbendazim. Primers based on conserved
regions of the β-tubulin gene were used to amplify and sequence a
portion of
the β-tubulin gene in C. dendroides. A point mutation
was detected at codon 50 in isolates resistant to benzimidazole fungicides,
causing an amino acid substitution from tyrosine to
cysteine. Species-specific PCR primers were designed to amplify the region
of
the β-tubulin gene containing this substitution. The
point mutation removed an Acc I restriction site in the
β-tubulin gene sequence of resistant isolates. Digestion of the PCR
product
with Acc I thus provides a rapid diagnostic test to differentiate
sensitive and resistant isolates of this fungus. EMBL accession number:
Y12256.