The morphology, ecology and fungicidal tolerance of Botrytis cinerea isolates
Field isolates of Botrytis cinerea Pers. from tomato crops gave
rise to two distinct morphological types after successive
single spore isolations; type 1 (T1) characterised by regular,
rapidly growing mycelium and type 2 (T2) characterised by
sparse, often distorted, slow growing mycelium. The frequency
with which isolates produced these morphological types varied
considerably. The reaction to benomyl of both types obtained
remained the same as that of the parent isolate through
successive single spore isolations on fungicide free agar over
Benomyl tolerant field isolates could not be distinguished from
sensitive isolates on the basis of colony morphology.
Examination of 188 isolates of B. cinerea collected from 10
different tomato crops showed that sensitive isolates tended to
be more pathogenic to detached tomato cotyledons and grew
faster in vitro than tolerant isolates. In vitro and in vivo
studies revealed no difference in the competitive ability of
benomyl tolerant and sensitive isolates in mixed culture. In a
study of 17 Lancashire tomato crops all were found to contain
benomyl tolerant strains of B. cinerea although in some cases
benzimidazole fungicides had not been used on the nursery for
up to three years.
Examination of B. cinerea in tomato crops suggested that the
majority of stem lesions arose from infected leaf scars and
were non-aggressive. Side shoot stumps or scars were also
liable to infection and the resulting lesions were more likely
to become aggressive than lesions at leaf scars. Conidia were
considered to be the major source of inoculum although lesions
at leaf scars could take up to 61 days to develop after
deleafing. This delay was attributed to latent infection.
Artificial infection of the petiole with B. cinerea prior to
deleafing greatly reduced the susceptibility of the resulting
leaf scar to subsequent attack by B. cinerea. Extracts from
infected stems were shown to delay the germination of B.
cinerea conidia when compared to extracts from healthy stems.
This inhibition of germination was attributed to a resistance
factor (RF) produced by the fungus or host in response to