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Abstract
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Beauveria bassiana is a fungus which is widely used as a biological insecticide to control a number of
economically important insect pests. Knowledge of the genetic diversity of the isolates, understanding the
underlying nature of these evolutionary phenomena and finding appropriate and simple screening tools play an
important role in developing effective biocontrol agents. Here, we monitored changes of electrophoretic
karyotype of small molecules of extrachromosomal DNAs, presumably mitochondrial DNA or plasmids in several
individual isolates of B. bassiana during the forced in vitro evolution by continual subculture on artificial media
and then we evaluated these changes on the virulence of the isolates. Through agarose gel electrophoresis of the
small extrachromosomal DNAs molecules, we found that mutations accumulate quickly and obvious changes
take place in extrachromosomal DNAs of some isolates, although this did not always occur. This plasticity in
response to culturing pressure suggests that buffering capacity of fungal genome against mutations is isolate
dependent. Following the forced evolution by sub-culturing, five discriminable electrophoretic karyotype of
extrachromosomal DNAs was observed among isolates. The results showed that some isolates are prone to deep
mutations, but during enforced sub-culturing some others have efficiently conserved genome. These differences
are influensive in screening appropriate isolates for mass production as a keystone in biocontrol program. To
determine the effects of these changes on isolate traits, virulence, germination rate and spore-bound Pr1 activity
were assessed parallel to sub-culturing. The results clearly revealed that parallel to sub-culturing and in
correlation with karyotypic changes, isolates significantly suffered from virulence, germination rate and sporebound
Pr1 activity deficiencies.
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