| In this study, Beauveria bassiana strains D6-2 and L1-1 were subcultured on medium to compare the differences of germination rate, virulence, toxin production, and virulence related enzyme gene expression among the five generations. The results showed that the F2 generation of both strains had the highest germination rate with 77% and 70%, respectively. The germination rate of F1 generation was lower than that of F2 generation slightly, while it decreased gradually from F2 to F5 generation. Indoor bioassay results against Ostrinia furnacalis (Guenee) showed that LT50 and LT90 of F2 generation decreased compared with that of the F1 generation during subculturing under the concentration of 107 spores/ml, which indicated that its virulence increased, whereas from F2 to F5 generation, the virulence declined.2-Coumaranone was only detected from the F1 generation product of metabolism of both test fungal stains, while it was not detected from F2 to F5 generation, furthermore, the other two kinds of reported toxin were not detected at all in all examples. In order to clarify the impact of subculture on the expression of B. bassiana virulence related enzyme gene, the BbChitl and BbCDEP1 genes expression of both test strains F1-F5 generations, were examined by semi-quantitative RT-PCR, in which the housekeeping gene 18S rRNA was employed as internal control. The results showed that BbChitl and BbCDEP1 genes expressed stably during F1 and F2 generations in two tested strains, while with a decreasing expression level from generation F2 to F5, which gave a positive correlation with the results of virulence against O. furnacalis in the test.
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