Evaluation of biological indices of Beauveria bassiana and Metarhizium anisopliae isolates
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عنوان دوره: سومین کنگره بین المللی حشره شناسی ایران
نویسندگان
Department of Plant Protection, Faculty of Agriculture, Azarbaijan Shahid Madani University, Tabriz, Iran,
چکیده
One of the first steps in the development of entomopathogenic fungi application in microbial control of pests is an appropriate strain selection for this purpose. The virulence of a fungal isolate is related to factors such as spore morphology, germination, growth rate, and the characteristics and the type of organic compounds of the spore surface. In addition, the ability of spores to produce enzymes such as esterase, lipase, protease, N-acetylglucosaminidase and chitinase to initiate the disease are among other important factors in determining the virulence of entomopathogenic fungi. Hereafter, in screening tests of fungal isolates, the evaluation of the mentioned characteristics can be considered as important biological indices for selecting isolates along with the common assessments (LC and LT values). In the present work, the bio-indices of three isolates of Beauveria bassiana (BbSA1, BbSA2 and BbSA75 isolated from East-Azarbaijan province soils) and one isolate of Metarhizium anisopliae (MaCS1, obtained from the Department of Plant Protection, University of Tehran) including vegetative growth, sporulation, germination percentage, hydrophobicity and activity of Pr1 enzyme were evaluated. BbSA2 isolate showed the highest spore production compared to other isolates. All the isolates showed germination percentage greater than 80% and the highest was related to MaCS1 isolate with 100% germination rate. The highest vegetative growth rate was observed in the MaCS1 isolate. In terms of Pr1 enzyme activity, there was no significant difference among the isolates at the probability level of 1%. The highest percentage of hydrophobicity was achieved for the MaCS1 isolate at 91.07%. Finally, by conducting bioassays to determine the correlation between biological indices and virulence rate, it was determined that the hydrophobicity of spore surface was directly related to the virulence of fungi, however, the MaCS1 isolate showed the least amount of LC50 and LT50 among the isolates. High levels of enzyme activity will result in faster pathogenesis in the host, but the activity of Pr1 in these isolates showed lower values (about 0.10 μmol/ml/min in average). According to studies, the enzymatic activity of entomopathogenic fungi depends on spore production under in vivo and in vitro conditions; therefore, spores produced under in vivo conditions reveal higher levels of enzyme activity. This suggests that most of the bio-indices of these fungi are closely related to the host insects in terms of the type of nutrients needed to grow and spore production, and as a result, improvement of this condition will optimize their virulence.
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