Sensitivity of Beauveria bassiana conidia to abiotic factors after successive in vitro subcultures

Abstract

The aim of this study was to evaluate the effect of in vitro successive subcultures of Beauveria bassiana isolates in different nutritional conditions on conidia heat and UV radiation tolerance and on sensitivity to azoxystrobin fungicide. The fungus was initially inoculated in Alphitobius diaperinus (Coleoptera: Tenebrionidae) adults and after its development, the conidia were cultivated in PDA (potato dextrose agar) and MPE (medium to produce Beauveria spp. conidia) originating the first subculture 1st (A) conidia, which were successively multiplied in their media until the 20th cultivation. Conidia taken from the 20th subculture were again inoculated in the insect and after sporulation they were once more multiplied in the media, producing the 1st (B) conidia. For the tests, 1st (A), 10th, 20th and 1st (B) conidia from the CG 152 and Unioeste 40 isolates were used. Successive subcultures and the medium nutritional conditions interfered on the fungus physiology, and the isolates showed different behaviors. The subcultures on PDA showed higher thermotolerance to Unioeste 40 in all subcultures and to CG 152 just after inoculation in the host. B. bassiana was susceptible to UV radiation, and this characteristic was influenced by the subcultures in different media. Both isolates were more tolerant to UV radiation when subcultivated on MPE, while just for the 40 Unioeste this tolerance increased after host inoculation. The B. bassiana sensitivity to azoxystrobin fungicide was affected after successive subcultures in both medium. Conidia originated in MPE were more resistant to fungicide and the host inoculation increased this tolerance. These results show that it is possible to enhance the fungi efficiency to control pests, through the selection of a virulent isolate, and handling their nutritional conditions during cultivation and host inoculation.