Insecticidal and antioxidant potential of volatile compounds and nanoparticles from Tulbaghia violacea Harv. inoculated with endophytic fungus Beauveria bassiana (Bals.-Criv.) Vuill

Abstract

This study aimed to investigate the effect of the entomopathogenic fungus Beauveria bassiana on the growth and ability of Tulbaghia violacea to synthesise nanoparticles and volatile compounds. Tulbaghia violacea was inoculated by drenching with different concentrations of B. bassiana conidial concentrations (0 mL−1, 1 × 106 mL−1, 1 × 107, and 1 × 108 conidia mL−1) and the colonization of plant tissue in the different fungal treatments was evaluated. A UV–VIS spectrometer (SPECTROstar nano) was used to determine the presence of nanoparticles while volatile constituents in the plants were analysed with chromatography-mass spectrometry. Polyphenols, alkaloids, flavonoids and antioxidant contents were determined using referenced methods. At least 57 % of plants were successfully colonized at the highest concentration (1 × 108 conidia mL−1). The results showed that treating B. bassiana with T. violacea had no significant effect (P>0.05) on the growth parameters (height, number of leaves, aerial part fresh weight, aerial part dry weight, root fresh weight, and root dry weight) of T. violacea after four weeks post-treatment. The aqueous extracts of T. violacea from both control and B. bassiana-treated plants successfully synthesized gold nanoparticles. Furthermore, the aqueous extracts of plants and gold nanoparticles from both fungus and control treatments were equally toxic to mealybug and induced high mortality. The Gas chromatography–mass spectrometry (GC–MS) results revealed that the number of compounds detected in plants subjected to the different concentrations of fungal inoculum and control did not vary significantly (P>0.05) in leaves and roots. The polyphenol contents in the leaves were not significantly different (P>0.05) among treatments. Similarly, the antioxidant activities were not significantly influenced (P>0.05) by fungal treatment on both leaves and roots. However, T. violacea extracts reduced aqueous gold to gold nanoparticles in both control and fungus-treated plants.