The effect of the fungus Beauveria bassiana (Hypocreales) on the growth of Tulbaghia violacea and its ability to synthesize nano-particle insecticidal to mealybug

Abstract

Few studies have investigated the effects of biotic factors on the yield and plant production of secondary metabolites. This study aimed to evaluate the effect of the entomopathogenic fungus Beauveria bassiana (Hypocreales) on the growth and ability of Tulbaghia violacea (wild garlic) to synthesise nanoparticles. T. violacea Harv. plants were inoculated by drenching with different concentrations of B. bassiana conidia, concentrations (0 mL-1, 1 x 106 mL-1, 1 x 107, and 1 x 108 conidia mL-1). A UV-VIS spectrometer (SPECTROstar nano) was used to determine the presence of nanoparticles. Conidial colonization of plant tissue in the different fungal treatments was evaluated. Gas chromatography-mass spectrometry was used to analyze volatile constituents in the plants. Each of the polyphenols contents was determined using Folin-Ciocalteu reagent with gallic acid as the standard to measure. Furthermore, antioxidant activities were assessed using (TEAC, DPPH, and FRAP). Up to 57% of plants were successfully colonized at the highest concentration (1 x 108 conidia mL-1). Generally, the results showed that B. bassiana treatment 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) 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 nanoparticle from both fungus and control treatments were equally toxic to mealybug and induced high mortality. The 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 aerial parts 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. In conclusion, although B. bassiana's conidia endophytically colonized T. violacea plants following drenching, this had no significant influence on the plant growth. However, an interesting finding of this study is the ability of T. violacea extracts to reduce aqueous gold to gold nanoparticles in both control and fungus-treated plant.