Anti-tick activities of extracts of Tulbaghia violacea (Alliaceae) cultivated in hydroponic media amended with entomopathogenic fungi (Hypocreales)

Abstract

Ticks and tick-borne diseases are important limiting factors to the attainment of sustainable animal and human health, affecting livelihood of resource poor farming communities in developing countries. Rhipicephalus appendiculatus and Amblyomma variegatum (Ixodidae) are among the most troubling tick species in Africa. While ticks can be controlled by applying chemical acaricides, these chemicals are quite expensive, especially, for small-scale famers in developing countries. Hence, the quest for alternative tick control over the years have revealed that entomopathogenic fungi (EPF) and plant extracts have huge prospects as sustainable alternatives for tick control. Beauveria bassiana (Hypocreales) is a fungal entomopathogen with the ability to colonize plants endophytically and induce secondary metabolite production in plants, and it has been found to be a potential biological control agent against a wide range of arthropods. Several plant species including plant species belonging to the family Alliaceae possess anti-tick activities (repellent and toxic); therefore, integrating the two strategies by inoculating Tulbaghia violacea with B. bassiana could enhance secondary metabolite contents in extracts obtained from the plant and increase medicinal materials. The primary purpose of the present study was to evaluate the effect of indigenous endophytic entomopathogens inoculation of T. violacea on the plant growth, tissue nutrient contents and secondary metabolites, and anti-tick activities of extracts of T. violacea. The specific objectives were: (i) to carry out a study on the effects of inoculating T. violacea with fungal strains of B. bassiana and Clonostachys rosea on plant growth and tissue nutrient contents in extracts of T. violacea with the view of selecting one of the two fungi for further investigation (ii) to compare secondary metabolite profiles of extracts obtained from plants exposed to fungus (EPF) inoculum and control treatment during cultivation, and (iii) to determine whether exposure of T. violacea to an endophytic fungus (B. bassiana) during cultivation affects the repellent and acaricidal activities of extracts of T. violacea on A. variegatum and R. appendiculatus. The study had two experiments, presented in chapters two and three. In the first experiment, eight weeks old potted seedlings of T. violacea were inoculated separately with B. bassiana (strain SM3) and C. rosea (strain SM8) conidia suspended at concentrations of 1 x 106 conidia mL-1. Plant growth parameters, such as number of leaves, plant height (aerial part), fresh weights of aerial parts, and tissue nutrient contents were assessed. Results indicated that B. bassiana induced higher growth of plants than C. rosea. Inoculation with B. bassiana did not significantly (P ˃ 0.05) influence most of the growth parameters, number of leaves, fresht weight of roots and of fresh weight aerial parts (leaves) of T. violacea assessed in the current study. However, mean plant heights and root lengths were significantly (P < 0.05) higher in favour of B. bassiana treated plants compared to those in C. rosea. Fe contents in the roots (1416.3 ± 305.10 mg/kg) were found to be positively influenced (P < 0.05) by the fungal inoculation. There was a significant difference in roots (P < 0.05) on the uptake of Mn in C. rosea treated plants (243 ± 19 mg/kg) compared to the control group (169 ± 16.37 mg/kg) and B. bassiana treated roots (161.3 ± 14.44 mg/kg). Macro nutrients up take did not differ significantly among treatments on both leaves and roots (P > 0.05).