Tulbaghia violacea L. II: In vivo antifungal properties towards plant pathogens

In vitro antifungal activity of crude extracts from Tulbaghia violacea against 6 economically important plant pathogenic fungi was previously reported. The in vivo control of Mycosphaerella pinodes, causative of Ascochyta blight, by different concentrations of a crude aerial part extract of T. violacea was subsequently followed qualitatively and quantitatively in terms of lesions that developed over a 6-day period at 20°C on detached pea (Pisum sativum) leaves. Infection by M. pinodes spores was prevented when the extract was applied both before and after inoculation, confirming complete inhibition of spore germination, whereas no phytotoxic effect was observed on the leaves. Additionally, the control of sorghum covered (Sporisorium sorghi) and loose (S. cruentum) kernel smuts by seed treatment with the crude extract was tested under field conditions. Before planting, different sorghum seed lots were inoculated separately with spores from the 2 pathogens at a rate of 0.5% per kg (w/w), followed by treatment with the crude extract, at a concentration of 2.0 mg/mL, 24 h later. A standard fungicide, Thiram (65 W), was applied as a positive control at a rate of 0.25% per kg (v/w). Disease incidence was quantified during harvest and expressed as percentage infected plants. Seed treatment with the extract significantly (P < 0.05) reduced the incidence of both sorghum loose and covered smut diseases, compared favourably with the standard fungicide, and resulted in significant yield increases compared to the untreated control.