Antifungal properties of Agapanthus africanus L. extracts against plant pathogens

Crude extracts of various Agapanthus africanus plant parts were screened in vitro against eight economically important plant pathogenic fungi. Radial mycelial growth was inhibited significantly (P<0.05) in five test organisms, while Pythium ultimum, and to a lesser extent Fusarium oxysporum and Alternaria alternata, showed a degree of tolerance. Subsequently, these crude extracts were tested in vivo in the greenhouse against Mycosphaerella pinodes, the cause of black spot or Ascochyta blight in peas. Fourth internode leaves were removed from 4-week-old pea plants, placed on moist filter paper in Petri dishes and inoculated with a M. pinodes spore suspension 30 min before and after treatment with the extracts. The control of Ascochyta blight by different concentrations of the crude extracts was measured in terms of lesion size over a 6-d period at 20 °C in a growth cabinet. All crude extracts significantly reduced lesion development caused by M. pinodes when leaves were inoculated with spores both before and after treatment with the extracts. Neither of the extracts showed any phytotoxic reaction on the leaves, even at the highest concentration applied. A combined aerial part crude extract of A. africanus was additionally evaluated against sorghum covered (Sporisorium sorghi) and loose (Sporisorium cruentum) kernel smuts under field conditions over two seasons. The extract and a standard fungicide, Thiram that served as a positive control, were applied as seed treatments 1 h after artificially inoculating separate sets of sorghum seed with smut spores. Inoculated, but untreated seeds served as a negative control. The extract reduced the incidence of both loose and covered kernel smuts significantly (P<0.05) and compared favourably with the prescribed fungicide, Thiram. Both treatments resulted in significant yield increases compared to the untreated control. From these results it was concluded that the aerial part crude extract of A. africanus possesses sufficient in vivo antifungal activity to warrant a further investigation.