Background: Medicinal plants are used by many ethnic groups as a source of medicine for the treatment of various ailments in both
humans and domestic animals. These plants produce secondary metabolites that have antimicrobial properties, thus screening of
medicinal plants provide another alternative for producing chemical fungicides that are relatively non-toxic and cost-effective.
Materials and methods: Leaf extracts of selected South African plant species (
Bucida buceras
,
Breonadia salicina
,
Harpephyllum caffrum
,
Olinia ventosa
,
Vangueria infausta
and
Xylotheca kraussiana
) were investigated for activity against selected
phytopathogenic fungi (
Aspergillus niger
,
Aspergillus parasiticus
,
Colletotricum gloeosporioides
,
Penicillium janthinellum
,
P. expansum
,
Trichoderma harzianum
and
Fusarium oxysporum
). These plant fungal pathogens causes major economic losses in fruit
industry such as blue rot on nectaries and postharvest disease in citrus. Plant species were selected from 600 evaluated inter alia,
against two animal fungal pathogens (
Candida albicans
and
Cryptococcus neoformans
). Antioxidant activity of the selected plant
extracts were investigated using a qualitative assay (2, 2-diphenyl-1-picrylhydrazyl (DPPH)). Bioautography assay was used to
determine the number of antifungal compounds in plant extracts.
Results: All plant extracts were active against the selected plant phytopathogenic fungi. Moreover,
Bucida buceras had the best
antifungal activity against four of the fungi, with minimum inhibitory concentration (MIC) values as low as 0.02 mg/ml and 0.08
mg/ml against
P. expansum,
P. janthinellum,
T. harzianum and
F. oxysporum. The plant extracts of five plant species did not possess
strong antioxidant activity. However, methanol extract of
X. kraussiana was the most active radical scavenger in the DPPH assay
amongst the six medicinal plants screened. No antifungal compounds were observed in some of the plant extracts with good
antifungal activity as shown in the microdilution assay, indicating possible synergism between the separated metabolites.
Conclusion: The results showed that acetone was the best extractant. Furthermore, our findings also confirm the traditional use of
Breonadia salicina and demonstrate the potential value of developing biopesticides from plants.
