Abstract

The inhibitory potential of Hyptis suaveolens leaf and root extracts on fungi associated with postharvest spoilage of cabbage (Brassica oleracea var. capitata) was examined. Collection of diseased cabbage was done in sterile sample bags . Isolation of fungi was carried out by inoculating small sections of diseased tissues excised from the cabbages unto Petri-dishes containing Acidified Potato Dextrose Agar (APDA). The isolated fungi were inoculated in triplicates unto Petri-dishes impregnated with 20, 40, 60, 80 and 100% concentrations of leaf and root extracts. Fungi inoculated on PDA alone and PDA impregnated with extraction solvents, served as controls. Diametric growths of the fungi were measured 24 hourly for 10 days after inoculation. Isolated fungi associated with postharvest spoilage in B. oleracea were Aspergillus niger and Rhizopus nigricans. Ethanol root extracts were highly effective as inhibitors of fungal growth. Ethanol leaf and aqueous root extracts only effectively inhibited A. niger growth. Aqueous leaf extracts of H. suaveolens irrespective of concentration did not inhibit growth of either of the fungal species. Generally, inhibition of fungal species growth decreased based on duration of exposure; effects were in the order: Day 5 effects > day 7 effects > day 10 effects. Ethanol and aqueous leaf and root extracts of H. suaveolens possess fungitoxic properties that might be effective as phytofungicides against fungi responsible for postharvest bio-deterioration of B. oleracea. Better understanding of the bioactive components of these natural extracts and more research into how they can be obtained in large quantities and packaged in a form that can be attractive to farmers is needed.

Key words: Cabbage spoilage, Aspergillus niger, Rhizopus nigricans, growth inhibition, concentration dependent activity, food security, bio-deterioration.