Abstract
The efficacy of leaf extracts of basil (Ocimum basilicum), bitter leaf (Vernonia amygdalina), lemon grass (Cymbopogen citratus), neem (Azadirachta indica) and paw-paw (Carica papaya) on major seed-bornefungi: Aspergillus niger, Aspergillus flavus, Botryodiplodia theobromae and Fusarium moniliforme of African yam bean ( Sphenostylis stenocarpa ) seeds, and on seed germination and seedling emergence were studied in vitro and in vivo. All the plants leaf extracts (crude and aqueous) significantly (P . 0.05) reduced the incidence of seed-borne fungi tested and increased seed germination and seedling emergence except lemon grass leaf extract when compared with theuntreated control. Neem extract was the most effective while lemon grass extract was the least. Crude extracts from all the plant leaves tested increased seed germination and seedling emergence of African yam bean seeds and gave significant (P. 0.05) reduction of mycelial growth of all the fungi tested when compared with their aqueous extracts. Leaf extracts of neem, basil, bitter leaf and paw-paw, which are cheap and environmentally safe, are promising for protecting African yam bean seeds against major seed-borne fungi and in the improvement of the crop.
Highlights
A survey of the seed-borne fungi associated with this crop grown in Eastern Nigeria revealed high percentage incidence of Aspergillus niger, Aspergillus flavus, Fusarium moniliforme and Botryodiplodia theobromae (Nwachukwu and Umechuruba, 1991). Umechuruba and Nwachukwu (1994) reported significant reduction in seed germination, seedling emergence and low seed and tuber yield of African yam bean caused by these important seed-borne fungi, as well as reduction in nutritional qualities of the seeds (Umechuruba and Nwachukwu 1997)
Neem leaf extract gave the highest inhibition while the lemon grass extract gave the lowest inhibition
All the leaf extracts gave highest percentage inhibition of A. flavus when compared with the results of other fungi
Summary
Extraction of leaf extracts: The fresh leaves of neem, basil, bitter leaf, paw- paw and lemon grass were carefully washed each alone under tap water and cut into tiny pieces. Aqueous extract was prepared as follows: 1kg whole leaves of each plant was blended separately in one litre of distilled water in a waring blender and sieved through a Buchner funnel to remove debris. To every 15ml of sterile potato dextrose agar medium in Petri dishes, 5ml of either crude or aqueous extract of each plant were added. The efficacy of the leaf extracts was tested using the blotter method and soil mix in buckets. The seeds were soaked in the crude and aqueous leaf extracts separately for one hour and plated on moist blotters as well as in sterilised soil mix in buckets. The untreated seeds were soaked in distilled water for one hour and plated on moist blotters and sterilised soil mix as control. A total of 400 seeds were soaked per extract (crude or aqueous) and 10 seeds plated on blotter per Petri dish. 20 seeds were planted per bucket equidistantly at the depth of 2.0cm and 5 buckets were used per extract treatments
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