Allelopathic Potentials of Selected Sudanese Plants

Abstract

A study was undertaken in the laboratory at the College of Agricultural Studies, Sudan University of Science and Technology . The objective of the investigation was to study the allelopathic potentials and persistence of allelopathic activity of Acacia nilotica (pods), Azadirachta indica (leaves), Boswellia sacra (gum), Calotropis procera (bark), Hibiscus sabdariffa (calyx), Lawsonia inermis (leaves), Nigella sativa (seeds) , Solenostemma argel (leaves), Trigonella foenum-graecum (seeds), and Zingiber officinale (rhizomes). The plant parts were powdered. The allelopathic potential was evaluated using the agar sandwich method. Low temperature melting agar and multi well micro- plates were employed. The agar (3.5 g) was mixed with water (1 L), autoclaved, cooled to 40°C, 5 ml poured into each well, allowed to solidify and the test powder was placed on top. Another layer of ager water mix (5 ml) was added, allowed to solidify and seeds of lettuce or alfalfa were planted. The plates were incubated in the dark at 20±2°C for 72 h. For persistence in soil, plants powder was mixed with soil. The soil was brought to field capacity 28, 21, 14 and 7 days prior to and at termination. A Complete Randomized Design with 5 replicates was adopted in all experiments. Treatments effects were assessed by determining germination and measuring radicle and hypocotyl length. Germination and seedlings growth were expressed as percentage of the respective control. Preliminary experiments showed that powders of all donor plants used at 10 mg/well or more displayed allelopathic effects on the recipient plants. Germination was the least affected (80- 100%), while seedling growth was the most affected. Results from experiments using higher powder levels (25- 150 mg/well) showed that A. nilotica, H. sabdariffa, Z. officinale and B. sacra, reduced lettuce germination by 80- 100%. Germination of alfalfa was less sensitive and was most affected by L. inermis, A. nilotica, and S. argel. The results showed that lettuce and alfalfa seedlings growth was reduced. The radicle was, invariably, more sensitive than the hypocotyl. A. nilotica, C. procera, L. 16 inermis, H. sabdariffa and Z. officinale reduced hypocotyl growth by 75 to 100% and that of the radicle by 80- 100%. The rest of the plants were less effective. A. nilotica, Z. officinale, H. sabdariffa, L. inermis and S. argel reduced alfalfa hypocotyl growth by 10 to 100%, and the radicle growth by 20 to 100%. The rest of the donor plants were less suppressive. Persistence studies in which powder from A. nilotica, H. sabdariffa, L. inermis and S. argel was used indicated that germination and seedlings growth, declined with time and increased with increase of toxins level. Powder (25 mg/g soil) from these plants reduced lettuce and alfalfa germination by 0 to 100%. Residues from L. inermis were the most effective in supersession of germination of lettuce seeds followed in descending order by S. argel and H. sabdariffa. At 150 mg/g soil toxins from S. argel were the most suppressive to lettuce seed germination. However, in case of alfalfa, toxins from S. argel were the most suppressive followed in descending order by H. sabdariffa, A. nilotica and L. inermis. All donor plants were allelopathic to the acceptors. However, the reduction was dependent on the donor and acceptor species and on the concentration of the toxins used. The variability in toxicity suggests the presence of selective and non-selective wide spectrum toxins.