DISTRIBUTION, PROPAGATION AND SEEDLING GROWTH OF Pentaclethra macrophylla Benth. AND ITS ALLELOPATHIC EFFECTS ON MAIZE AND OKRA IN SOUTHEASTERN NIGERIA

Abstract

Pentaclethra macrophylla (PM) is an indigenous leguminous tree whose seeds are used as spices in Nigeria. Declining population of PM in the wild and its low domestication has limited its use. The PM occurs in agroforestry and could influence growth of crops such as maize and okra. Previous studies focused on the PM food values, with limited information about its distribution, domestication and allelopathy. Therefore, PM distribution, propagation, seedling growth and allelopathic effects on maize and okra were investigated in Southeastern Nigeria. Floristic survey of PM relative to other trees was conducted in Abia, Ebonyi and Imo States where PM is predominant. Using sampling proportionate to size, one-third of Agricultural Development Programme blocks in Abia (13), Ebonyi (4) and Imo (8) were randomly selected. A 10,000 m2 plot was mapped out on each of three farms and fallows in each block (totaling 150 plots). Tree species growing within each plot were enumerated to determine Relative Importance Value-RIV (%). Stem Girth-SG (cm) of PM at breast height was measured. Seeds of PM (n=200), sourced from wild, were mechanically scarified and soaked in water (27°C) for 0 (control), 6, 12, 24 hours and assessed at 7 Weeks After Sowing (WAS) for germination. Seedling growth of PM on low nutrient 35 kg-pots soils (alluvium, Ferruginous Sandstones (FS) and sandstones) and Nursery Medium (NM) was evaluated for 24 weeks. Dry Weight-DW (g) and Number of Root Nodules (NRN) were determined using standard procedure. Seeds (2/pot) of maize and okra were sown in 12 kg-pots in screenhouse. At 2 WAS, PM Aqueous Leaf Extracts (ALE) at 0 (control), 10, 20, 40 and 80% were applied to the seedlings to evaluate allelopathy. Plant Height-PH (cm) and DW were assessed at 8 WAS. All experiments were laid out in completely randomised design with four replicates. Data were analysed using descriptive statistics and ANOVA at α0.05. The RIV of PM in farms was 10.6(Imo)>7.4(Ebonyi)>4.4(Abia), while on fallows it was 10.6(Imo)>8.7(Abia)>6.0(Ebonyi). Elaeis guineensis and Encephalartos barteri had highest and lowest RIV in Imo (33.7; 0.0)>Abia (31.6; 0.4)>Ebonyi (22.1; 0.0), respectively. Pentaclethra macrophylla stands with SG>150, 50-150 and <50 constituted 9.0, 50.0 and 41.0% of its population, respectively. Germination of seeds at control (76.0±16.7%), 6-h (84.0±16.7%) and 12-h (88.0±26.8%) were similar and significantly higher than 24-h (40.0±17.9%). The DW on alluvium (10.8±2.0), FS (12.6±2.0) and sandstones (11.0±1.1) were similar but significantly higher than NM (8.4±1.3). The NRN on sandstones (17.0±3.4) and FS (21.0±7.8) were similar and significantly higher than alluvium (4.0±1.7) and NM (3.0±2.5). The PH of maize and okra seedlings ranged from 68.9±20.0 and 34.1±14.6 in control to 94.9±18.2 and 52.3±10.9 in 40%-ALE, respectively. Their DW ranged from 6.3±2.5 and 1.2±0.5 in control to 18.6±1.5 and 2.5±1.8 in 40%-ALE, respectively. Pentaclethra macrophylla population was prevalent in Imo State. Scarification and soaking for 12 hours enhanced seed germination. Sandstone and ferruginous sandstone soils stimulated seedling growth and nodulation. Aqueous leaf extract of Pentaclethra macrophylla at 40% encouraged dry matter accumulation and plant height in maize and okra seedlings