SILVICULTURAL REQUIREMENTS FOR CONSERVATION OF Plukenetia conophora (MULL ARG) IN SOUTHWESTERN NIGERIA

Abstract

Plukenetia conophora, a liana with economic potentials is threatened by extinction. Ex-situ conservation of the species which requires knowledge of its early growth and vegetative propagation has the potentials to enhance its sustainability. However information on the silvicultural requirements for the early growth of this species is scanty. Hence, in this study, seed germination, seedling growth, macro and micropropagation of Plukenetia conophora in Southwestern Nigeria were investigated. Fruits of P. conophora from Oyo (Ibadan), Ogun (Ijebu-Ode), Osun (Igbajo) and Ondo (Akure) states were collected and used for the study. Using completely randomised design, variations in fruit size, growth of seedlings and biomass production of P. conophora were assessed. Seeds stored for twelve months at room temperature (28oC), in a freezer (-5oC), refrigerator (7oC), dry soil (29oC) and freshly extracted seeds (control) were tested for viability using 1% tetrazolium salt. Effect of seed size: small (<9g/wt), medium (9-11g/wt) and large (12-15g/wt) on germination was investigated. Also, the influence of five watering regimes: submerging in 10 litres of water, watering daily, at 4 and 7 days interval with 250ml/seedling and no watering (control), on seedling growth were assessed. Effects of three organic fertilisers (poultry droppings, cow dung and compost) at 10, 20, 30 and 40g/2kg soil on seedling growth were investigated. Seedlings were decapitated at heights 10, 15 and 20cm above root collar and their coppicing potentials were investigated. Macro propagation of double node cuttings using Indole- Butyric Acid (IBA), Naphthalene Acetic Acid (NAA) and IBA + NAA hormones at 50ppm, 100ppm, 200ppm and their powdery forms at 8g/kg was carried out. Micropropagation using embryo explant on modified Murashige and Skoog (MS) media was studied. Data were analysed using descriptive statistics and ANOVA at p = 0.05. Sources significantly affected the fruit weight and collar diameter while the length of liana was not significantly different. Fruit weight ranged between 96.7±30.2g and 62.4±15.1g. Collar diameter was between 0.9±0.1cm and 0.8±0.2cm and length of liana ranged between 224.8±15.8cm and 182.4±6.7cm. Biomass production ranged between 45.8±6.2g and 33.6±7.1g. Seeds stored at 7oC gave the highest viability of 75% after 30 weeks. Seeds size had no significant effect on early growth. Watering regimes significantly affected growth with daily iii watering producing the longest liana (140.8±7.3cm). Submerging in water and no watering liana wilted after the 8th week. Compost fertilizer at 40g/2kg soil produced the longest liana (242.5±14.1cm) while the control had the shortest (164±8.4cm). Decapitation at height 20cm produced the highest number of coppices (6.0±2.2). Double node cuttings using IBA + NAA in their powdery form produced 90% rooting over the control (no rooting). Embryo culture using MS medium alone produced the highest plantlets (9.0±1.8) while MS + 0.5mg benzyl aminopurine produced none. Viability was maintained in the seed of Plukenetia conophora for 30 weeks when stored at 7oC. Seedling performed best when watered daily. Rooting of double node cuttings was possible using powdery hormone and plantlets of Plukenetia conophora were produced using the embryo as explant.