Jamaican Ackee (Blighia sapida L.) is a woody perennial, evergreen tree, which belongs to the family Sapindaceae. It was named Blighia sapida in honor of Captain William Bligh who in 1793 took plant samples to Kew Gardens in South London (Lancashire, 2004; Lewis, 1965). This plant is originally from West Africa and was introduced to the West Indies during the 18th century. It is presently found in many Caribbean countries including Barbados, Jamaica, Trinidad, and Haiti. The Jamaican ackee is a tropical to subtropical plant and tends to grow well in average, well-drained soil. It prefers full sunlight and blooms during warm months. It attains ≈6 to 12 m in height, and branches are organized in a spreading formation, which results in a dense crown cover. Leaves are pinnate with six to 10 leaflets, which are obviate in shape and 10 to 15 cm in length. Flowers are small and composed of five petals, and fruits are ovoid and green in color. Fruits also have a leathery skin texture and are borne in clusters, turn red, and split into three or four valves at ripening. Splitting exposes cream yellow arils, a red funicle, and glossy black seeds (Llamas, 2003).
Blighia sapida L. is most popular in Jamaica where it is considered as the national fruit and is consumed in the Jamaican national dish called Ackee and Salt fish. This dish includes a mixture of fruit arils and cod fish. Arils from ripe fruits are also processed in brine, canned, and exported to the United Kingdom (Morton, 1987). The popularity of this evergreen tree is also increasing in Barbados, where it is used in landscaping and fruits are used in several Barbadian dishes.
The fruits of Jamaican ackee are a good source of purified oil and have a high nutritive value and thus make up an important portion of the fatty acid intake of those who consume the fruit. In addition, fruits also contain protein, calcium, potassium, and vitamins (Lancashire, 1995). In Africa, mature arils are eaten raw or in soup and are also fried in oil (Morton, 1987). This plant is used in traditional folk medicine in Brazil where repeated small doses of an aqueous extract of the seed have been used to expel parasites (Morton, 1987). In Cuba, a mixture of ripe arils, sugar, and cinnamon is used to treat dysentery. The bark is used in the preparation of an ointment for pain relief in the Ivory Coast (Morton, 1987).
Trees are most commonly propagated by seeds but seedling plants are not true-to-type and result in fruits of varying size and quality (Crane and Balerdi, 2008). Seeds are affected by desiccation and are considered short-lived. In addition, they can take as long as 2 to 3 months to germinate and as many as 6 years for fruit bearing (Crane and Balerdi, 2008). Other propagation techniques that can be used include budding, grafting, cuttings, and air-layering. The production of seedlings for rootstock is required for budding and grafting and this makes these methods time-consuming and expensive. As a result of the great demand for true-to-type plants, stem cutting and air-layering propagations can be alternative methods for producing true-to-type and inexpensive plants.
Air-layering is the initiation of adventitious root growth on a stem, which is attached to the mother plant until root formation. It is used for a wide variety of plant species, especially those that are difficult to initiate root growth using cuttings (Hartmann et al., 2002). The application of root-promoting substances such as auxins helps in the stimulation of root development and increases uniformity of rooting. This in turn results in the propagating of new plants in a shorter period of time and low cost. IBA is one of the most effective and widely used auxins in vegetative propagation (Blazich, 1988; Dirr and Heuser, 2006; Hartman et al., 2011). It is non-toxic to plants over a wide range of concentrations and is effective in stimulating root growth in a large number of plant species (Hartmann et al., 2002). The objective of this research was to determine the optimum concentration of growth regulator to enhance rooting percentage of the stems that were air-layered.
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