INTRODUCTION
The African pear (AP) (Dacryodes edulis (G. Don) HJ Lam) also called bush butter is one of the most important indigenous African Tropical Fruit Trees Species (TFTS). It is a multipurpose tree used as food, medicine, livestock feed and ornamental purposes. The fruit is a source of high quality nutritious, non-greasy natural vegetable oil (44 – 67 %) with possibly numerous industrial uses. The African pear also helps in improving the milk quality of nursing mothers (Okorie et al., 2006). African pear fruit is eaten with maize as butter is eaten with bread. The flowers are useful in apiculture. In recent years there has been a growing awareness of the potentials of African pear as a major source of plant oil; mainly amino acids and triglycerides (Okorie et al., 2006). Despite all these benefits, the AP has not been researched on like other trees because of some problems and constraints such as high flower abortion, propagation constraints, irregular flowering and high post-harvest loses.
In Nigeria, the horticultural fruit trees that have received more research attention are the exotic fruit trees such as citrus (Citrus sinensis cv) and mango (Magnifera indica L). The Few indigenous fruit trees that had been studied include oil palm (Elaeis guineensis Jacq.) and the kola (Cola acuminate (P. Beauv.) Schott & Endl and Cola nitida (Vent) A. Chev.) (Okorie et al., 2000). African pear is little known outside its place of origin (Okorie, 2001).
The long term neglect of TFTS in the area of research, including the African pear (AP) has given rise to a conspicuous lack of information in the horticultural and pomological attributes of the species. This has greatly hampered efforts in their development and optimum utilization. If the environmental and humanitarian dimensions are to be important considerations in future agricultural development agenda, the bridging of the information gap on tropical fruit tree species is a necessity (Okorie et al., 2000). There is a great deal of intra- specific variations in the flowering phenology and fruit set of the AP to warrant the initiation of a selection and improvement programme. But this can only effectively commence when the peculiar abortion problems of the African pear are adequately addressed. This may be achieved through the application of exogenous substances such as auxin, cytokinin, gibberallin, ethylene and abscisic acid.
Knowledge of the AP fruit phenology especially as it relates to flowering and fruit set in the crop is particularly important for the development and improvement of the species.  Phenology is defined as the study of developmental timing in relation to the calendar (Lienth, 1974). This knowledge is of essence because of the following reasons:
Application of hormones, particularly to crops plays a key role in increasing yield. These plant hormones also called phytohormones or exogenous substances are chemicals that help in the growth, development and functioning of plants. They also help in the formation of leaves, flowers, stems, and fruits. Most importantly, some of these hormones help in inducing flowering in plants and preventing fruit abortion (Freemen, 1979). Furthermore, these growth regulators (Urea, Coconut water and gibberelin) carry out vital biochemical reactions that are required for plant survival. These hormones help in determining the sex of flowers, colour of fruits and leaves. They help in the formation of tissues, respiration, energy production and even plant longivity and death.
Citrus and mango growers have been able to improve production and yields by manipulating the phenology and physiology of these crops through the application of hormones (Ali & Lovatt, 1994). It has been reported that sweet oranges may develop two hundred and fifty thousand (250,000) flowers per tree in a bloom season, but only a small amount of these flowers become mature fruits (Domingo et al., 2007). Fruit drop in mango is too high, amounting to about 99% at various stages of growth (Ram, 1983). Such research works is lacking in African indigenous tropical fruit trees species especially African pear.
It has been observed that most African pear plants flower profusely during their flowering season, but majority of these flowers are aborted during fruit-set (Okorie, 2001). In the temperate zone, information on the application of exogenous substances to prevent fruit abortion abounds, while in the tropics, there is scarcity of information on flowering phenology and the effects of application of exogenous substances on flowering and fruit set on African indigenous TFTS. Reduction in floral abortion and fruit drop through the application of exogenous substances may result to significant yield increases in African pear.
The growth and development of plants which comprise germination, seedling growth, flowering and fruiting could be influenced positively or negatively by exogenously applied substances. These substances include growth hormones and other secondary metabolites (Erclishi and Turkai, 1998).
Phenology plays a key role in the survival of any plant. For example, in the manifestation of the physiological aspect of any plant, the timing of such event as flowering is very critical.
How and why does Dacryodes edulis (G. Don) HJ Lam (African pear) differ in their flowering phenology?
How does the variations in flowering phenology affect fruit set within the species?
How does the variations in floral morphology and physiology (e.g. relative proportion of male, female and hermaphrodite flowers) or time of flowering affect phenology and fruit set between and within African pear (AP) fruit types?
What factors are responsible for both high percentage floral abortion and prematurity fruit drop observed within the species?
How can we improve on the percentage flowering of African pear while reducing the high incidence of floral abortion and fruit drop observed within species?
Can flowering and fruit set in African pear be improved upon by the application of exogenous substances, and to what extent?
This work was therefore designed to address the above questions.  The timing of life history events may be largely influenced by evolutionary constraints with selection merely modifying a predetermined underlying pattern as with all other genetically controlled characteristics (Chapman et al.,1999).
Therefore, there is the need to study the phenology of flowering in the African pear and the effects of application of exogenous substances on African pear (Dacryodes edulis (G. Don) HJ Lam) flowering and fruit set. The overall objective is not only to provide basic information required for the improvement of the species but also to improve fruit yields within the species.
The specific objectives of this project are as follows: