African pear (Dacryodes edulis (G. Don) HJ Lam) commonly called bush butter is an indigenous multi-purpose but threatened food fruit tree that supports the livelihood of many households in Nigeria. It serves as a food supplement which is normally available during hunger period. Also its medicinal, nutritional and ecological values are highly cherished. . Unfortunately, the species is still mostly collected from the forests and is yet to be developed. This is largely because most of the information necessary for its selection and improvement is presently seriously lacking. Field study trips were therefore conducted in five states of southeastern and south – south Nigeria (Latitude 050 30’N; Longitude 07024’E; Altitude 440m) during the normal flowering, fruiting and ripening period for three (3) consecutive years to evaluate the flowering phenology and effect of application of exogenous growth regulators on African pear. The different types (cultigens) of the species growing in the forests, distant and nearby farms, including homesteads were used. The exogenous growth regulators experiment, the site was D. edulis orchard at IMSU farm. Due to the fact that many tropical fruit trees flower profusely and majority produce many fruits at the onset. Later most of these fruits if not all may be dropped, posing economic problems for the owners. African pear (D. edulis (G. Don) H.J.Lam) is a typical example. The researcher evaluated four growth regulator treatments and calculated their percentage concentration (%). These were Distilled water (control) (T1), 4% Urea (T2), 4%Giberellic acid(T3 ) and 50 % Coconut Water (T4 ). Sixteen mature African pear trees planted seventeen (17) years ago were used for the study and there were four (4) trees in each block. The treatments were applied three (3) weeks before normal flowering time and at two weeks after flowering . Both field and effect of growth regulators characterization studies were made on the variations observed within the species and between the years and location. All were laid out in randomized complete block design. The data were collected and analyzed using analysis of variance and regression/correlation in Stat graphics 16.0 software package. Standard errors and percentages were calculated where appropriate. 450trees and 18,000 fruits were sampled. Parameters collected include time for flowering, fruiting, and fruit set. Important pomological characteristics such as fruit weight, pulp weight, seed weight, fruit length, fruit longitudinal circumference etc. Also collected were floral parameters such as number of inflorescence per flowering branch-let, inflorescence length, number of inflorescence per panicle etc and vegetative parameters like vine length, rachis length, number of leave per ranch etc were also collected. Based on the observed floral attributes, two distinct AP tree species were identified – Female tree, and Male and hermaphrodite tree. Base on pomological attributes, three distinct types of the species were identified, large (big), medium and small. Ten different ripped fruit colors were identified, four unripe fruit colors, time of flowering, fruiting and fruit set varied within location and between locations. Also significant differences were recorded in fruit weight, length, diameter, longitudinal circumference, number of seed, seed weight, and inflorescence length respectively. Significant (p<0.05) differences were observed in mean seed number at Imo state which ranged from 2.46 -9.14, 7.81- and 8.49 – 11.48 in 2013, 2014 and 2015 respectively. The mean number of fruit per inflorescence were statistical (p<0.05) not similar. This ranges from 0.74- 2.73 in 2013, 1.67-3.08 in 2014. Similarly statistical differences were observed in seed weight, leaf length in Imo location, fruit length, seed weight, inflorescence per panicle in Abia State. Also, time of flowering, fruiting and fruit set varies both within and between locations. In terms of flowering and fruiting habit, AP can be seen as an annual since 57% to 77% of the trees are annual while 23% to 43% are biennial and triennial. Fruits drop were very high- 90% to 95% in all the years and locations.
Application of growth regulators significantly enhanced flowering, fruiting and fruit set. The best fruit retention of 76.56 % was obtained by T4 which was however, not significantly (p< 0.05) different from 72.75% fruit set obtained using T3. The control (T1) gave the lowest fruit set of 21.41 % which was however significantly (P < 0.05) different from 66.48% obtained by T2. (NS). Application of 4% Giberellin significantly (P < 0.05) enhances flowering, fruiting and fruit set in African pear (D. edulis). But 50% coconut water was more effective in reducing fruit drop.
Therefore, variations that are of genetic and horticultural interest exist in this multipurpose and endangered tree to warrant a planned selection and improvement program and higher dosage of these growth regulators is encouraged.
TABLE OF CONTENTS
Title Pages i Certification ii
Table of Contents vi
List of Tables xii
List of Figures xviii
List of Plates xxii
1.0 Introduction 1
2.1 Botany and origin of African pear (Dacryodes edulis (G. Don) HJ Lam) 5
2.2 Importance of African pear 6
2.3 Phenology of flowering & fruit set 8
2.3.1 Temporal patterns in leafing phenology 12
126.96.36.199 Community Patterns 12
188.8.131.52 Herbivory as a Selective Force in Leaf Flushing 13
184.108.40.206 Leaf Fall 13
2.3.2 Flowering Phenology 14
220.127.116.11 Community Pattern in Flowering Phenology 14
18.104.22.168 Species Patterns in flowering phenology 15
22.214.171.124 Environmental Cues for Flowering 16
126.96.36.199 Competition for Pollinators and Interference between Species. 16
188.8.131.52 Pre-dispersal Seed Predation 18
184.108.40.206 Inherent Constraints on Flowering 19
2.3.3 Fruiting Phenology 19
220.127.116.11 Selective pressure on timing 19 18.104.22.168 Mast Fruiting 20
22.214.171.124 Keystone Fruit Providers 21
2.4 Floral Physiology 21
2.4.1 Vegetative Growth and Floral Initiation 27
2.4.2 The Role of Plant Growth Regulators (PGRs) 28
2.4.3 The role of Carbohydrates 30
2.5.0 Fruit Physiology 31
2.5.1 Regulation of fruit set and growth. 32
2.6.0 Exogenous Substances of Flowering and Fruit Set 32
3.0 Materials and Methods 37
3.1 Location and experimental conditions 37
3.2.0 EXPERIMENT 1 39
3.2 Flowering Phenology Evaluation and Characterization Studies 39
3.2.1 Flowering Phenology and Field Survey Studies 39
126.96.36.199 Experimental Materials and Characterization Studies for Field Survey 39
188.8.131.52 Data Collection on Flowering Phenology Evaluation
and Characterization Studies for Field Survey 40
184.108.40.206 Statistical Design and Analysis 43
3.3.0 EXPERIMENT 2 46
3.3.1 Evaluation of Effects of Exogenous Substances
Application on African pear Floral Initiation. 46
220.127.116.11 Experimental Materials and Procedure 46
18.104.22.168 Experimental Design and Treatment 46
22.214.171.124 Treatments and Preparation Application 47
126.96.36.199 Data Collection 47
188.8.131.52 Experimental Design and Analysis 47
3.4.0 EXPERIMENT 3 49
3.4.1 Evaluation of Effects of Exogenous Substances
Application on African Pear Fruit Set. 49
184.108.40.206 Experimental Materials and Procedures 49
220.127.116.11 Experimental Design and Data Analyses 51
4.0 Results 52
4.1.0 Experiment 1 52
4.1.1 Flowering Phenology and Characterization Studies 52
18.104.22.168 Phenology of Flowering and Fruiting 52
22.214.171.124 Flower to Anthesis 56
126.96.36.199 Anthesis to Fruit Formation 59
188.8.131.52 Fruiting Mean Intensity 62
184.108.40.206 Fruit Formation to Fruit Set 65
220.127.116.11 Percentage Mean Number of Fruits Formed(dropped)/ Retained (Matured) 68
18.104.22.168 Ripped Fruit Colors 71
22.214.171.124 Unripe Fruit Colors 71
126.96.36.199 Fruiting Habit 75
188.8.131.52 Branching Habit 77
184.108.40.206 Fruit Shape 79
220.127.116.11 Flushing Phenology 81
18.104.22.168.1 Imo state Locations 81
22.214.171.124.2 Rivers State 82
126.96.36.199.3 Abia State 82
188.8.131.52.4 Delta State 83
184.108.40.206.5 Enugu State 83
220.127.116.11 Pomological Characterization Studies 89
18.104.22.168 Location: Imo State 89
22.214.171.124.1 Sub Locations: (Umuduru Egbeaguru, IMSU (Uratta), and Logara. 89
126.96.36.199.1.1 Fruit Weight 89
188.8.131.52.1.2 Pulp weight 90
184.108.40.206.1.3 Pulp Thickness 90
220.127.116.11.1.4 Fruit Longitudinal Circumference 91
18.104.22.168.1.5 Fruit Length 92
22.214.171.124.0 Location: Abia State 101
126.96.36.199.1 Sub Location (Oboro, Alayi and Ngwa). 101
188.8.131.52.1.1 Fruit Weight: 101
184.108.40.206.1.2 Pulp Weight 102
220.127.116.11.1.3 Pulp Thickness 102
18.104.22.168.1.4 Fruit Longitudinal Circumference 103
22.214.171.124.1.5 Fruit Length 104
126.96.36.199.1.6 Number of seed: 105
188.8.131.52.0 Location: Delta state 114
184.108.40.206.1 Sub Locations: (Anwai, Ugbolu and Ogwashiukwu) 114
220.127.116.11.1.1 Fruit weight 114
18.104.22.168.1.1 Pulp weight 115
22.214.171.124.1.2 Pulp Thickness 115
126.96.36.199.1.3 Fruit Longitudinal Circumference 116
188.8.131.52.1.4 Fruit Length 117
184.108.40.206.0 Location: Enugu State 127
220.127.116.11.1 Sub Locations: Nsukka, Oba, and Amachala. 127
18.104.22.168.1.1 Fruit Weight 127
22.214.171.124.1.2 Pulp weight 127
126.96.36.199.1.3 Pulp Thickness 128
188.8.131.52.1.4 Fruit Longitudinal Circumference 129
184.108.40.206.1.5 Fruit Length 130
220.127.116.11.0 Location: Rivers state 140
18.104.22.168.1 Sub Locations: Etche, Elele, and Obiebe. 140
22.214.171.124.1.1 Pulp weight 140
126.96.36.199.1.2 Pulp Thickness 141
188.8.131.52.1.3 Fruit Longitudinal Circumference 142
184.108.40.206.1.4 Fruit Length 14
220.127.116.11 Vegetative Morphology 154
18.104.22.168 Nature of Inflorescence 154
4.2.0 EXPERIMENT 2
4.2.1 Effect of growth regulators on African pear
(Dacryodes edulis (G. Don) HJ Lam) flowering and fruiting. 156
4.3.0 Experiment 3. 158
4.3.1 Effect of Growth Regulators on African pear
(D. edulis (G. Don) HJ Lam) Fruit Set and Fruit Drop 158
5.0 Discussion 164
5.1 Flowering Phenology and evaluation Characterization studies 164
5.2 Evaluation of xogenous Substance Application on Floral Initiation,
Fruiting and Fruit Set Characterization 169
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:
- In an environment, it is necessary to match the life cycle of the crop to the length of the growing season for optimal crop yield. Such information is needed to develop better cropping systems so that high and/or stable productivity can be achieved.
- Introduction of improved genotypes or new crops into regions is largely determined by temperature and phenology (Aitken, 1974).
- Phenology is an essential component in whole crop simulation models which can be applied to specific developmental processes to maximize yields.
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:
- To study and evaluate the phenology of flowering in African pear (Dacryodes edulis (G. Don) HJ Lam).
- To evaluate and assess the intraspecific variations in the flowering phenology and fruit set of the African pear fruit types.
- To evaluate the effects of application of exogenous substances (Gibberellin, urea, and coconut water) on flowering and fruit set in African pear.
- To determine the appropriate exogenous substance application level most favorable for increased flowering and fruit set in African pear species.