ABSTRACT
Four field experiments were conducted at the Teaching and Research Farm of the Department of
Crop Science, University of Nigeria, Nsukka to: (i) improve the photoperiodic response,
especially in local (late) maturing varieties of Okra; (ii) estimate heterosis and heritability for
improved yield and productivity; (iii) determine combining ability and gene effects of 13
genotypes of okra; (iv) estimate gene effects of quantitative traits; (v) determine inheritance
pattern of qualitative traits for improved fruit production. The experimental materials used were
three local varieties (Ele Ndu, Ele Ogwu, Ele Uhie) collected from local farmers in Nsukka
LGA, Enugu State; and ten improved varieties (LUDU V., Esculentus V, Jokoso, Agwu Early,
TAE 38-Dwarf, V-21 Ivra, Clemson spineless, LD88 V., V.35 and NHE 47-4 V) from the
National Institute for Horticultural Research and Training (NIHORT), Okigwe, Imo State.
General combining ability of the parents and specific combining ability of the hybrids were
estimated using Griffings’ model 1 method 2 in a 5 x 5 diallel crosses. Chi square statistic was
used to test for the inheritance pattern and degree of significance in traits of interest. ‘Ele Uhie’
parent showed significantly (p < 0.05) higher branch length, number of fruits/branch, number of
fruits/plant, number of flowers/plant, plant height at maturity and total fruit yield/ hectare (123.7
cm, 8.31, 29.76, 9.03, 237.66 cm and 32.56 t/ha, respectively) than the other parents. ‘Agwu
early’ parent had lower days to 50% germination, days to flower bud initiation, days to anthesis,
days to 50% flowering, days to first fruiting, days to fruit maturity and plant height at maturity
(4.00, 22.21, 47.13, 48.31, 51.10, 52.28 and 57.8 cm). ‘Ele Uhie’ showed significantly (p < 0.05)
higher 100 seed weight (5.19 g), dry fruit weight (11.46 g), fruit girth (11.10 cm), fruit weight
(34.5 g), number of ridges/pod (11.33) and number of seeds/pod (120.57). The cross ‘UHIE x
LD88’ had significantly (p < 0.05) higher number of branches/plant (7), number of fruits/branch
(8.64), number of fruits/plant (35.63), number of flowers/plant (10.16) and total fruit
yield/hectare (38.25 t/Ha). Higher negative better parent heterosis values were observed in the
cross, ‘UHIE x CLM’ in days to 50% germination (-46.32), days to flower bud initiation (-
49.26), days to anthesis (-46.54), days to 50% flowering (-45.12), days to first fruiting (-45.12)
and days to fruit maturity (-35.05). The cross ‘OGW x LD88’ had higher positive BPH value in
total fruit yield/hectare (161.26). Narrow sense heritability in total fruit yield showed values
above average in all the crosses except ‘AGW x CLM’, ‘AGW x LD88’, ‘CLM x LD88’, ‘OGW
x CLM’ and ‘UHIE x CLM’. ‘Ele Uhie’ was the best general combiner for number of
branches/plant (0.65), number of fruits/branch (2.01), number of fruits/plant (2.37), number of
fruits/stem (3.75) and total fruit yield (9.97). ‘Ele Uhie’ was the best general combiner in days to
flower bud initiation (-7.18), days to anthesis (-7.46), days to 50% flowering (-8.11), days to first
fruiting (-7.46) and days to fruit maturity (-8.43). The cross, ‘UHIE x LD88’ was the best
specific combiner for number of fruits/branch (3.31), number of fruits/branch (0.7414), number
of fruits/plant (9.34), number of flowers/plant (2.53) and total fruit yield (10.26). The gene effect
for total fruit yield showed significant positive additive, dominance and additive x dominance
gene effects occurred in all the crosses with the exception of ‘UHIE x AGW’, ‘UHIE x CLM’
and ‘UHIE x LD88’. The relative proportion of additive gene effect was important for high
heritability estimates recorded. This suggests that its contribution to the inheritance of
earliness is ideal for developing desired hybrids. The medium-long and green with pink patched
fruits predominated in the F2 populations and the observed ratio mostly fitted the expected ratio
of 3:1. The hybrid ‘UHIE x LD88’ with significantly higher yield potential has the potential for
commercial cultivation after further selection.
TABLE OF CONTENTS
Title page i
Certification ii
Dedication iii
Acknowledgement iv
Table of content v
List of Tables viii
List of Plates xv
Abstract xvi
INTRODUCTION 1
LITERATURE REVIEW
Origin and Distribution of okra 3
Growth and Development 3
Fruit and floral biology 4
Reproductive pattern in okra 4
Climatic and soil requirements 5
Economic importance of okra 5
Combining ability and gene action in okra 6
Heterosis in okra 7
Heritability and gene effects studies on okra 8
Hybridization in okra 9
Inter-specific hybridization in okra 9
Inheritance pattern of colour trait in okra 11
Inheritance pattern of spineness in okra 11
Inheritance pattern of fruit shape in okra 12
MATERIALS AND METHODS
Experimental site 13
Land preparation and planting 13
vi
Sources of planting materials 13
Experiment 1 15
Experiment 2 17
Experiment 3 18
Experiment 4 19
Statistical analysis 19
RESULTS
Evaluation of parental accessions 24
Evaluation of F1 hybrids and their parents 27
Estimates of mid parent heterosis of agronomic, yield, yield component traits 31
and fruit traits
Estimates of better parent heterosis of agronomic, yield, yield component
and fruit traits 35
Evaluation of selected parents and F2 segregating hybrids
of okra used for the study 39
Generational means of the agronomic, yield, yield component
and fruit traits of selected parents and their crosses used for the study 43
Estimates of the variance components, broad and narrow sense
heritabilities of the crosses 51
Variance components of general combining ability and specific
combining ability of the okra traits studied 64
Estimates of General Combing Ability (GCA) of the parental accessions
of okra 67
Estimate of the specific combining ability (SCA) of the okra hybrid used
vii
in the study 70
Estimates of gene effects of agronomic, yield and yield component traits
of okra used in the study 73
Estimates of gene effects of fruit traits of okra used in the study 81
Inheritance pattern of qualitative traits of okra studied
Inheritance pattern of fruit shape 86
Inheritance pattern of fruit pubescence 93
Inheritance pattern of fruit colour 100
DISCUSSION 107
Summary and conclusion 117
REFERENCES 120
Appendix
CHAPTER ONE
NTRODUCTION
Okra (Abelmoschus spp.) is one of the most significant vegetable crops in the Malvaceae family
and is very popular in the Indo-Pak subcontinent (Kumar et al., 2010). It belongs to the genus
Abelmoschus and the species esculentus. Okra is an upright annual, herbaceous plant with a
hibiscus-like flower. It is a direct-sown vegetable with duration of 51-68 days for the early
maturing varieties and 70-120 days for the late maturing varieties with partly deep taproot
system. Its stem is semi-woody and sometimes pigmented with a green or reddish tinge of
colour.
According to Martin (1982) and Siemonsma (1982), okra can be broadly classified into two main
varieties, namely: Early Okra [Abelmoschus esculentus (L.) Moench] and Late or West African
Okra [Abelmoschus callei (A. Chev.) Stevils]. Early Okra is similar to exotic Okra cultivars
which are found in several okra growing regions of the world while Late Okra is restricted in
distribution to the most humid parts of West Africa (Singh and Bhatnager, 1975; Martin, 1982;
Siemonsma, 1982). Njoku (1958) coined the names early and late Okra when his studies on
photoperiodism in Nigeria, showed that Early Okra has a Critical Day Length (CDL) of 12.50 h
and so can flower at any time of the year while Late Okra with CDL of 12.25 h can only flower
later in the year, around August-September, when natural day length shortens considerably.
Worldwide production of okra as fruit vegetable is estimated at six million tonnes/year. In West
Africa, it is estimated at 500,000 to 600,000 tonnes/year (Burkil, 1997; Farinde et al., 2007). It is
one of the most important vegetable crops in Nigeria, accounting for 5.5% of the total vegetables
cropped (Sorapong, 2012). Nigeria is the second largest producer of okra in the world with an
estimated 0.72 million tonne produced annually, which represents 15% of total world annual
production (Gulsen et al., 2007). It is a common household vegetable crop, cultivated primarily
for its fresh pods and leaves. It is often called “a perfect villager’s vegetable” because of its rich
source of dietary fibre, minerals, and vitamins; often recommended by nutritionists in cholesterol
controlling and weight reduction programmes (Holser and Bost, 2004; Sanjeet et al., 2010). Its
mucilage is suitable for medicinal and industrial applications (Adetuyi et al., 2012).
2
In crop improvement programme, the success rests upon isolation of valuable gene combinations
as determined in the form of lines with high combining ability, lines which produce good
progenies on crossing being of immense value to the plant breeder (Adiger et al., 2013). Diallel
analysis provides good information on the genetic identity of genotypes as well as being one of
the most powerful tools for characterizing the genetic architecture of plants (Obiadalla-Ali et al.,
2013). Similarly, diallel crosses have been used in genetic research to determinate the inheritance
of a trait among a set of genotypes and to measure combining ability and gene action for
earliness, yield and yield components in Okra (Yan and Kang, 2003).
Okra research, especially in developed countries, has for long been concentrated on early or
conventional okra, with little attention paid to late or West African varieties. Though, they are
photoperiod sensitive with wide variations in days to flowering and fruiting, they also contain
many desirable genes not found in early or conventional Okra (Singh and Bhatnager, 1975;
Martin, 1982; Siemonsma, 1982; Udengwu, 2008). Sensitivity to photoperiodism is a very
important expression of genetic diversity in Okra in West Africa (Udengwu, 2008). The
photoperiodic nature apparently makes it difficult to cultivate the late maturing varieties twice
during a growing season. Early cultivation in February/March often results in excessive
vegetative growth as compared with planting in July/August (Adeniji, 2003).
There is every need to develop early flowering and consequently early maturing genotypes of
okra with improved fruit yield so as to meet the ever increasing demands for the crop. Also, an
understanding and subsequent improvement in the photoperiodic response of okra, especially the
West African varieties is necessary in organizing a systematic breeding programme to improve
yield and associated traits of the crop. Hence, the objectives of the study were:
· To improve the photoperiodic response, especially in local or late maturing varieties of
Okra
· To estimate heterosis and heritability for improved yield and productivity
· To determine combining ability
· To estimate gene effects of quantitative traits
· To determine inheritance pattern of qualitative traits for improved fruit production
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