ABSTRACT
This study aimed at assessing the inheritance of important agronomic traits in full-sib families of orange-fleshed sweetpotato (OFSP) was conducted at National Root Crops Research Institute, Umudike, Abia State and at, Igbariam, Anambra State. The experiment comprised three phases viz; field evaluation, crosses in crossing block and progeny evaluation. The field evaluation was conducted to assess the magnitude of variability within 47 genotypes and to estimate the yield and nutritional performance which was used to establish a crossing block. The results from root yield at Igbariam showed that K 003 produced the highest root yield (32.60t/ha), followed by Umuspo/3(28.89t/ha), A 079b (26.22t/ha) and Umuspo/1(24.45t/ha). In Umudike, Umuspo/3 produced the highest root yield (29.81t/ha), followed by Delvia (27.88t/ha), Umuspo/1(27.33t/ha) and A 097a (27.19t/ha). With respect to location, Umudike recorded highest root yield (10.09t/ha), compared to that of Igbariam(9.28t/ha). In Igbariam the highest beta carotene, which were 12.35, 12.34, 11.76 and 11.76mg/100g FW were recorded from A 089, A 010a, B 060 and Ex-Oyunga respectively. The results obtained from Umudike showed that highest beta carotene content, which were 11.03 and 11.02 mg/100g FW were recorded from A 080 and A 010a respectively. The result also revealed that in Igbariam, genotype with the highest dry matter content were Delvia(52.16%), A 099 (52.05%), Malawi II (50.76) and Amelia (49.82%). The least dry matter content was recorded from Umuspo/3(17.83). With respect to location, highest dry matter content of 40.23% was obtained in Igbriam compared to Umudike(34.38%). The cluster means showed that cluster I comprised of high yielding genotypes with very high dry matter content, lowest beta carotene content and lowest vitamin A content. The ranking of the 47 OFSP genotypes showed that Delvia had the best overall performance with a Rank Summation Index (RSI) value of 49. The correlation coefficients (r) indicated that root yield had highly positive and significant correlation with total root weight per plant(r = 0.696**, p = 0.01) and total number of root per plant(r = 0.770**, p = 0.01) and highly significant but negatively correlated with pest incidence(r = -0.394**, p = 0.01). Beta carotene had significant and negative correlation with dry matter(r = -0.503**, p = 0.01) and starch (r = -0.364**, p = 0.05). Path coefficient analysis using root yield as dependent variable and others as independent variables showed the highest positive direct effect on root yield (RY) were exhibited by number of roots per plant(NRPP)(0.65) and root weight per plant(RWPP) (0.31). The progeny evaluation was conducted in RCBD involving 59 genotypes (three testers, fourteen lines and forty two crosses) of OFSP. From the results, phenotypic coefficients of variation was higher in magnitude than the genotypic coefficients of variation for all the characters. The magnitude of additive variance (σ2A) was consistently larger than that of dominance variance (σ2D) for all traits studied. All the characters studied had high broad sense heritability (>60%). Lines L5 (A 106 -1) and L13(Solo Abuja -1) were best general combiner for root yield per hectare. Line L7 (A 141 1), L3 (A 089 -1) and L1(A 079b -1) were best general combiners for increased beta carotene content whereas, line, L12(Malinda -2), L11(Malinda -1) and L6(A 106 -2) were best general combiner for dry matter content.
TABLES OF CONTENTS
Title page
i
Declaration ii
Certification
iii
Dedication
iv
Acknowledgement
v
Table of contents
vii
List of tables
xiii
List of figures
xvi
Abstract
xvii
CHAPTER 1 INTRODUCTION
1.1
Sweetpotato 1
1.2 The Aim of the Present Study
4
CHAPTER 2 LITERATURE
REVIEW
2.1
Origin and Distribution of Sweetpotato
5
2.2
Origin of Sweetpotato
5
2.3
Distribution of Sweetpotato
6
2.4 Taxonomy of Sweetpotato
7
2.5
Botany and Morphology of sweetpotato 8
2.6
Growth Habit
9
2.7
Root System
9
2.8
Stem
9
2.9
Leaves
10
2.10
Flowers 10
2. 10.1
Flowering in sweetpotato
11
2.11
Fruit and Seeds
12
2.12
Storage Root
12
2.13
Economic Importance of Sweetpotato
13
2.13.1
Non-food Uses of sweetpotato
14
2.14
Attributes of Preferred Genotypes/Varieties
14
2.15
Agronomic requirements 16
2.15.1
Post-Harvest Handling of sweetpotato
16
2.15.2
Sorting and grading techniques: 17
2.15.3
Packaging and Transportation
17
2.15.4
Storage
17
2.15.5
Processors 17
2.16
Production Constraints of Sweetpotato
18
2.15.1
Biotic and abiotic constraints
18
2.15.2
Inadequate storage facilities
18
2.15.3
High cost of production inputs
18
2.15.4
Sweetpotato pests
18
2.15.5
Sweetpotato diseases and viruses
19
2.15.6
Poor breeding progress for sweetpotato
20
2.15.7
Beta carotene
21
2.16 Dry Matter Content of Orange Fleshed
Sweetpotato (OFSP)
22
2.16.1
Factors affecting dry matter levels
24
2.16.2
Date of planting 24
2.16.3
Soil type
24
2.16.4
Fertilizers 25
2.16.5
Season
25
2.16.6
Harvest 26
2.16.7
Storage
26
2.16.8
Resistance to Losses During Storage 26
2.16.9
Breeding for high dry matter content
27
2.16.10
Selection for high dry matter content
27
2.17
Mendelian Genetics
27
2.18
Quantitative Genetics and Breeding 28
2.19 Heterosis 28
2.20 Incompatibility in Sweetpotato 29
2.18.1
The significance of incompatibility on
sweetpotato improvement 30
2.18.2
The kinds and system of incompatibilities in
sweetpotato 31
2.18.3
Methods to overcome incompatibilities 33
2.18.4
Narrow sense heritability (h2)
34
2.18.5
Negative and zero heritability and its
causes 34
2.21 Estimating
GCA and SCA
35
2.22 Major
Mating Designs in Sweetpotato Breeding
36
2.22.1 The
polycross mating design
36
2.22.2 North
Carolina mating designs
37
2.22.3 Top
cross design
38
2.22.4 Line
x tester design
39
2.22.5 Diallel
cross
40
2.23
Path Analysis
41
CHAPTER 3 MATERIALS AND METHODS
3.1
Experimental Site and Planting Materials
42
3.2
Experimental Design and Phases of The Experiment
44
3.2.1
Phase I (Preliminary field evaluation)
44
3.2.2
Phase II (Establishment of Crossing block and hybridization) 44
3.2.3
Hybridization procedure
45
3.2.4
Phase III (Final field evaluation)
46
3.3
Assessment of Sweetpotato Virus Disease Severity scoring 46
3.4
Flowering Synchronization/Induction
46
3.4.1
Short day treatment
49
3.4.2 Use of trellises to induce flowering
49
3.5
Data Collection
49
3.5.1
(A) Agronomic data
49
3.5.2
(B) Culinary quality of sweetpotato storage roots
50
3.6
Statistical Analysis
51
3.6.1
Estimation of genetic components
52
3.6.2
Combining ability analysis
56
CHAPTER 4 RESULTS AND DISCUSSION
4.1
Soil And Agro-Meteorological Data
57
4.2
Vine Length
60
4.3
Internode Length
62
4.4
Number of Branches
64
4.5
Pest Incidence
66
4.6
Virus Incidence
68
4.7
Days to 50% Flowering, Root Length and Root Girth
70
4.8
Number of Marketable and Unmarketable Roots Per Plant 72
4.9
Weight of Marketable and Un-Marketable Roots Per Plant 74
4.10
Yield of OFSP Genotypes
Evaluated in Umudike and Igbariam In
2015 Planting 76
4.11
Beta Carotene and Vitamin A Content 78
4.12
Dry Matter and Starch
80
4.13
Cluster Analyses
82
4.14
Rank Summation Index
82
4.15 Correlation Analysis
83
4.16
Path Coefficient Analysis
83
4.17
Analysis of Variance for Line x Tester
84
4.17.1
Estimates of general combining ability effects
94 4.17.2 Number of branches at 18WAP
94
4.17.3
Days to 50% flowering
94 4.17.4 Root length
95
4.17.5
Root girth
95
4.17.6
Pest infestation and virus incidence
95
4.17.7
Yield and yield related components 95
4.18
General Combining Ability (GCA) For Culinary Qualities 96
4.20 Estimation of Specific Combining Ability (SCA)
100
4.21 Mean Agronomic Performance for Different
Characters 103
4.21.1
Vine length
103
4.21.2
Internode length
106
4.21.3
Number of branches
106
4.21.4
Pest infestation
107
4.21.5
Virus incidence
116
4.21.6
Days to 50% flowering
116
4.21.7
Root girth
116
4.21.8
Root length
119
4.21.9
Number of marketable roots per plant 119
4.21.10
Weight of marketable roots per plant
119
4.21.11
Total number of roots per plant 122
4.21.12 Total weight of roots per
plant
122
4.21.13
Root yield
122
4.21.14
Starch content (%)
131 4.21.15 Beta carotene (Mg/100gFW) 131
4.21.16 Dry matter content (%)
131
4.22 Mean Performance of Hybrids 136
4.22.1 Vine length
136
4.22.2 Number of branches 136
4.22.3 Pest infestation
137
4.22.4 Virus incidence 137
4.22.5 Days to 50 % flowering
137
4.22.6 Root girth 138
4.22.7 Root length (cm)
138
4.22.8 Number of marketable roots per
plant
138
4.22.9 Weight of marketable roots per
plant
139
4.22.10 Total number of roots per
plant
139
4.22.11 Total weight of roots per
plant
140
4.22.12 Root yield per hectare
140
4.22.13 Starch content (%)
140
4.22.14 Beta carotene content
140
4.22.15 Dry matter content
141
4.23
Estimates of Phenotypic and Genotypic Coefficients of Variation 141
4.23.1 Estimate of σ2g,
σ2e, σ2A and σ2D
142
4.23.2 Broad sense and narrow sense
heritability estimates
143
4.23.3 Estimates of genetic advance
143
4.24 Discussion 145
4.24.1 Mean performance of first
evaluation
145
4.24.2 Cluster analysis 149
4.24.3 Rank summation index analysis
151
4.24.4 Correlation 151
4.24.5 Path Analysis
152
4.24.6
General combining ability effects of parents
153
4.24.7 Estimation of specific combining
ability
155
4.24.8 Mean performance of newly developed
hybrids (genotypes) 157
4.24.9 Genetic estimate
160
CHAPTER 5 CONCLUSION AND RECOMMENDATION
5.1
Conclusion 164
5.2
Recommendation 165
5.3
List of Co-Authored Published Papers on this Research Work 166
References 167
LIST OF TABLES
3.1 Plot number
and names of fifty (50) OFSP genotype
that were used for the experiment 43
3.2 Skeleton
of ANOVA for Line X Tester Design 54
4.1 Meteorological
data of the experimental area at Umudike and Igbariam in 2015, 2016 and
2017 58
4.2 Soil
properties of the two experimental sites in 2015, 2016 and 2017 59
4.3 Vine length (cm) of the 47 OFSP
genotypes evaluated in Umudike and Igbariam in 2015 planting season 61
4.4 Internode length
(cm) of the 47 OFSP genotypes evaluated in Umudike and Igbariam in
2015 planting season 63
4.5 Number of branches (cm) of the 47 OFSP genotypes evaluated in
Umudike and Igbariam in 2015 planting
season. 65
4.6 Influence of
location and OFSP genotypes on pest incidence observed in Umudike and
Igbariam in 2015 planting season. 67
4.7 Influence
of location and OFSP genotypes on virus incidence observed in Umudike and
Igbariam in 2015 planting season. 69
4.8 Characteristics
OFSP genotypes evaluated in Umudike and
Igbariam in 2015 planting 71 season
4.9 Yield characteristics of OFSP
genotypes evaluated in Umudike and
Igbariam in 2015 73 planting season
4.10 Yield characteristics of OFSP genotypes evaluated in Umudike and Igbariam in 2015 75 planting
season.
4.11 Yield characteristics of OFSP
genotypes evaluated in Umudike and
Igbariam in 2015 77 planting season.
4.12 Beta carotene and vitamin A content of the 47 OFSP
genotypes evaluated in Umudike and
Igbariam in 2015 planting season. 79
4.13 Dry matter and starch content of the 47 OFSP genotypes
evaluated in Umudike and
Igbariam in 2015 planting season. 81
4.14 Classification of 47 OFSP according to cluster analysis 86
4.15 Cluster mean values of some
characteristics of 47 OFSP genotypes evaluated in Umudike and Igbariam. 87
4.16 Nutritional and yield characteristics, their ranks and
rank summation index of the 47 OFSP
genotypes evaluated in 2015 in Umudike and Igbariam. 88
4.17 Combined Spearman correlation
coefficient among some agronomic traits in orange fleshed sweetpotato genotypes evaluated in
Umudike and Igbariam. 90
4.18 Line x Tester ANOVA for combining ability for agronomic
and root characters of OFSP
combined across two location 91
4.19 Line x Tester ANOVA for combining ability for pests
damage and root yield characters
of OFSP genotypescombined across two locations 92
4.20 Line x Tester ANOVA for combining ability for root yield
and nutritional qualities of
OFSP genotypes combined across two
locations 93
4.21 Estimates of general combining abilities (GCA) for
parents of some characters in
sweetpotato in combined locations 97
4.22 Combined estimate of general combining ability (GCA) of
parents for yield and yield
related characters in different locations 98
4.23 Combined estimates of general combining ability (GCA) of
parents for culinary qualities
in sweetpotato from different locations 99
4.24 Combined estimates of specific
combining ability (SCA) effect for the hybrids for some 101 characters from
different locations
4.25 Combined estimates of specific combining ability (SCA)
effect for the hybrids for root
yield from different locations 102
4.26 Combined estimates of specific
combining ability (SCA) effect for culinary qualities in 104 hybrids
4.27 Summary of best general combiners and specific combiners
for different characters 105
4.28 Mean values of vine length of OFSP tester, lines and
their progenies at 6, 12 and 18WAP 108
4.29 Mean values of internode length of OFSP tester, lines
and their F1 hybrids at 6, 12 and 110
18WAP
4.30 Mean values of number of
branches of OFSP tester, lines and their F1 hybrids at 6, 12 and 112 18WAP.
4.31 Mean values of pest infestation of OFSP tester, lines
and their F1 hybrids at 6, 12 and 114
18WAP
4.32 Mean values of virus incidence of OFSP testers, lines
and their F1 hybrids at 6, 12 and 117
18WAP
4.33 Mean values of phenological and
root characteristics of OFSP tester, lines and their 120 F1 hybrids
4.34 Mean values of root characteristics of OFSP testers,
lines and their F1 hybrids 123
4.35 Mean values of unmarketable root characteristics of OFSP
testers, lines and their 125
F1 hybrids
4.36 Mean values of root characteristics of OFSP testers,
lines and their F1 hybrids 127
4.37 Mean values of root yield and starch content of OFSP
tester, lines and their F1 hybrids 129
4.38 Mean values of nutritional qualities of root of OFSP
tester, lines and their F1 hybrids 132
4.39 Mean values of nutritional qualities of root of OFSP
tester, lines and their F1 hybrids 134
4.40 Estimate of mean, genetic components of variance,
heritability and genetic advance of
orange -fleshed sweetpotato combined
across locations. 144
LIST OF FIGURES
1 Flower synchronization/induction using short day treatment 47
2
Fastened female and male parent flowers 47
3
The fastened flowers ready for pollinationthe following morning 47
4
Peeling back the corolla to expose stamen 47
5
Exposed anther 47
6
Peeling back the corolla to expose stamen 47
7
Fastened female parent flowers after
hybridization 48
8
Immature sweetpotato capsules with seeds 48
9
Germinating the seeds 48
10 Seedlings
in trays 48
11 Transplanted
seedlings growing out in polyethene bags 48
4.1 Dendrogram of 47 OFSP genotypes
based on agronomic and culinary characters 85
4.2 Path diagram and correlation
coefficient of seven characters. Single headed arrow denotes direct effect on
root yield, double headed arrow denotes the correlation 89
coefficients between traits.
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