ABSTRACT
A research was conducted in Umudike to know the inter and intra family variations that exist between sweetpotato progenies raised from half and full-sib families developed in sweetpotato Research Centre Mozambique (CIP Mozambique). Six hundred and twenty nine (629) progenies raised from both half and full-sib families were used for the experimental layout. The result obtained showed that there were significant differences in the proximate composition analysis carried out on twenty five(25) selected promising progenies in 2015. A highly significant relationship (P<0.05) was observed among the root descriptor traits measured in 2014 between the half and full-sib families. From the result obtained on the half-sib progenies in 2014, the number of marketable roots had a strong positive correlation with the number of unmarketable roots (r=0.402**), marketable roots weight (r=0.316*), total number of roots (r=0.757**) and total root weight (r=0.750**). Also from the result obtained from the full-sib families in 2014, the number of marketable root had a strong positive association with the marketable roots weight (r=0.756) total number of roots (r=0.625**) and total roots weight (r=0.426**). Half-sib progenies like A017 (6.91t/ha), BO17 (7.18t/ha) C029 (4.03t/ha), DO57 (4.88t/ha) all had better performance in yield in tons per hectare. They also had better marketable weight (kg/ha) and marketable root number than other half-sib progenies considered. Also from the result, the progenies of the full-sib families like F010, G007, I017, ZD003, M004, M002, Z15003 where all better than other full-sib families in terms of yield in tons per hectare (t/ha), marketable weight (kg/ha) and marketable root number. High heritability and genetic advance was observed in dry matter, (86%, 150.94) crude protein (96%; 6.96) moisture content (96%; 104.85) and starch content (88%; 122.16) for proximate analysis of the selected sweetpotato progenies in 2015. Also highly significant variance ratios (P<0.05) were observed in Dry matter moisture content and starch content in the proximate analysis of the selected promising genotypes in 2015. From the study it was observed that both the progenies of half and full-sib families have the potential of becoming varieties. This assertion was due to their root descriptor performances.
TABLE OF CONTENTS
Title
page i
Declaration
ii
Certification
iii
Dedication iv
Acknowledgments
v
Table
of contents vi
List
of Tables ix
Abstract x
CHAPTER 1: INTRODUCTION
CHAPTER 2: LITERATURE
REVIEW
2.1 Taxonomy and Origin of Sweetpotato 4
2.2 Biology and Morphology of Sweetpotato 4
2.2.1 Growth habit 5
2.2.2 Storage hoot 5
2.2.3 Stem 6
2.2.4 Leaves and petioles 6
2.3 Economic Importance and Distribution of
Sweetpotato 7
2.4 Cultivation of Sweetpotato 8
2.4.1 Climatic and soil requirements 8
2.4.2 Planting 9
2.4.2.1 Weeding 9
2.4.2.2
Fertilization 10
2.4.2.4 Nitrogen 10
2.4.2.5
Phosphorus 11
2.4.2.6
Potassium 11
2.4.2.7Harvesting
11
2.4.3
Production constraints 12
2.4.4
Sweetpotato virus diseases 14
2.4.5
Symptoms of sweetpotato virus infection 15
2.4.6
Control of sweetpotato virus disease 16
2.4.6.1
Pathogen free planting material 16
2.5
Characterization of Sweetpotato 17
2.5.1
Morphological characterization 18
2.5.2 Molecular characterization 19
2.5.2.1
Simple sequence repeats (SSRs) 20
2.6
Yield Stability 21
2.6.1
Mega – environment identification 21
2.6.2 Stability methods 22
2.7
Genotype by Environment (GxE)
Interaction and Yield Stability 24
2.7.1 Methods of evaluating (GxE) and yield stability 25
2.7.2
GxE interaction and yield stability in
sweetpotato 25
2.7.3
Breeding of sweetpotato 28
2.8
Achievements in Sweetpotato Breeding 30
2.8.1 Breeding for resistance 31
CHAPTER 3: MATERIALS
AND METHODS
3.1
Experimental Site 35
3.2
Soil Sampling and Analysis 35
3.3
Planting Materials 35
3.4
Experimental Design 51
3.4
Agronomic Practices 51
3.5
Data Collection 52
3.6
Method of Data Collection 53
3.7 Data Analysis 54
CHAPTER 4: RESULTS
AND DISCUSSION
4.0 Soil Physico-chemical Properties and
Agrometeorological
Data of Experimental Sites 55
4.1 Variation
(Existing) Among The Progenies of the Half
And Full – Sib Families 58
4.2.1
Root yield of sweetpotato half-sib
progenies in 2014. 58
4.2.2: Root yield of sweetpotato full-sib progenies
in 2014 61
4.2.3: Root performance, virus incidence and
severity of some selected
half-sib
progenies in 2014 63
4.2.4: Root performance, virus incidence and
severity of some selected
full-sib progenies in 2014 65
4.2.5:
Performance of selected half–sib
progenies and check varieties in 2014. 66
4.2.6:
Performance of selected full-sib
progenies and check varieties in 2014 69
4.3:
Variations
Between The Half-and Full-Sib Progenies 71
4.3.1:
Storage root size and number of unmarketable roots. 73
4.3.2: Total number of roots, total roots weight and
yield per hectare of half,
full sib and check varieties. 71
4.3.4:
Correlation analysis of half – sib
progenies in 2014 74
4.3.5:
Correlation analysis of full-sib progenies in 2014 77
4.4 Identification
Of Superior Progenies In the Whole Population 79
4.5 Proximate Composition Of Selected Promising
Progenies
In Both half and Full-Sib Families
88
4.5.1:
Correlation analysis of proximate composition of sweetpotato 89
CHAPTER 5: CONCLUSION
AND RECOMMENDATIONS
96
APPENDIX
REFERENCES
LIST OF TABLES
2.1: Main breeding goals by region after
assessment of constraints and opportunities
in sweetpotato. 34
3.1 List
of genotypes used for the study 37
3.2 List
of materials used for the study 37
4.
1: Soil properties of the experimental
site (Umudike) 56
4.2 Agrometeorological
data of the Experimental sites 2014 and 2015
Cropping Seasons 57
4.3: Mean performance of half-sib progenies in
2014. 60
4.4: Mean
Performance of Selected Full-Sib families in 2014 62
4.5:
Root Performance, virus incidence and
severity of Half-Sib
progenies in 2014
64
4.6: Root
Performance and virus incidence and severity in selected progenies of
Full-Sib Families in
2014 67
4.7: Mean Performance of selected Half – Sib
Progenies and Some check
varieties in 2014 68
4.8: Mean Performance of selected Full – Sib
Progenies and check varieties in
2014 70
4.9:
Half and full-sib families showing
total number of roots, virus incidence
and severity in 2014. 72
4.10 Number
of unmarketable roots and size of storage roots of
selected half- and full-sib progenies in 2014 74
4.11
Total number roots, Total roots weight and yield in tons/hectare of selected
Half, Full –Sib Progenies and Check varieties in 2014
75
4. 12: Correlation coefficient of selected half-sib
progenies in 2014 78
4.13: Correlation Coefficients of selected full-sib
progenies in 2014
80
4.14: Yield of selected promising genotypes and check varieties in 2014
and 2015 cropping seasons
83
4.15:
Grand Mean, Mean Squares and Variance
ratios of the root descriptor
attributes
measured in Selected Promising Progenies in 2014. 85
4.16:
Phenotypic(vp ), Genetic (vg), error
variances, phenotypic coefficient of
variance (PCV), Genotypic Coefficient of
Variance (GCV), Broad
sense heritability (hB) and Genetic
Advance for sweetpotato Root Descriptors
of Seleced Promising genotypes in
2015. 87
17:
Root Descriptor Performance of Selected Promising Sweetpotato Progenies
from
Both half and full-sib families
89
4.18:
Means effect of the proximate
composition of selected promising
progenies in 2015. 91
4.19:
Correlation coefficients of proximate
composition of sweetpotato progenies
in Umudike in 2015 93
4.20:
Grand Mean, Mean squares and variance rations of the attributes measured
in
the proximate analysis of the selected promising genotypes in 2015. 95
4.21:
Phenotypic (VP), genotypic (VG)
and Error (VE) variances, phenotypic
coefficient
of variance (PCV), Genotypic coefficient of variance (GCV),
broad
sense heritability (h2B) and genetic advance for proximate
composition
of selected promising genotypes in 2015
97
CHAPTER
1
INTRODUCTION
Sweetpotato
(Ipomoea batatas L. (Lam) is a
tropical American crop belonging to the family Convolvulaceae. It is a
hexaploid (2n = 6x = 90) (Austin and Human, 1996) and is an important food crop
in tropical and sub-tropical regions of the world. It is a herbaceous
dicotyledonous plant widely grown throughout the tropics and warm temperate
regions of the world (Shukla,1976; Halm, 1977; Burke, 1982; Jane 1982).
Worldwide, sweetpotato is the seventh most important food crop after rice,
wheat, potatoes, maize, yam and cassava (Loebenstein, 2009). It is grown on
about 8.2 million hectares worldwide, yielding about 102 million tons, with an
average yield of about 12.1 tons/ ha (FAOSTAT, 2010). The crop is mainly grown
in developing countries, which account for over 95% of world production. Sweetpotato
has low input requirements, it is easy to cultivate and able to produce under
adverse weather and soil conditions. Sweetpotato root is an excellent source of
vitamin A, the orange fleshed genotypes are noted for their high accumulation
of beta-carotene, the precursor of vitamin A, Vitamin C, vitamin B6,
riboflavin, copper, pantothenic acid and folic acid are also contained in
sweetpotato (Woolfe, 1992). Awareness of sweetpotato as a healthy food crop is
increasing, especially the orange – fleshed sweetpotato which is rich in
pro-vitamin A carotenoids (Woolfe, 1992). It is one of the most important food
crops due to its high yield and nutritive value (Data Franico, 1987). The
utilization of sweetpotato as a food security crop and source of protein, vitamin
A for malnourished children has greatly enhanced the production of the crop in
diverse locations. In sub-Saharan Africa, sweetpotato is the third most
important root crop after cassava (Manihot
esculenta) and yam (Dioscorea spp)
(Well and Muturu, 1994). Nigeria produces about 3.46 million tonnes of sweetpotato
annually (FAOSTAT, 2010). Sweetpotato cultivars have variation in botanical
characteristics and are readily distinguished on the basis of morphological
traits. Most varieties of this crop are self-incompatible, and because of the
obligate outcrossing nature of the crop, have high levels of heterozygosity.
Sweetpotato varieties vary considerably in horticultural and morphological
characteristics with a wide range of yield potential, size, shape, flesh and
skin colour of roots, as well as size, colours and shapes of leaves and
branches. The highest diversity of sweetpotato was found in Central America
based on the use of molecular markers which support the hypothesis that Central
America is the centre of origin of this crop (Zhang et al., 2000). Clonal plants such as sweetpotato produce ramets
(genetically identical offsprings) that have the potential to become
independent of the parent plant. (Hosaka et
al., 2005; Araki et al., 2009).
The use of descriptors in the characterization of sweetpotato is very necessary
because they generally correspond to characteristics whose expressions are easy
to measure, record or evaluate. They therefore permit relatively easy
discrimination between phenotypes. Descriptors related to phenotypic appearance
mostly correspond to the morphological descriptor
of the plant and its architecture (CIAT, 2007). Phenotypic characterization has
been used for identification of duplicates, studies of genetic diversity
patterns and correlation with characters of agronomic importance among other
uses (CIAT, 2007).It is an important
first step in the assessment of sweetpotato and it is done by assessing
variation in vine, leaf, flower and storage root characteristics (CIP et al.,
1991). In addition to morphological and agronomic characters, reaction to
pests, diseases and other stresses have been used to characterize sweetpotato. Sweetpotato
is considered an autohexaploid with hexasomic inheritance (Kumagai et al., 1990; Anwar et al., 2009). The segregation pattern of traits in sweetpotato is
more complex because there are more than two homologous chromosomes that can
pair during meiosis (Kumagai et al.,
2009). Transgene present in just one parent is expected to segregate in a 1:1
ratio if present as a single copy (simplex) or a 4:1 ratio if present as a
double copy (duplex).
Crosses
between commercial sweetpotato cultivars would theoretically produce a high
diversity for many characters. Each F1 progeny has the potential to become a
new variety. Therefore the objectives of this study include.
To
determine the extent of variation existing among the progenies of the half and
full – sib families using root descriptors.
To
determine the extent of variation existing between the half and full-sib
families using root descriptors.
To
identify superior progenies existing in the whole population.
To
determine the proximate composition of selected promising progenies in both
half and full sib- families.
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