ABSTRACT
Cassava is a starchy root crop that is among the most important tropical food crops in the world. The plant is endowed with a number of characteristics and exciting potential role in combating food shortage and ensuring food security. Cassava have varying root yield that are also environmental dependent. Field experiments were carried out in 2016/2017 and 2017/2018 planting seasons to assess twenty four (24) cassava genotypes for yield and reaction to diseases across four agro-ecological zones of Nigeria. The trial was laid out in a randomized complete block design with three replications at Umudike, Otobi, Minjibir and Aliero. The main aim of the study was to; identify high yielding cassava genotypes with good adaptation to the different agro-ecological zones, determine yield stability of the cassava genotypes in these environments, assess the responses of the cassava genotypes to major pest and diseases of cassava genotypes and determine inter-relationships of roots yield and associated traits among the cassava genotypes. Analysis of variance (ANOVA) revealed that genotypes had a highly significant effect on most of the growth, pest, diseases, and yield and associated traits. Yield stability results therefore evidently showed that genotype, location, year, genotype x location, genotype x year and location x year were significant (p<.001, and p<0.05) suggesting rational distribution of genotype to agro-ecological zones with different levels of adaptation. COB 5-17 genotype exhibited high performance in root yield (13.5 t/ha) while genotype CW 52A-1 had the least mean root yield (4.50t/ha). Yield and most of the yield components performed higher in 2016/2017 than in 2017/2018 season. Correlation studies and Path Coefficient Analysis showed that fresh shoot weight, number of leaves/plant and number of roots are the most important traits contributing to cassava root yield and therefore demand close attention as selection indices for improvement of cassava genotypes. Some of the genotypes had stable yield across the four environments suggesting that cassava can easily adapt to dry ecological zones. Genotype COB 5-17 was found to be high yielding but exhibited low yield stability across the locations in the GGE biplot ranking. The study confirmed effect of genotype and genotype by environment interaction which clearly indicated Otobi location as a good test environment for cassava research and production. The biplot also showed that genotype G19, G4and G5 were the best performing genotypes while genotypes G17, G4 and G23 were the most stable genotypes across the environments and over the two seasons.
TABLE OF CONTENTS
Title page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Table of Contents vi
List of Tables ix
List of
Figures xi
Abstract xii
CHAPTER 1: INTRODUCTION 1
CHAPTER 2: LITERTURE REVIEW
2.1 Origin and Distribution of Cassava 5
2.2 Classification and Taxonomy of Cassava 5
2.3 Cassava Morphology and Botany 6
2.4 Ecology of Cassava 9
2.5 Major pests and Diseases of Cassava 11
2.5.1 Diseases of cassava 11
2.5.2 Pests of cassava 15
2.6 Production and Yield of Cassava 17
2.6.1 Cassava cultivation 17
2.6.2 Weed management 18
2.6.3 Yield of cassava 19
2.7 Economic Importance of Cassava 21
2.8 Cassava Productivity Constraints 23
2.9 Dry ecology and Cassava Productivity 25
CHAPTER 3: MATERIALS AND METHODS
3.1 Source of Planting Material 27
3.2 Locations of the Experiment 29
3.3 Experimental Design 29
3.4 Agronomic Practices 29
3.5 Data Collection 30
3.5.1 Qualitative traits 30
3.5.2 Quantitative traits 32
3.5.3 Pest and diseases data 34
3.6 Data Analysis 35
CHAPTER 4:
RESULTS AND DISCUSSION
4.1 Soil Physicochemical Properties and
Agro-meteorological Data of the
Experimental Sites 36
4.1.1 Physical properties of the experimental
sites for 2016/2017 36
4.1.2 Agro-meteorological data of the experimental
locations for 2016/2017 38
and 2017/2018 cropping seasons
4.2 Growth Data of Some Selected Cassava
Genotype Evaluated in 4 locations
43
4.2.1 Plant height (m) of the cassava genotypes
across four locations 43
4.2.2 Branch height (m) of the cassava genotype in
the site 45
4.2.3 Stem girth (cm) of the cassava genotypes across
four locations 46
4.2.4 Number of leaves/plant 49
4.2.5 Fresh shoot weight (kg) of the cassava
genotype 51
4.3 Biotic and Abiotic Stress Traits 52
4.3.1 Cassava mosaic diseases (CMD) 52
4.3.2 Cassava bacterial blight (CBB) 55
4.3.3 Cassava anthracnose disease (CAD) 56
4.3.4 Cassava green mite (CGM) 57
4.3.6 Leaf retention 57
4.3.7 Stay green ability of the leaf 59
4.4 Yield and Associated Traits 60
4.4.1 Fresh root yield (t/ha) 60
4.4.2 Number of roots (t/ha) 61
4.4.3 % Dry matter content (DMC) 65
4.4.4 % Starch content 66
4.4.5 Harvest index 67
4.5 Interrelationship Between Yield and Yield
Components 67
4.5.1 Correlation studies 67
4.5.2 Path coefficient analysis 68
4.6 Yield Stability Analysis 71
4.6.1 Summary statistics of yield data 71
4.6.2 Additive main effect and multiplicative
interaction (AMMI) analysis 74
4.6.3 Genotype and genotype by environment (GGE)
biplot model 76
4.7 Discussion 78
CHAPTER 5: CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 83
5.2 Recommendations 83
References 85
LIST OF TABLES
3.1 List of Planting Materials 28
3.2 Description of the
Experimental Sites 29
4.1 Soil Physicochemical
Properties of the Experimental Sites
37
4.2 Agro- Meteorological
data of the Experimental site
39
4.3 Plant height (m) of the
24 cassava genotypes in four locations 44
4.4 Plant height (m) across the four
locations and the planting seasons 45
4.5
Branching
height (m) across 4 sites and over 2 years period 46
4.6 Stem girth (cm) of the cassava genotypes in
four locations 47
4.7 Stem girth (cm) of the cassava genotypes in
two planting seasons
48
4.8 Stem girth (cm) across four
locations and over 2 years period 49
4.9 Number of
leaves/plant of cassava genotypes across four locations 50
4.10 Number of leaves/plant across four locations
and over two years
51
4.11 Fresh shoot weight (kg)/plot across 4 locations and over 2 years 52
4.12 Cassava
mosaic disease severity of the cassava genotypes across four locations 53
4.13 Cassava mosaic disease of the cassava genotypes in two planting
seasons 54
4.14 Cassava
mosaic disease of the cassava genotypes over 2 years and in 4 locations 55
4.15 Cassava bacterial blight of the cassava genotypes over 2 years in 4
locations 55
4.16 Cassava anthracnose disease over two years and in four locations 55
4.17 Cassava green mite of the cassava
genotypes over 2 years and across 4 locations
57
4.18 Leaf retention of the cassava genotypes across
four locations
58
4.19 Leaf retention of the cassava genotypes
over 2 years 59
4.20 Stay green ability of the cassava genotypes in two years period 60
4.21 Fresh root yield t/ha of cassava genotypes
across four locations 62
4.22 Fresh root yield t/ha of cassava genotypes
over two years period 63
4.23 Number of roots/ha of cassava genotypes
over 2 years 64
4.24 Number of roots/ha of the cassava genotypes across 4
locations and over 2 years 65
4.25 % Dry matter content over 2 years and across 4
locations 66
4.26 %
Starch content of the cassava genotypes over 2 years and across 4 locations 66
4.27 Harvest
index of the cassava in four sites and over two years period 67
4.28 Correlation
matrix between root yield and other attributes of 24 cassava genotypes 69
4.29 Path analysis showing direct and
indirect effects of other traits on cassava root yield 70
4.30 Summary statistics describing yield data of 24 cassava genotypes
assessed across eight (8) environments 72
4.31 Anova for AMMI model 74
4.32 AMMI Stability Value
(ASV) of 24 cassava genotypes assessed across
eight (8) environments
75
4.33 First four AMMI selection per
environment 76
LIST OF FIGURES
1 Box-plot
displaying a graphical representation of the summary statistics for yield
data 72
2 Colour chart showing
the correlation among the test environment for yield of 24 cassava genotypes 73
3 GGE biplot for yield
of 24 cassava genotypes in eight (8) environments 77
4 GGE Environment Scaling Biplot
Identifying Mega Environment 78
CHAPTER 1
INTRODUCTION
Cassava,
Manihot esculenta Crantz (Euphorbiaceae) is a starchy root crop that is
among the most important tropical food crops in the world. It is commonly
called cassava in English, Brazilian arrowroot, yuca in Spanish, mandioca in
Portuguese and manioc in French (Dufour, 1988; Westby, 2002). The crop is
heterozygous and diploid plant with 18 pairs of chromosome (2n=36) and out crossed by humans, bees and wasp. It is a woody shrub extensively cultivated as an annual crop in
tropics and subtropical regions for its edible and valuable starchy tuberous
root (Ceballos, 2004). It has the ability to produce economic yields under marginal
production conditions which helps to alleviate problems of hunger and
carbohydrate intake deficiency, thus its importance in terms of food security
in African continent cannot be over-emphasized (Eke-Okoro, 2004).
According
to Sarma et al, (1989), cassava as a
plant is endowed with a number of characteristics and exciting potential role
in combating food shortage and ensuring food security. Some of such potentials include;
ability to perform stably in poor or marginal soils, produce leaves and roots
consumed unlike other staple crops, non-determinate in maturity and can be crop combinations, provides raw material for
industrial/diverse food forms, offers
many different alternative uses as processed food, animal feed, starch, alcohol
bio-fuel for vehicles and flexible in planting, weeding and harvesting. About 80% of the cassava
produced is consumed by humans, while the remaining 20% is used for animal
feeds and agro-industrial purposes. Cassava is the third most important source
of calories in the tropics and sixth most important crop, in terms of global
annual production (FAOSTAT, 2010).The leading countries in the world production
are Nigeria, Thailand, Indonesia, Brazil and Democratic Republic of Congo
(FAOSTAT, 2013). Its production and processing provide employment and income
for the rural poor, especially women and children
According
to Otim-Nape et al (2008),
Productivity in cassava entails average measure of efficiency of production or
having the plant in abundance with relative good and higher yield capacity
which is measured in terms of rate of output (yield) per unit input/given area.
The present demands on cassava for food and industrial raw materials make it
necessary to always provide the farmers with suitable cassava varieties that is
specifically bred for that ecological region to meet the environmental
challenges and the farmer’s need in that locality. Despite the importance of
cassava, its performance is constrained by some biotic and abiotic factors such
as soil, environment, elements of climate and weather, pests/diseases, drought
and host of others (CGIAR, 2000).
The physiological responses of cassava to water
stress and possible mechanisms underlying the crop's tolerance to drought have
been the subject of several studies (Connor and Cock, 1981; Connor and Palta, 1981;
Cock,1985; El-Sharkawy ,1987; Alves and Setter, 2000; Ekanayake,2000;
Ginthinguri, 2000; Olasanmi.et al.,, 2010; Okogbenin et al., 2003; El-Sharkawy, 2002; Lenis et al., 2006).
Philips et al (2006) reported that cassava's ability to produce in marginal
environments and arid region makes it the ideal food security crop in Nigeria.
It has a remarkable ability to tolerate and recover from biotic and abiotic
stresses. Drought adaptation studies in over three decades in cassava have
identified relevant mechanisms which have been explored in conventional
breeding. Drought is a quantitative trait and its multigenic nature makes it
very challenging to effectively manipulate and combine genes in breeding for
rapid genetic gain and selection process (Olasanmi. 2010).
Previous studies (El-Sharkawy, 1993; Okogbenin,
2013), revealed that cassava can be produced adequately in drought conditions
making it the ideal food security crop in marginal environments. Although
cassava can tolerate drought stress, it can be genetically improved to enhance
productivity in such environments. Cassava's huge potential to produce well in
marginal environment has made it a desirable and strategic crop for increasing
food productivity by exploring the vast arable lands in the semi-arid and arid
ecologies in the tropics. The wealth of genetic resources and the genetic
diversity it offers has been deployed in the genetic improvement of cassava for
drought tolerance.
Allem (2002) stated that because of
metabolic efficiency of cassava plant under marginal conditions, it produces
more energy per unit area than other crops under conditions of water stress, in
poor soils and not having specific water-stress sensitive growth stages beyond
storage root initiation. The plant is very productive and can survive under
conditions where other staple food crops, such as grain cereals and legumes,
would rarely produce. El-Sharkawy (1993), reported that cassava shows a high degree
of tolerance to prolonged drought in areas with low and erratic precipitation
of less than 600 mm annually, coupled with dry air, high temperatures (hence,
high potential evapo-transpiration), low fertility soil, high pest and disease
pressure in drought-prone areas of the Northeastern Brazil, the northern coast
of Colombia, the coast of Peru, the Sahelian areas of West Africa, and
drought-prone areas of East and Southern Africa and parts of Thailand.
One of
the challenges facing cassava breeders is to develop cultivars which will remain
productive in poor soils and other unfavorable conditions (Egesi et al., 2013). This research therefore
will help cassava breeders and experts to select cassava genotypes that will
suit different agro-ecological zones in Nigeria. Hence the objectives of this
work are:
1.
to evaluate some cassava
genotypes with a view to identify the phenotypes that are for high yielding and
with good adaptation to different agro-ecological zones.
2.
determine yield stability of
the cassava genotypes in these environments.
3.
assess the reactions of the
cassava genotypes to major pests and diseases of cassava across the different
agro-ecological zones.
4.
determine inter-relationships
of yield and associated traits among the cassava genotypes.
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