ABSTRACT
A field trial was conducted at the Research Farms of Michael Okpara University of Agriculture, Umudike, South Eastern Nigeria to evaluate the potential effect of Zingiber officinales rhizomes, Carica papaya seeds and Moringa oleifera leaves on the control of bacterial leaf spot of sweet potato (Ipomoea batatas Lam) in a Randomized Complete Block Design (RCBD) experiment. This study was carried out to isolate, identify and prevent the microorganisms responsible for the leaf spot disease of sweet potato. The experimental design was Randomized Complete Block Design (RCBD) with three replicates, three treatment extracts and three varieties. The sweet potato vines (Umuspo 1, Umuspo 2 and Umuspo 3) were sourced from National Root Crops Research Institute Umudike. Five replicate samples of diseased leaves of sweet potato were obtained randomly from the field. Nutrient agar was used for the isolation and identification of bacteria and fungi respectively. The bacterial populations were estimated after 24hours of incubation while the fungi were observed after 5 days of incubation. The organisms were identified using standard morphological and biochemical tests. The genera of the bacteria isolated and their percentage occurrence include: Pseudomonas (100%), Erwinia (80%), Staphylococcus (40%), Bacillus (20%). Results obtained from the field experiment showed that all the plant parts assessed reduced disease incidence and severity drastically at 5% probability when compared with the untreated control. In this study, extracts of C. papaya seed had the best performance in terms of vine length, number of leaves, stem diameter and number of branches in all the sweet potato varieties, particularly in the result of the combined analysis of extracts used in all the varieties at 4 weeks after treatment. Vine length (144.23cm), number of leaves (270.11), stem diameter (3.54cm) are compared favourably with extracts of Z. officinales on tuber yield at harvest (3.14kg) and M. oleifera in reducing incidence of bacterial leaf spot (16.66%), as well as severity of spots (2.87) (P ≤ 0.05), from the results obtained it means that the extracts of Z. officinales, C. papaya and Moringa oleifera have the potentials to serve as ecofriendly and cheap biopesticides in the management of bacterial leaf spot disease of sweet potato.
TABLE
OF CONTENTS
Title page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Table of contents vi
List of Tables viii
List of Figures ix
Abstract x
CHAPTER 1: INTRODUCTION
1.1
Objectives
of the Study 4
CHAPTER 2: LITERATURE REVIEW
2.1 Diseases of Sweet
Potato 5
2.1.1 Sweet
potato virus diseases 6
2.1.2 Fungal
diseases of sweet potato 7
2.1.2.1 Cercospora leaf spot 8
2.1.2.2 Fusarium wilt or stem rot 9
2.1.3 Bacterial
diseases 10
2.1.3.1 Bacterial stem rot of
sweet potato 10
2.1.3.2 Bacterial wilt 11
2.1.3.3 Bacterial soft rot 12
2.2 Active
Ingredients and Phytochemical Contents of the Plants 13
Part under Investigation
CHAPTER 3: MATERIALS AND METHODS
3.1 Field Trial 16
3.1.1 Study area 16
3.1.2 Field preparation and layout 16
3.2 Source of Planting Materials 16
3.3 Preparation of Extracts from Plant Materials 17
3.3.1 Application of extracts in the field 17
3.3.2 Disease assessment 17
3.3.3 Assessment of growth and yield parameters 18
3.4 Laboratory Experiment 19
3.5 Identification of Pathogens 20
3.6 Statistical Analysis 22
CHAPTER 4: RESULTS AND DISCUSSION
4.1 Variety One (Umuspo 1) 23
4.1.1. Effect of plant extracts on the growth
parameters 2 23
weeks after treatment
(2 WAT)
4.1.2. Effect of plant extracts on disease
incidence and severity, 26
growth and yield
parameters of sweet potato 4 weeks after
treatment (WAT).
4.1.3. Effect of plant extracts on disease
incidence, severity and 29
growth parameters 6
weeks after treatment (6WAT) in the field.
4.1.4. Effect of plant extract on disease
incidence, severity, growth 31
and yield parameters
8 weeks after treatment (WAT)
4.2 Variety Two (Umuspo 2) 34
4.2.1. Effect of plant extracts on the growth
parameters, 34
2 weeks after
treatment (WAT)
4.2.2: Effect of plant extracts on disease
incidence and severity, 36
growth and yield
parameters 4 weeks after treatment (4 WAT)
4.2.3. Effect of plant extracts on disease
incidence, severity and growth 39
parameters 6 weeks
after treatment (6 WAT) in the field
4.2.4. Effect of plant extracts on disease
incidence and severity, 42
growth and yield
parameters 8 weeks after treatment (WAT)
4.3 Variety Three (Umuspo 3) 45
4.3.1 Effect of plant extracts on growth
parameters 2 weeks after 45
treatment (WAT)
4.3.2. Effect of plant extracts on disease
incidence and severity, 47
growth and yield
parameters 4 weeks after treatment (WAT)
4.3.3. Effect of plant extracts on disease
incidence and severity, 50
growth and yield
parameters 6 weeks after treatment (6 WAT)
4.3.4. Effect of plant extracts on disease
incidence and severity, 53
growth and yield
parameters 8 weeks after treatment (WAT)
4.4 Combined Analysis of the
Extracts used in all the Varieties 56
4.4.1 Effect of plant extracts on growth and
yield parameters 2 56
weeks after treatment
(WAT).
4.4.2: Effect of plant extracts on disease
incidence and severity, 59
growth and yield
parameters 4 weeks after treatment (WAT).
4.4.3: Effect of plant extracts on disease
incidence and severity, 62
growth and yield
parameters 6 weeks after treatment
4.4.4: Effect of plant extracts on disease
incidence and severity, 64
growth and yield
parameters 8 weeks after treatment
4.5 Laboratory 67
4.5.1 Characterization of leaf
spot pathogen in the laboratory 67
CHAPTER 5: DISCUSSION, CONCLUSION AND RECOMMENDATION
5.1 Discussion 70
5.2 Conclusion 73
5.3 Recommendations 74
References 76
Appendices
LIST
OF TABLES
4.1.1: Effect of Plant
Extracts on Growth Parameters 2 Weeks after 25
Treatment (WAT)
4.1.2: Effect of Plant
Extracts on Disease Incidence, Severity and 28
Growth Parameters 4 Weeks after Treatment
4.1.3: Effect of Plant
Extracts on Disease Incidence, Severity and Growth 30
Parameter 6 Weeks after Treatment
4.1.4: Effect of Extracts on
Disease Incidence, Severity and Growth 33
Parameters 8 Weeks after Treatment
4.2.1: Effect of Plant
Extracts on Growth Parameters 2 Weeks 35
after Treatment (WAT)
4.2.2: Effect of Plant
Extracts on Disease Incidence and Severity, 38
Growth and yield Parameters 4 Weeks after Treatment
(WAT)
4.2.3: Effect of Plant
Extracts on Disease Incidence, Severity and 41
Growth Parameters 6 Weeks after Treatment (WAT)
4.2.4: Effect of Plant
Extracts on Disease Incidence and Severity, 44
Growth and yield Parameters 8 Weeks after Treatment
(WAT)
4.3.1: Effect of Plant
Extracts on Growth Parameters 2 Weeks 46
after Treatment (WAT)
4.3.2: Effect of Plant
Extracts on Disease Incidence, and Severity, 49
Growth and yield Parameters 4 Weeks after Treatment
(WAT)
4.3.3: Effect of Plant
Extracts on Disease Incidence and Severity, 52
Growth and Yield Parameters 6 Weeks after Treatment
(WAT)
4.3.4: Effect of Plant
Extracts on Disease Incidence and Severity, 55
Growth and Yield Parameters 8 Weeks after Treatment
(WAT)
4.4.1:
Effect of Plant Extracts on Growth
Parameters 2 Weeks after Treatment 58
4.4.2: Effect of Plant
Extracts on Disease Incidence and Severity, Growth 61
and Yield Parameters 4 Weeks after Treatment (WAT)
4.4.3: Effect of Plant
Extracts on Disease Incidence and Severity, 63
Growth and Yield Parameters 6 Weeks after Treatment
(WAT)
4.4.4: Effect of Plant
Extracts on Disease Incidence, Severity and Growth 66
Parameters 8 Weeks after Treatment
4.5.1:
Occurrence of Bacteria Isolates in
Sweet Potato Leaf Samples 68
4.5.2: Morphological and
Biochemical Characteristics of the Bacteria Isolates 69
LIST
OF FIGURES
1: Sweet
potato field 89
2: The
plant extracts 89
3: Disease
specimen 89
4: Pure
culture of bacteria isolates 89
CHAPTER 1
INTRODUCTION
Sweet potato (Ipomoea
batatas (L) Lam) is a tropical and creepy herbaceous crop that is of the Convolvulaceae
family and belongs
to the Ipomoea genus (Woolfe, 1992). The family consists of 45 genera
and 1,000 species, out of which only Ipomoea batatas remains an economic
importance to man and animals (Woolfe, 1992). It is known to be globally vital,
adaptable and under-explored food crop (International Potato Centre (CIP),
1999). Annual production of the sweet potato is measured to be about 133
million tonnes annually, In the global food crop fresh weight basis, the third
world countries have sweet potato as the most vital food crop after other
cereals and cassava with a ranking of
fifth (CIP, 1999). Average harvest in numerous countries is well under the
normal yield of 15 tonnes per hectare for third world countries in general,
which is well below the crop’s potential. In Africa, Nigeria is second largest
producer of sweet potato after Uganda with 2,600,000 metric tonnes annually
(National Root Crops Research Institute, 2009).
In Nigeria, the
awareness of sweet potato farming have broadened to all nooks and crannies of
the ecological zones within ten years (NRCRI, 2009), and about two hundred
thousand to four hundred thousand hectares of land are under sweet potato
cultivation. Yields of sweet potato root tubers have increased from farmers’
pre-research era of about 3 tonnes per hectare to 20-30 tonnes per hectare due
to the availability of enhanced varieties (NRCRI, 2009). Ezeano (2006) showed
that total annual production of the crop in Cross River, Ebonyi and Enugu
States of Nigeria increased from 37,080 to 84,393 tonnes from years 2000 to
2004. Similarly, its consumption as food increased from 3,740 to 7,650 for the
three states within the same period, utilization as feed increased from 440 to
1,020 tonnes, export to neighbouring countries increased from 3,070 to 17,810
tonnes, while domestic sales increased from 27,440 to 50,870 tonnes (Ezeano,
2006).
Sweet potato is
traditionally used as boiled root tubers eaten with stew, boiled and pounded
with either boiled or fermented cassava as fufu or boiled or pounded yam. It is
used as gruel (‘ogi’) porridge after drying and milling as sweetening, chopped
into chips, dried and boiled with beans or vegetables, and fried in vegetable oil, in addition to
processing into flour for sweetening ‘kunu’ or pap.
Sweet potato
is cultivated within 48oN to 40oS of the equator with
altitude from 0-3000m above sea level (Woolfe, 1992; Vaeasey et al., 2008; Low et al., 2009; Troung et al., 2011).
The plant needs ambient day and night temperatures of 15 to 33oC for
optimal growth and root development. Temperature above 25oC is seen
as optimal for maximum growth (Woolfe, 1992). The crop grows best with a well
distributed rainfall of 600 to 1600mm (Low et
al., 2009). Too much rainfall may worsen weed issues and consequently
reduce the yield (Harrison and Jackson, 2011). The crop is widely cultivated
under rainfed situations and is quite drought tolerant. Sweetpotato thrives on
a well-drained soil with a pH of 5.5 to 6.5 (Woolfe, 1992). It needs enough
sunlight; moreover, it can stand at 30 to 50% decrease of complete solar
radiation (Troung et al., 2011).
Sweet potato and
potato are the only root and tuber crops that can be grown and harvested within
four months in Nigeria. Specifically, sweet potato can be cultivated twice or
thrice annually with supplementary irrigation (Nwokocha, 1993). It has low soil
fertility requirement and better opportunity cost relative to the other root
and tuber crops such as cassava, yam and cocoyam (Nwokocha, 1993). Sweet potato
is extremely adaptable to fairly marginal soils and unpredictable rainfall, has
high yield per unit of land and labour and guarantees some yield even under bad
climate conditions (NRCRI, 1987; Nwokocha, 1993; Ogbonna et al., 2005). It is, thus, a low input crop. It is a good source
of vitamin C and provitamin A, and can be substituted for maize in livestock
production (NRCRI, 1984; 1989; 1990; Nwokocha, 1993; Anyaegbunam et al., 2008).
Furthermore, its high
yield potentials and brief life cycle lower than twenty weeks make crops such
as yam (Dioscorea spp)
fairly poor competitors for overall industrial thickener (NRCRI, 1989). Sweet
potato is obviously under-explored as a staple food in Nigeria (Nwosu, 2007),
the slight use of sweet potato in Nigeria is clearly due to non-availability of
adequate sweet potato-based recipes that satisfy the food habits of Nigerians
(Aniedu and Oti, 2007).
In the past decades, many herbal extracts have been widely tested and a
myriad of reports have been published listing the usefulness of plant extracts
to control the animal and plant diseases (Leksombom et al., 1998, Opara and Obani, 2010). A good number of evidence
stated the antimicrobial effects of some medicinal plants for plant disease
control (Opara and Obani, 2010). Most plant extracts were reported as efficient
inhibitors of phytopathogenic bacteria such as Pseudomonas and Erwinia
(Leksombom et al., 1998).
1.1 OBJECTIVES
OF THE STUDY
The objectives of
this study are;
i.
To isolate and identify the causal organisms of leaf spot of sweet
potato
ii.
To conduct pathogenicity test to confirm the organisms.
iii.
To compare the effect plant extracts on growth parameters, disease
severity/incidence and on yield.
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