ABSTRACT
Laboratory experiments were carried out to investigate the fungitoxic potentials of some plant extracts and Trichoderma harzianum in the management of post-harvest fungal deterioration of potato. The experiments were laid out in Completely Randomized Design (CRD) and replicated three times and data collected were subjected to analysis of variance (ANOVA) using Genstat discovery edition 1.Significant treatment means were seperated using Fisher’s least Significance Difference L.S.D at 5% level of probability. Pathogenicity test revealed that Aspergillus niger, Rhizopus stolonifer Aspergillus flavus, Fusarium oxysporum and Alternaria solani caused rot on potato tubers by utilizing the substrate for their growth development. A. niger was found to be more virolent having the highest rot incidence of 77.5%, followed by R. stolonifer, A .flavus and F. oxysporum with rot incidence of 66.5%, 59.7%, 53.3% respectively, whereas the A. solani depicted a lower pathogenic effect with rot incidence of 33.6%. The result of the inhibitory potentials of the extracts of A. indica, M. oleifera (stem), M. oleifera (leaves) and C. odorata against the five fungal pathogens showed significant differences (P<0.5) in their rates of fungitoxicity on A. niger, A. flavus, R. stolonifer, F. oxysporum and A. solani. The effect of A. indica extract gave the highest means inhibitory effect of 65.4% on A. niger while the least means growth inhibition of 18.4% was recorded by C. odorata extract on R. stolonifer. The results obtained when plant extracts were applied after inoculation with spore suspension fungi isolates showed high significant effect in rot incidence and severity. C. odorata was less effective in controlling the mycelial growth and thus, had the highest percentage diseases incidence of 50.2% .The lowest incidence of rot (21.6%) was recorded with A. indica extract. R. stolonifer showed a stronger resistance to the plant extracts than A. niger, A. flavus, F. oxysporum and A. solani. Results obtained from laboratory screening of T. harzianum for antagonism towards fungal isolates of potato tuber rot, showed that mutual inhibition was observed whenT. harzianum was co-inoculated with -A. solani, A. niger, A. flavus and F. oxysporum, while R. stolonifer overgrew the mycelium of T. harzianum on a PDA. The results of this study have shown the fungitoxic potential of these plants materials and antagonistic effects of T. harzianum in the control of the postharvest rot of potato which could be exploited as alternative to synthetic fungicide in the control of potato rot incited by fungal rot organisms.
TABLE
OF CONTENTS
Title
Page i
Declaration ii
Certification
iii
Dedication iv
Acknowledgements v
Table
of Contents vi
List
of Tables vii
List
of Figures viii
Abstract ix
CHAPTER 1: INTRODUCTION
1.1 Background
of the Study 1
1.2 Economic
Importance of Potato 2
1.3 Diseases
and Other Constraints in Potato Production 4
1.4
Post-Harvest Losses 4
1.5
Aims and Objectives 5
CHAPTER 2: LITERATURE
REVIEW
2.1 History
of Potato Production in Nigeria 6
2.2 Classsifiction
of Potato 7
2.3 Diseases
of Potato 8
2.3.1 Fungal
diseases 8
2.3.2 Early
blight 8
2.3.3 Late
blight 8
2.3.4 Wart
disease 9
2.3.5 Stem
canker and black scurf 9
2.3.6 Pink
rot 10
2.3.7 Watery
wound rot 10
2.3.8 Dry
Rot 11
2.3.9 Charcoal
rot 11
2.4 Bacterial
disease 12
2.4.1 Bacterial
wilt 12
2.4.2 Bacterial
soft-rot 12
2.5 Viral
Diseases of Potato 13
2.6 Control
of Postharvest Tuber Rot Diseases 15
2.6.1 Biological control of rot organisms 15
2.6.2 Chemical
Control 15
of fruits while
the growth and 2.6.3 Use
of resistant varieties 17
2.6.4 The
use of plant extracts 18
2.6.4.1. Moringa (Moringa oleifera Lam) 19
2.6.4.2 Siam
weed (Chromolaena odorata .L) 20
2.6.4.3
Neem (Azadirachta indica. Jus) 21
2.7 Phytochemicals 21
2.7.1 Flavonoids 22
2.7.2 Phenols 22
2.7.3
Saponins 23
2.7.4 Tannins 23
2.7.5 Alkaloids 24
2.7.6 Mechanism
of action of phytochemicals 24
CHAPTER
3: MATERIALS
AND METHODS
3.1 Experimental
Location 26
3.2 Sources
of Materials 26
3.3
Sterilization of Materials 27
3.4
Preparation of Culture Media 27
3.5 Isolation
of Fungal Rot Organisms from Diseased Potatoes 27
3.6 Subculturing and Purification of Fungi
Isolates 28
3.7 Identification and Characterization of Purified
Fungal Isolates 29
3.8 Pathogenicity
Test for Fungal Isolates 29
3.9
Preparation of Plant Extracts 30
3.10
Evaluation of Extract Purity 31
3.11 Effect of Plant Extracts on Fungal Growth 31
3.12 In Vivo
Screening of Plant Extracts against the Fungal Isolates on Potato 32
3.13 Dual
Culture Method 34
3.14 Microscopic
Observation 34
3.15 Experimental
Design 35
3.16 Data
Analysis 35
CHAPTER 4: RESULTS AND DISCUSSIONS
4.1 Results 36
4.1.1 Isolation
of fungal pathogens from diseased potato tubers 36
4.1.2 Pathogenicity Test 38
4.1.4 Effect
of plant extracts on the radial mycelia growth of the isolates 40
4.1.5 Effect
of different plant extracts on the incidence and severity of potato
tuber
rot caused by fungi 42
4.2 Discussion 49
CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS 54
REFERENCES 56
APPENDICES 69
LIST OF TABLES
1: Percentage Frequency occurrence of
isolated fungi from
Diseased potato tubers on PDA at 25-27±20C 36
2: Pathogenicity Test and mean percentage
rot of fungal isolates inoculated on healthy
potato after 7 days, incubated at 25-27±20C 38
3: Percentage inhibition of the radial
mycelia growth of four fungal
isolates by
various plant extracts at different concentrations, 41
4: Effect of plant extracts on rot
incidence of potato tubers inoculated
with A.
niger, A. flavus, R. stolonifer, F. oxysporum and A. solani
and incubated for 7
days at 25-27±20C 43
5: Effect of plant extract on the severity of rot on potato tubers
inoculated with A. niger, A. flavus, R. stolonifer, P. oxysporium
and A solani and incubated for 7
days at 25-27±20C 44
6: Reaction between Trichoderma harzianum and some fungi
isolates
from diseased Potato tubers co-inoculated on PDA at
25-27±20C
for 3days. 45
LIST OF FIGURES
1: Healthy potato tubers 37
2: Diseased potato 37
3: 9cm Petri dishes inoculated with
diseased potato slices, showing
emerging fungal mycelium after 5days
incubation at 25-27±20C 37
4: Pure culture of isolated Aspergillus niger after 5days growth in
a
petri dish incubated at 25-27±20C. 37
5: Potato tubers inoculated isolated fungi
organisms 37
6: Cross section of potato tubers
inoculated with isolated
Aspergillus
niger 37
7-12:
Pathogenicity test with fungal isolates
after 7days inoculation in
healthy potato tubers incubated at 25-27±20C 39
13:
Mycelium of Trichoderma harzianum (A) alone (control) 46
14: Mycelium of T. harzianum (A) invaded by mycelium (G) on PDA,
indicating the outer marging of the
antagonists (arrowed) 46
15:
Mycelium colony of T. harzianum (A- aggressor) overgrowing
colony of Aspergillus flavus (D victim) on PDA with spores of (A)
formed mainly over the colony of (D) 47
16:
Mycelium of T. harzianum (A) overgrowing colony of Aspergillus
niger (C) on PDA with
spores of (A) formed mainly over the
colony of (C) 47
17: Mycelium of T. harzianum (A-aggressor) overgrowing colony
of Fusarium
oxysporium (E-victim) on PDA, with spores of (A)
formed mainly over the colony of (E) 48
18:
Mutual inhibition between mycelial
colonies of T. harzianum (A)
and
Alternaria solani (H) on PDA between the two colonies 48
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND
OF THE STUDY
Potato (Solanum tuberosum L.) belongs to the solanaceae family.It is a
temperate crop, requiring low minimum temperatures of 150C or lower
for tuberization (Okalebo et al.,
2002).It can grow upto 60cm high depending on the variety (Kudi et al., 2008).It is a native of theWestern
Hemisphere and is believed to have originated somewhere between Mexico and
Chile, possibly in the Andes highlands of Bolivia and Peru. It later spread to
other places like England and Ireland. Potato
was introduced into Nigeria in the later part of the 19th century and early
20th century by Europeans notably the tin miners in the Jos Plateau (Demign et al., 2004).It isnow an important and
fast growing tuber crop in Nigeria. Although it is ranked 4th after
cassava, yam, sweet potato, irish potato and cocoyam among the major root and
tuber crops in Nigeria.It is by far the most efficient tuber crop in the
country in terms of tuber yield and days of maturity (Thornton, et al., 2007).Under tropical conditions,
potato matures in about 75 to 90 days as compared to 9 and 12 months for yam
and cassava respectively.Because of the short maturity two or more crops of
potato are possible in a year.It has the highest productivity among the
tropical root crops.
The
world total production is about 324.4 million tons planted on 18.6 million
hectares of land (FAO, 2010). China is the worldlargest producer of potato with
about 74.8 million tons, followed by India and Russia (FAO, 2013).
The
current potato production in Nigeria is 800,000 tones per annum. In terms of
tuber yield, 10-15 times per hectare have been reported in Jos under farmers
conditions (Demign et al., 2004).Most
important potato producing areas of Nigeria are Jos, Plateau, Kano, Zaria,
Mambila, Biu and Obudu highlands. About 95% of the total production comes from
Jos plateau. It is a major source of income among the rural farmers in the designated
areas in Nigeria and many African communities (Wug, 2012).
The
production and marketing of potato in the highland zones of Plateau State has
become an integral part of rural economy, both at the rainy and dry season as
it is cultivated as a rain-fed and dry season crop. According to Okonkwo et al.,(2009), planting of rain-fed
potato takes place from late March to August depending on local conditions while
harvest occurs three to four months later, from July to November. Irrigated
production starts from late October through January with harvest in January,
February, March or April.
1.2 ECONOMIC
IMPORTANCE OF POTATO
To
underscore the importance of potato in addressing the world food crises, the United
Nations declared 2008 as the international year of the potato in order to raise
its profile in developing nations calling the crop “hidden treasure” (FAO, 2008a). Potatoes are of great importance nutritively and
industrially. Nutritionally, potatoes is one of the world's most nutritive sources of food for
both humans and animals, the crop can be processed into portage with palm oil,
chips, flour and use for feeding animals, (Dale, et al.,2003). The ratio of protein to carbohydrates is higher in
potato than in many cereals and other root crops. Industrially, fresh potato
tubers are sliced and sieved to produce starch, various use of starch include
laundry purposes, hardening of textures, this starch is used in the
pharmaceutical industries and in the production of alcohol and wines. Even the
so called potato waste could be liquefied and fermented to produce fuel-grade
ethanol. Potato starch is also a completely biodegradable alternative to
polystyrene and can be use to create plastic items such as plastic dish, forks
and spoons. Potato starch is also being developed as a biodegradable packaging material
(Zealand, 2008)
Potato
contains higher crude fibre than any other root and tuber crops and because of
the low calorie and high vitamin C content it is an important nutritive food (Weaver
and Marr, 2013). The tubers contain carbohydrates 14.2%, protein 4.7%,ash 5%,
fat 07%, Fibre 0.8% vitamin 69%, Calcium 1%, Iron 14%, Magnissium 6%,
Phosphorus 8%, Potassium 9% and Sodium 6% (Odebumni et al., 2007), Potatoes are eaten boiled fried and in stews and it
is also grown for livestock feed and industrial purposes (Dale, et al.,2003)
In
a more recent study, Storey and Anderson (2010) reviewed that individuals who consumed
potato had significantly higher vegetable and potassium intakes than non-consumers.
In adddition, the proportion of potassium and dietary fibre contributed by
potato was higher than the proportion they contributed to total energy.Among potato
consumers aged 14-18 years, potatoes provided 23 percent of dietary fibre and
20 percent of potassium but only 11 percent of total energy in the diet.
Potatoes are also one of the best nutritional values in the produce department,
providing significantly better nutritional value per dollar than many other raw
vegetables (Drewnowski and Rehm, (2013) examined the nutrient density per unit
cost of the 46 most frequently consumed vegetables as part of the National
School Lunch Program (NSLP), and found that potatoes and beans were the least
expensive sources of not only potassium but also fibre. Specifically,
potassium-rich potatoes were almost half the cost of most other vegetables,
making it moreaffordable to meet key dietary guidelines for good health
(Achike, 2004).
1.3 DISEASES
AND OTHER CONSTRAINTS IN POTATO PRODUCTION
Potato
production is characterized by rapid and significant fluctuations in demand and
supply.While average potato yield in North America andWestern Europe often
reach 40 tonnes per hectare,yields in developing countries are usually below 20
tonnes per hectare. The national average potato yields for Kenya has been
reported at 7.7 tons/ha, butthis figure has fluctuated considerably over recent
years, from over 9.5 ton/ha to around 7.5 ton/ha (FAO, 2008). The low yields
have been attributed to poor agronomic practices, low use of inputs especially
fertilizers, low soil fertility, limited access to good quality seeds, diseases
(especially bacterial, fungal, and viruses) and insect pests (Nganga, et al., 2002).The most serious fungal
diseases include late blight (Phytophthora infestans), early blight (Alternaria solani) and watery rot (Pythium ultimum),dry rot (Fusarium oxysporum).Farmers attempt to
plant as early as possible in the season to escape the blight attacks (Chuwang,2010).
Late blight attacks usually occur during mid-July through August (Chuwang,
et al., 2007). Viral diseases,
particularly leaf roll, X and Y viruses can cause severe local damage.Bacterial
wilt (Pseudomonas solanacearum) is a major constraint of potato
production in Jos Plateau State, for which farmers have no effective control.Important
pests include nematodes (Meloidogyne javanicus) and mealy bugs (Planococcus
citri) (Chuwang,et al., 2007).Fertilizers
and pesticides are being used at rates below economic optimum since farmers
direct theirresources to other high value ‘important’ crops such, onions,
tomatoes, barley, tea, coffee, maize, beans and wheat (Nganga, et al., 2002).
1.4 POST-HARVEST
LOSSES
Post-harvest
losses of potato tubers are high and it could be due to poor storage facilities
and attack by fungal pathogens and Post-harvest Physiological Deterioration.,
PPD (Udoudoh, 2011).Enormouspost-harvest losses have been attributed to fungal
deteriorations. Post-harvest fungal pathogens either infect the produce on farm
or develop during storage (Okigbo,2002, 2003,Shukla et al.,2012) .Wounds and bruises which occur mostly during
processes of harvesting and
transportation constitute points of
entry for these microorganisms (Arya, 2010).In
East Africa, Potato tubers
infected with storage fungi have been reported to cause loss of
nutrients, discoloration, mouldy smell and taste and presence of mycotoxins
(Natural Resources International LTD,2004).In Southeast Nigeria, several fungal
pathogens have been associated with
potato tuber rot and include: Botryodiplodia theobromae,
Fusarium solani, Fusarium oxysporum, Aspergillus niger, Rhizopus stolonifer,
Cylindrium clandestrium, Macrophemina phaseolina, Penicillium oxalicum.The
most virulent were P. oxalicum and A.
niger (Okigbo et al.,2009a;2009b).
1.5 AIMS AND OBJECTIVES
Were
to;
· determine
some fungal pathogens causing potato tubers rot of potato
· determine
the incidence and severity of each fungal
agent
· evaluate
the efficacy of three plant extracts;Neem
(Azadirachta indica),Siam weed (Chromolaena
odorata), Moringa leaf and stem (Moringa
oleifera) and Trichoderma harzianum
on tuber rot of potato
.
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