ABSTRACT
Report of damage due to stem roton cowpea in some parts of Kaduna and Katsina States calls for urgent attention in finding possible ways of managing the disease.Knowing the status of the disease will help in employing necessary management strategy as it is a prerequisite to any pest management decision. This research was therefore conducted to determine the incidence, severity and causal organism(s) of cowpea stem rot in North – West Nigeria and evaluate some cowpea varieties for their reactions to the causal organism(s). The incidence and severity of cowpea stem rot in farmers‟ fields were assessed in three Local Government Areas each in four cowpea producing states of North – West Nigeria, Kano, Kaduna, Katsina and Zamfara during 2013 and 2014 rainy seasons. The results showed that cowpea fields in Kaduna State had significantly higher incidence (29.09 %) and severity (21.14 %) than those in Kano, Katsina and Zamfara States for the two seasons. Katsina State had the lowest incidence (9.24 %) and severity (7.31 %) of the disease. The fungi isolated from diseased cowpea stem were identifiedas Rhizoctonia solani,Macrophomina phaseolina, Sclerotium sp., Colletotrichum capsici, Fusarium solani and Curvularialunata. Pathogenicity of the isolated fungi on susceptible cowpea variety SAMPEA 10 was conducted and only Rhizoctonia solani reproduced the typical stem rot symptoms observed on farmers‟ fields.
Four inoculation methods: soil drench, injury pinprick, spray and millet grain soil inoculations were used to test the progress of the disease with Rhizoctonia solani. Symptoms which were reddish brown lesions on stem which later girdle the stem at base were observed when inoculum was introduced through pinprick, soil drench and millet grain but no symptoms were observed on cowpea sprayed with the inoculum.
vii
Six improved cowpea varieties (SAMPEA 7, SAMPEA 8, SAMPEA 9, SAMPEA 10, SAMPEA 11 and SAMPEA 12) two accessions (IAR–00–1074 and IAR–07–1050) and four local varieties (Biu local, Maifarin hanci, Kanannado and Dansokoto) were evaluated in the glasshouse and on the field for their reactions to R. solani infection. The R. solani induced symptoms of varying incidence and severity on all the 12 cowpea varieties with SAMPEA 10, IAR-07-1050 and Biu local recording the highest incidence and severity while Dansokoto recorded the least incidence and severity in both glasshouse and field. Correlation analysis showed that stem rot incidence and severity significantly lead to reduced number of pods and grain yield. It is thus concluded that R. solani induced stem rot is wide spread in North – West Nigeria with varying incidence and severity influenced by agro ecological location. The use of cowpea varieties:Dansokoto, Kanannado and SAMPEA 12 should be encouraged by farmers in areas where the disease cause economic yield loss.
TABLE OF CONTENTS
DECLARATION ……………………………………………………………………………………………………. ii
CERTIFICATION ………………………………………………………………………………………………… iii
DEDICATION ………………………………………………………………………………………………………. iv
ACKNOWLEDGEMENTS ……………………………………………………………………………………. v
ABSTRACT ………………………………………………………………………………………………………….. vi
TABLE OF CONTENTS …………………………………………………………………………………….. viii
LIST OF FIGURES ………………………………………………………………………………………………. xi
LIST OF TABLES ……………………………………………………………………………………………….. xii
LIST OF PLATES ………………………………………………………………………………………………. xiii
LIST OF APPENDICES ……………………………………………………………………………………….xiv
1.0 INTRODUCTION ……………………………………………………………………………………………. 1
1.1 Justification of the Study ……………………………………………………………………………. 2
1.2 Objectives of the Study ………………………………………………………………………………. 3
2. 0 LITERATURE REVIEW ………………………………………………………………………………… 4
2. 1 Botanical Description of Cowpea ……………………………………………………………….. 4
2. 2 Origin and Distribution of Cowpea ……………………………………………………………. 4
2. 3 Importance and Uses of Cowpea ………………………………………………………………… 5
2. 4 Nutritional Value of Cowpea …………………………………………………………………….. 7
ix
2. 5 World Cowpea Production Trend ……………………………………………………………… 7
2.6 Cowpea Insect Pests ………………………………………………………………………………….. 8
2.7 Cowpea Parasitic Flowering Plants …………………………………………………………… 10
2. 8 Cowpea Diseases …………………………………………………………………………………….. 10
2. 8. 1 Seedlings diseases ………………………………………………………………………………… 11
2. 8. 2 Stem and root diseases …………………………………………………………………………… 11
2. 8. 3 Foliar diseases ……………………………………………………………………………………… 13
2. 8. 4 Pod diseases ………………………………………………………………………………………… 14
3.0 MATERIALS AND METHODS …………………………………………………………………….. 16
3. 1 Incidence and Severity of Cowpea Stem Rot in the Surveyed Locations ………. 16
3. 2 Isolation and Identification of the Organisms ……………………………………………. 18
3. 3 Pathogenicity Test ………………………………………………………………………………….. 19
3.4 Evaluation of Different Inoculation Methods on the Development of Cowpea Stem Rot in the Glasshouse …………………………………………………………………….. 20
3.5 Evaluation of Cowpea Varieties for their Reactions to the Causal Organism … 20
3. 6 Statistical Analysis ………………………………………………………………………………….. 22
4.0 RESULTS ……………………………………………………………………………………………………….. 23
4.1 Incidence and Severity of Cowpea Stem Rot in the Surveyed Locations ……….. 23
4.2 Isolation and Identification of Fungi …………………………………………………………. 29
4.3 Pathogenicity Test …………………………………………………………………………………… 38
x
4. 4 Evaluation of Different Inoculation Methods on the Development of Cowpea Stem Rot in the Glasshouse …………………………………………………………………….. 42
4.5 Evaluation of Cowpea Varieties for their Reactions to the Causal Organism … 43
5.0 DISCUSSION …………………………………………………………………………………………………. 56
5.1 Incidence and Severity of Cowpea Stem Rot in the Surveyed Locations ……….. 56
5.2 Isolation and Identification of Fungi …………………………………………………………. 57
5.3 Pathogenicity Test …………………………………………………………………………………… 57
5.4 Effect of Different Inoculation Methods on Disease Incidence and Severity on Cowpea Inoculated with Rhizoctonia solani………………………………………………… 59
5.5 Evaluation of Cowpea Varieties for their Reactions to the Causal Organism … 59
6.0 SUMMARY, CONCLUSION AND RECOMMENDATIONS ……………………….. 62
6.1 Summary………………………………………………………………………………………………… 62
6.2 Conclusions …………………………………………………………………………………………….. 63
6.3 Recommendations …………………………………………………………………………………… 63
REFERENCES …………………………………………………………………………………………………….. 64
APPENDICES ……………………………………………………………………………………………………… 71
xi
CHAPTER ONE
1.0 INTRODUCTION
Cowpea {Vigna unguiculata (L.) Walp} is an annual, herbaceous and leguminous plant, with centre of origin and domestication reported to be in Africa (Carlos, 2004). Nigeria is the world largest producer and consumer of cowpea, producing 2.95 million metric tonnes in 2013 (FAOSTAT, 2013). The highest production of cowpea comes from the northern part of Nigeria with most of the production coming from North – East (896.1 metric tonnes) and North – West (577.94 metric tonnes) geopolitical zones (NAERLS and PRSD, 2012). The annual production is high, but the average grain yield per hectare in Nigeria is only 776.31 Kg/ha which though above the average yield worldwide of 521.91 Kg/ha in 2013, but is far lower than yield of 5333.33 Kg/ha and 5132.35 Kg/ha obtained in USA and Occupied Palestinian Territory respectively (FOASTAT, 2013). Singh et al. (1997) reported diseases, insect pests and parasitic weeds as the most important factors responsible for low cowpea yield in Nigeria. How to reduce the wide gap between actual and potential yields is the issue that needs to be addressed by both researchers and development workers. Reduction of the gap through research and development efforts can also lead to improvements in household nutritional levels, incomes and protection of the environment through reduced pressure on land.
Stem rot constitute a constraint to cowpea production in Nigeria (Suleiman, 2010). The disease was reported in Sri-lanka (Fernando and Linderman, 1994), Tanzania, Benin, South Africa(Adandonon et al., 2003)and Nigeria (Onuorah, 1973; Suleiman, 2010) to be caused by a complex of fungi including species of Pythium, Phytophthora, Sclerotium, Rhizoctonia, Macrophomina and Fusarium. Onuorah (1973) reported yield loss of 11 – 40 % caused by stem rot induced by Pythium aphanidermatum, Sclerotium rolfsii and Fusarium solani at Moore plantation, Ibadan.
2
Stem rot is characterised by reddish brown lesions on the stem at soil level which may extend upward to about the fifth node but rarely to the growing tip. The lesions may girdle the stem at the first node or a little below it. The leaf petioles at the nodes and the basal portion of some side shoots are also invaded by the fungus (Onuorah, 1973).
1.1 Justification of the Study
Cowpea is susceptible to a wide range of insect pests and pathogens, which cause damage to the crop at all stages of growth. Soil and seed – borne fungi are among the pathogens that infect cowpea causing stem and root rot, seedling decay and damping – off complex which result in low yield. Stem rot of cowpea in Nigeria was reported by Onuorah (1973) and Suleiman (2010). Report of incidence of cowpea stem rot by farmers in Sabuwa Local Government Area of Katsina State Nigeria in the 2011 cropping season was made. This was followed by observation of the disease symptoms on research fields of IAR, Samaru (IAR Unpublished report). These reports are indications that the disease is becoming important in North – West Nigeria. However, little or no information is hitherto available on the occurrence and distribution of the disease.
According to Isubikalu et al. (2000), most farmers have some knowledge on methods of controlling insect pests but have little knowledge of controlling cowpea diseases. The most frequently used control measure against pests and diseases is by synthetic pesticides usage whose intensive and indiscriminate use in agriculture has caused many problems to the environment. Such problems include water, soil, animals and food contamination; poisoning of farmers; elimination of non-target organisms; and selection of pest and weed tolerance to certain pesticides (Nidhi and Trivedi, 2002). Alternative control measures of plant diseases include cultural control, biological control, regulatory
3
control and the use of crops resistant to certain pests and diseases. The use of resistant crop varieties is the most economical, easiest, safest and one of the most effective means of managing plant diseases in crops (Agrios, 2005). It is therefore important to give appropriate research attention to finding cowpea varieties resistant to stem rot so as to minimize losses caused by the disease in a manner that will not pose threat to the environment, human and beneficial animals.
1.2 Objectives of the Study
The objectives of this research are to:
i determine the incidence and severity of cowpea stem rot in North – West Nigeria,
ii determine the pathogenicity of fungus associated with the disease and
iii evaluate some cowpea varieties for their reactions to the causal organism.
IF YOU CAN'T FIND YOUR TOPIC, CLICK HERE TO HIRE A WRITER»
