EVALUATION OF CASSAVA CULTIVARS AND INTERCROPPING WITH LEGUMES AS AN INTEGRATED NEMATODE PEST CONTROL STRATEGY IN CASSAVA (MANIHOT ESCULENTA CRANTZ) PRODUCTION

ABSTRACT
These studies on evaluation of cassava cultivars and intercropping with legumes as an integrated nematode control strategy in cassava      production were carried out as greenhouse/microplot and field experiments. Of the 200 cultivars screened for resistance to Meloidogyne spp., only 76 survived and from this lot only 3 lines 77/227, TMS30572 and 73/222, showed any resistance while 7 others namely NR8082, 75.668, 73/238 (Egbenegbe), 73/295, 73/118, 75740(Panya), 82/00661 and 73295B were tolerant. All the other cultivars tested were susceptible. The second experiment, to determine the economic threshold level of the root-knot nematode M. javanica populations on two cassava varieties, showed that, with the exception of the control plants, the root-knot nematode damage was obtained at all levels of the inoculum used and the root-knot nematode populations had no significant effect on the aerial growth parameters like leaf and stake weights. The two cassava varieties differed significantly in the final nematode population in their roots. The economic threshold level was identified as an initial density of 500eggs/plant. The lower pest values obtained for TMS30572 with increase in inoculum density further confirmed it to be resistant to M. javanica.
Intercropping four cassava varieties with four legume types in microplots revealed that nematode at both levels used, (0 and 1,000 eggs/plant) had no significant effect on growth and yield of the cassava but amongst sole and legume-intercropped cassava cultivars, significant differences were obtained. The feeder roots and stake/stem weights of the sole cassava varieties were significantly higher (p>0.05) than their intercropped mixtures with legumes. The highest tuber yield values were observed for NR8083 planted sole (630g/plant) followed by TMS30572 intercropped with bambaranut (537g/plant). Nematode-treated plants were significantly affected when they were destructively sampled for damage symptoms on the cassava. Though no significant effect was observed on yield, the significant nematode damage effects on the cassava indicate that the root-knot nematodes affect the outward appearance, the shelf life and storability of the cassava products. The productivity of the legumes under cassava was significantly different (p<0.05) especially on the aerial plant growth. Generally, the legume leaf, stake and feeder root weights (with a few exceptions) had higher sole values than their intercropped components. The same pattern was evidenced for the number of root nodules, where the sole legume number of nodules was higher than that of the intercrops. Significant legume yield differences (p<0.05) were obtained between NR8082-groundnut (60.62g/plant) and NR8082-bambarranut (17.2g/plant). The observed trend was that the intercropped legumes were lower in seed yield than their corresponding sole components. The number of root nodules had a direct linear relation with legume seed yield. However nematode treatment had no significant effect on the legume growth values. Legumes in intercrop mixtures had lower damage symptoms than their corresponding sole crops and sole groundnut was higher in infection scores right through than its intercropped legume cassava mixture. Notably, significant interaction was obtained in number of nematodes in the roots between the legumes in the mixtures and nematode treatment. The legumes in the mixtures significantly (p<0.05) reduced the damage effect of nematode treatment. The results from the two field sites followed the same trend as those obtained in the microplots. However, for bambaranut its intercrop variety for NR8083, TMS50395 and TMS30572 yielded more than the sole component. NR8083 cassava intercropped groundnut had the highest Land Equivalent Ratio (LER) of 1.811 in Site 1, followed by TMS50395 intercropped groundnut had highest LER (1.626) in Site 2.
In line with the goal of Integrated Pest Management (IPM), integrating use of resistant cassava cultivars and intercropping with legumes has been identified as a successful IPM package for our farmers.

TABLE OF CONTENTS
Title Page
Table of Contents
List of Tables
Abstract

INTRODUCTION

LITERATURE REVIEW
2.1       Economic Importance of the Crop
2.2       Origin, History and Production of the Crop
2.3       Cassava Taxonomy
2.4       Cassava Morphology and Physiology
2.4.1    Root System
2.4.2    Shoot System
2.4.3    Branching
2.4.4    Leaves
2.4.5    Flowering
2.4.6    Growth and Development
2.4.7    Leaf Area Index (LAI)
2.4.8    Leaf Area Duration (LAD)
2.4.9    Dry Matter Production and Partitioning
2.4.10  Environmental Effects on Growth and Development
2.4.11  Cyanide Content
2.4.12  Physical Deterioration of Storage Roots
2.5       Cassava Cultivation: Agronomy and Cropping Systems
2.6       Cassava Mineral Nutrition and Fertilization
2.7       Crop Utilization Storage and Small Scale Processing
2.7.1    Cassava Utilization in Food, Feed and Industry
2.8       Production Constraints of Cassava
2.8.1    Soil Fertility
2.8.2    Pests and Diseases as Constraints to Cassava Production
2.8.3    Economic Importance of Nematodes Generally
2.8.4    Economic Importance of Root-Knot Nematodes in Cassava
2.9       Strategies for Overcoming Constraints
2.9.1    Screening for Resistance
2.9.2    Susceptible and Resistant Host Plants
2.9.3    Resistance Ratings
2.9.4    Mechanism of Resistance in Meloidogyne
2.9.5    Relevance to IPM
2.9.6    Role of Host Plant Resistance in an Ecologically Sustainable Cassava
            Crop Protection Strategy
2.9.7    Prospects of Host Resistance with Biotechnology and other Breeding Programmes
2.9.8    Intercropping Systems
2.9.9    Legume Intercrops
2.9.10.1 Effect of Nematodes on Rhizobial Population
2.9.10.2 Effect of Nematodes on Rhizobial Infection
2.9.10.3 Effect of Nematodes on Nodule Development
2.9.10.4 Effect of Nematodes on Nitrogen Fixation
2.10     Crop Damage
2.10.1  Nematode Crop Damage on Cassava
2.10.2  Nematode Life Cycle
2.10.3  Pathogenicity and Symptoms
2.10.4  Damage and Economic Threshold Level
2.10.5  Nematode Damage Models
2.11     Integrated Pest Management (IPM)
2.11.1  History and Case Studies in the Evolution of IPM as a Control Strategy
2.11.2  Need for IPM
2.12     Pest-Resistant Varieties, Thresholds and IPM
2.13     Problems and Prospects of IPM

MATERIALS AND METHODS
3.1       Cassava Varieties Used
3.2       Legume Types Used
3.3       Land Preparation
3.4       Soil Sampling
3.5       Time of Planting and Crop Spacing
3.6       Raising Root-Knot Nematode Inocula
3.7       Setting-up Cassava Test Plants
3.8       Expt.1: Screening of Cassava Cultivars for Resistance to Root-Knot
            Nematodes Meloidogyne javanica
3.8.1    Setting-up 200 Cassava Test Plants
3.8.2    Preparation of Inocula and Inoculation of Plants
3.8.3    Inoculation of Test Plants
3.8.4    Harvesting of Experimental Products
3.8.5    The Parameters Measured Included
3.9       Expt 2: Effects of Different Root-Knot Nematode (Meloidogyne javanica)
            Populations on Cassava (Manihot esculenta Crantz) Growth
3.10     Expt 3: The Effect of Legumes on Root-Knot Nematodes
            Infestations of Cassava Grown in Microplots
3.10.1  Preparation of Inoculants and Inoculation of Plants
3.10.2  Plant Harvesting and Data Collection
3.11     Expt 4A: The Effect of Legumes as a Control Strategy for Meloidogyne spp
            Infection of Cassava under Natural Populations of the Nematodes in the
            Field (Site 1) in 1999/2000
3.11.1  Plant Harvesting Data Collection
3.12     Expt 4B: The Effect of Legumes as a Control Strategy for Meloidogyne spp
            Infection of Cassava under Natural Populations of the Nematodes in the
            Field (Site 2) in 1999/2000
3.12.1  Growth Maintenance
3.12.2  Parameters Measured at Harvest

RESULTS
4.1       Expt 1: Screening of Cassava Cultivars for Resistance to Root-Knot
            Nematodes Meloidogyne javanica
4.2       Expt 2: Effects of Different Root-Knot Nematode (Meloidogyne javanica)
            Populations on Cassava (Manihot esculenta Crantz) Growth
4.3       Expt 3: The Effect of Legume Types in the Control of Root-Knot
            Nematodes Infecting Cassava Grown in Microplots in 1999
4.3.1    Cassava Productivity
4.3.2    Damage of Cassava in Microplots
4.3.3    Legume Productivity
4.3.4    Nematode Damage of Legumes in Microplots
4.4       Expt 4A: The Use of Legumes as a Control Strategy for Meloidogyne spp
            of Cassava under Natural Populations of the Nematodes (Site 1)
4.4.1    Climatic Conditions and Results of Soil Analysis
4.4.2    Experiment 4A (Site 1)
4.4.3    Cassava Productivity
4.4.4    Cassava Damage:- in Site 1
4.4.5    Legume Productivity:- in Site 1
4.4.6    Damage on Legumes
4.5       Expt 4B: The Use of Legumes as a Control Strategy for Meloidogyne
            spp of Cassava under Natural Populations of the Nematodes in the
            Field (Site 2) In 1999/2000
4.5.1    Cassava Productivity:- Site 2
4.5.2    Cassava Damage:- Site 2
4.5.3    Legume Productivity: - Site 2
4.5.4    Damage on Legumes: - Site 2
4.5.5.1 Total Cassava Yield from the 2 Sites
4.5.5.2 Soil Nematode Population for Site 1
4.5.5.3 Soil Nematode Population for Site 2
4.5.5.4 Land Equivalent Ratio (LER) for the two Sites 1 and 2
4.5.5.5 Comparison of the Productivity of the two Sites 1 and 2
4.5.5.6 Productivity of Cassava Intercropped with Legumes

DISCUSSION
CONCLUSION
REFERENCES
APPENDICES
PLATES

INTRODUCTION
Recognition of the importance of cassava as a vital food staple across Africa from results of collaborative studies, conducted over several years have also brought with it concerns over the declining yields of cassava due to pests and diseases; and have necessitated increasing efforts to eliminate the constraints (Okogbenin, et al., 2007; Njoku, et al., 2009; Egesi, et al., 2009; 2010). However, such efforts have hitherto been embarked upon without proper and accurate assessments of pest and diseases, crop potentials, symptoms of pest damage and feasible and sustainable pest control strategies. And this is where, according to Onyenobi (2000), integrated pest management (IPM) has come into play as the most effective and safest strategy in pest and disease control in maximizing crop protection.

Cassava, Manihot esculenta Crantz is a major tropical root crop found throughout the tropics (Asia, Africa, Oceania and Latin America ) and is vital to the subsistence economies and food security of many less developed nations (Hillocks and Wydra, 2002). It is one of the most important crops in tropical Africa and provides over 50% of the energy requirement for over 300 million people in the continent (Njoku et al., 2009). It has extremely high efficiency for caloric production over a wide range of ecological conditions, particularly on poor soils and with few inputs. It can be stored up to 3 years in the ground, serving as starvation insurance for the small farmer when other crops fail (Luc et al., 1990; Dahinya, 1994; Hillocks, 2002).

More cassava is now being produced in Africa than in South America where the crop originated. In many parts of Africa, several tons of cassava leaves and tender shoots are harvested and consumed as vegetables providing protein (26-41% crude protein on dry weight basis), vitamins and minerals (Hahn, 1984). Cassava has in recent years transformed from famine reserve commodity and rural staple to a cash crop in Africa.

Africa contributes to more than half of global supply, with Nigeria recording more than a third of African production. Nigeria is now the world’s largest cassava producer and its cassava transformation is the most advanced in Africa (Egesi et al., 2006; 2010). The scope for increasing the use of cassava in industries and export market is determined by the development of improved varieties with high traits of protein, beta-carotene; delayed post-harvest physiological deterioration (PPD) with resistance to pests...

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