INTERACTION BETWEEN MELOIDOGYNE INCOGNITA AND BOTRYODIPLODIA THEOBROMAE ON MANIHOT ESCULENTA (CASSAVA) AND ITS BIOCONTROL STRATEGIES: IMPLICATIONS FOR SUSTAINABLE CASSAVA PRODUCTION

INTERACTION BETWEEN MELOIDOGYNE INCOGNITA AND BOTRYODIPLODIA THEOBROMAE ON MANIHOT ESCULENTA (CASSAVA) AND ITS BIOCONTROL STRATEGIES: IMPLICATIONS FOR SUSTAINABLE CASSAVA PRODUCTION

ABSTRACT
Cassava (Manihot esculenta) remains a critical staple and industrial crop in tropical agriculture, yet its productivity is severely constrained by complex interactions between plant-parasitic nematodes and fungal pathogens. This study investigates the interaction between the root-knot nematode (Meloidogyne incognita) and the fungal pathogen (Botryodiplodia theobromae), both of which contribute significantly to yield decline and post-harvest deterioration in cassava. The research further evaluates the effectiveness of biological control agents, particularly Glomus mosseae and Paecilomyces lilacinus, as sustainable alternatives to chemical nematicides. A combination of pot and field-based experimental designs was employed under controlled and natural infection conditions to assess pathogenicity, disease synergy, plant growth response, yield parameters, and nematode reproduction. Results from previous empirical findings indicate that both pathogens independently reduce vegetative growth, tuber yield, and quality, while their combined infection significantly intensifies damage severity and tuber rot incidence. Conversely, biocontrol treatments demonstrated substantial reductions in nematode populations and gall formation, while enhancing plant vigor and yield performance. The findings highlight the ecological importance of integrated pest management (IPM) strategies in cassava production systems and emphasize the need for sustainable biological approaches in managing soil-borne pathogen complexes.

CHAPTER ONE: INTRODUCTION

INTERACTION BETWEEN MELOIDOGYNE INCOGNITA AND BOTRYODIPLODIA THEOBROMAE ON MANIHOT ESCULENTA (CASSAVA) AND ITS BIOCONTROL STRATEGIES: IMPLICATIONS FOR SUSTAINABLE CASSAVA PRODUCTION

1.1 Background to the Study
Cassava (Manihot esculenta Crantz) is a perennial root crop widely cultivated across tropical and subtropical regions, serving as a major source of carbohydrates and livelihood security for millions of households. Its resilience to drought, poor soils, and marginal environmental conditions makes it a strategic crop for food security in sub-Saharan Africa. However, cassava production is increasingly threatened by biotic constraints, particularly soil-borne pathogens such as plant-parasitic nematodes and pathogenic fungi.

Among these, the root-knot nematode (Meloidogyne incognita) is recognized as one of the most destructive nematode species affecting cassava, causing root galling, impaired nutrient uptake, stunted growth, and significant yield losses. Simultaneously, fungal pathogens such as Botryodiplodia theobromae are responsible for stem and tuber rot, leading to post-harvest deterioration and reduced market value of cassava produce.

Recent agronomic studies have shown that the interaction between nematodes and fungal pathogens can intensify disease severity through synergistic mechanisms, where nematode infection predisposes plant tissues to fungal invasion. This disease complex has become a major concern in tropical root crop production systems, particularly in environments where farmers rely heavily on vegetative propagation and limited soil management practices.

The increasing resistance of pathogens to chemical control methods and the environmental concerns associated with synthetic pesticides have shifted scientific attention toward biological control strategies. Microorganisms such as arbuscular mycorrhizal fungi (Glomus mosseae) and nematophagous fungi (Paecilomyces lilacinus) have demonstrated potential as eco-friendly alternatives for suppressing soil-borne pathogens and enhancing plant health. Their role in integrated pest management systems offers a sustainable pathway for improving cassava productivity.

1.2 Statement of the Problem
Despite cassava’s economic importance, yields remain far below potential due to persistent infestations by nematodes and fungal pathogens. Most studies have focused on single-pathogen effects, leaving a gap in understanding the interactive dynamics between M. incognita and B. theobromae. Additionally, reliance on chemical control measures has proven unsustainable due to environmental toxicity, high cost, and declining efficacy. There is therefore a critical need to explore pathogen interactions and evaluate environmentally safe biocontrol options suitable for cassava production systems.

1.3 Objectives of the Study
The main objective of this study is to examine the interaction between Meloidogyne incognita and Botryodiplodia theobromae on cassava and evaluate the effectiveness of biological control agents in managing their impact.
The specific objectives include:
i. To determine the pathogenic effects of M. incognita on cassava growth and yield
ii. To assess the interaction between M. incognita and B. theobromae on cassava performance
iii. To evaluate the effectiveness of Glomus mosseae and Paecilomyces lilacinus in controlling M. incognita
iv. To analyze the impact of biocontrol agents on cassava yield and nematode population dynamics

1.4 Research Questions
i. What is the effect of M. incognita on cassava growth and yield?
ii. How do M. incognita and B. theobromae interact in affecting cassava productivity?
iii. How effective are biocontrol agents in suppressing nematode populations?
iv. What is the impact of biological control on cassava yield improvement?

1.5 Significance of the Study
This study provides valuable insights into the complex interaction between nematodes and fungal pathogens in cassava ecosystems. The findings will contribute to improved understanding of disease complexes in root crops and support the development of sustainable integrated pest management strategies. It also offers practical recommendations for farmers, agronomists, and policymakers on reducing reliance on chemical pesticides while improving cassava productivity and food security.

1.6 Scope of the Study
The study focuses on cassava production systems affected by M. incognita and B. theobromae, with emphasis on their interaction and biological control using G. mosseae and P. lilacinus. The research is limited to agronomic performance indicators such as plant height, tuber yield, galling index, and nematode population density.

1.7 Conceptual Overview of Key Pathogens and Biocontrol Agents
Plant-parasitic nematodes, particularly root-knot nematodes, are microscopic soil organisms that invade plant roots and disrupt physiological functions. Meloidogyne incognita is highly adaptive and widely distributed in tropical soils, making it a major constraint to cassava production.

Botryodiplodia theobromae is a fungal pathogen associated with stem and root rot diseases, particularly in post-harvest storage conditions. Its infection results in tissue degradation and reduced shelf life of cassava tubers.

Biological control agents such as Glomus mosseae (arbuscular mycorrhizal fungus) enhance plant nutrient uptake and induce systemic resistance, while Paecilomyces lilacinus parasitizes nematode eggs and reduces population density in the soil ecosystem.

1.8 Justification of the Study
Given the environmental and economic limitations of chemical pesticides, there is increasing global interest in biological alternatives for pest management. Understanding pathogen interactions and biocontrol mechanisms is essential for developing resilient cassava production systems. This study contributes to sustainable agriculture by promoting eco-friendly solutions that align with modern integrated pest management frameworks.

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Siddiqui, Z. A., & Mahmood, I. (1999). Role of fungi in biological control of plant parasitic nematodes. Bioresource Technology.