ISOLATION AND IDENTIFICATION OF FUNGI RESPONSIBLE FOR TOMATO SPOILAGE

ABSTRACT

Tomato is a major vegetable crop that has achieved tremendous popularity over the last century. It is an important vegetable crop across the world. However it is susceptible to spoilage by fungi and bacteria. This study was carried out to isolate and identify fungi associated with spoilage of tomatoes sold in tomato depot Umuahia, Abia State. This reveals the major fungal isolates belong to Aspergillus niger, Aspergillus flavus and Penicillium species. The total fungal count of the tomato fruit under deterioration process for seven days indicates that there was an increase from day one to the seventh day of the deterioration (Table 4.1). The total fungal count increased from 2.1 x 104cfu/g to 3.1 x 104cfu/g from the first day to the seventh day respectively. The percentage occurrence of fungal isolates accessed on the selected tomato fruits revealed that Aspergillus niger was the most frequently occurring fungal isolate with a percentage occurrence of (44.4%), followed by Aspergillus flavus with percentage occurrence of (33.3%) whereas Penicillium species had the least percentage occurrence of (22.2%). With the number of isolated fungi from the selected fruits, it can be concluded that different fungal species occurred within the tomato fruit samples under study. The Hazard Analysis Critical Control Points (HACCP) should be employed at every point in the postharvest chain to minimize contamination.

TABLE OF CONTENTS

Title Page                                                                                                                                 i

Certification                                                                                                                           ii

Dedication                                                                                                                              iii

Acknowledgements                                                                                                                iv

Table of Contents                                                                                                                   v

List of Tables                                                                                                                          vii

Abstract                                                                                                                                  viii

CHAPTER ONE

1.0       Introduction                                                                                                                1         

1.1       Aims and Objectives                                                                                                  4

CHAPTER TWO

2.0       Literature review                                                                                                        5

2.1       Isolation, Identification and Pathogenicity of Fungal Organisms Causing

Postharvest Spoilage of Tomato Fruits During Storage                                             5

2.2       Brief History of Tomato Cultivation                                                                          7

2.3       Tomato Production and Postharvest Spoilage in Nigeria                                          8

2.4       Over-View of Disease Symptoms Due to Fungi in Tomato                                      12

2.4.1    Sour rot                                                                                                                       12

2.4.2    Rhizopus rot                                                                                                               12

2.4.3    Buckeye rot                                                                                                                 12

2.4.4    Black mold                                                                                                                 13

2.5       Physiological Disorders of Tomato                                                                            13

2.6       Control of Postharvest Diseases and Losses of Tomato                                            14

2.6.1    Biological control                                                                                                       14

2.6.2    Chemical control                                                                                                        16

2.6.3    Physical methods                                                                                                        17

2.6.4    Heat treatment                                                                                                            17

2.6.5    Waxing and coating                                                                                                    18

2.6.6    Social and institutional constraints in postharvest disease management               18

CHAPTER THREE

3.0       Materials and Methods                                                                                               20

3.1       Samples Collection                                                                                                     20

3.2       Materials Sterilization                                                                                                20

3.3       Samples Processing                                                                                                    20

3.4       Isolation of Fungi                                                                                                       20

3.5       Identification of the Isolates                                                                                       21

3.5.1    Macroscopic Examination                                                                                          21

3.5.2    Microscopic Examination

CHAPTER FOUR

4.0       Results                                                                                                                        22

4.1       The total fungal counts of the samples                                                                       22

4.2       Cultural Morphology and Microscopic Characteristics of the Fungal            

Isolates from the tomato samples                                                                               22

4.3       The percentage occurrence of the fungal isolate                                                        22

CHAPTER FIVE

5.0       Discussion, Conclusion and Recommendation

5.1       Discussion                                                                                                                   26

5.2       Conclusion                                                                                                                  28

5.3       Recommendation                                                                                                       28

REFERENCES

LIST OF TABLES

CHAPTER ONE

1.0       INTRODUCTION

The Lycopersicon esculentum M. (tomato) is an important vegetable crop across the world, originated in West South America. The fruits of tomato are popular throughout the world and are used in all kind of stews, soups and also eaten raw in salads. Ripe tomato fruits have high nutritive values, being a good source of vitamin A, B, C and minerals ((Wogu and Ofuase, 2014). Because of the importance of tomato as food, it has been bred to improve productivity, fruit quality, and resistance to biotic and a biotic stresses. Tomato has been widely used not only as food, but also as research material. Tomato is a major vegetable crop that has achieved tremendous popularity over the last century. It is grown in every country of the world-in outdoor fields, greenhouses and net houses. Tomato plants can grow up to 10 feet tall, but most species are less than three feet tall on average. Tomato plants are perennial, have a weak stem that often sprawls over the ground and vines over other plants (Sravanthi and Gangadhar, 2015). Fruit of tomato are diverse in size and shape, ranging from small and round to large and variable shapes (Brewer et al., 2006). The size of tomato varies depending on the plant species. Cherry tomato plants produce small, cherry-sized tomatoes. Tomato fruits contain high amount of carbohydrates, fats, organic acids, water, minerals, vitamins and pigments. Tomato fruits are used in garnishing various cooked food in Nigerian dishes as well as dishes in many other parts of the world. It is estimated that ripe tomato fruits contain approximately 94 % of water, 4.3 % carbohydrates, 1 % protein, 0.1 % fat, 0.6 % fibre and vitamins. Antioxidant phytochemicals such as the carotene and lycopene are contained in tomatoes (Wogu and Ofuase, 2014; Sravanthi and Gangadhar, 2015). They are good sources of natural antioxidants which include carotenoids, vitamins, phenolic compounds, flavonoids, dietary glutathione, and endogenous metabolites and have been shown to eliminate free radicals, (Sravanthi and Gangadhar, 2015.

Naturally, Fruits and vegetables carry epiphytic micro flora. During growth, harvest, transportation and further processing and handling the produce can be further contaminated with non pathogenic and pathogenic organisms from soil, human or animal sources. Outbreaks of food borne illnesses have been recorded in Europe, Japan, United States, Canada and Turkey (Gosh, 2009). Pathogenic fungi, such as Altternaria, Aspergillus, Fusarium, Mucor sp., Penicillium, Rhizopus, and Trichoderma have been implicated in some crop spoilage. Fungi contamination of many agricultural products, including tomatoes starts in the fields. Both the biological and physical damages during the harvest and transportation phases, coupled with large amount of water and soft endocarp makes tomatoes more susceptible to spoilage by fungi (Onuoral and Orji, 2015). Few studies on fungi associated with tomato spoilage are available in Nigeria (Eni et al 2010: Wogu and Ofuase, 2014; Bashir et al., 2016).

Tomato is a widely consumed fruit eaten in both raw and processed forms. It has the botanical name Lycopersicum Esculentum and belongs to the plant family solanaceae. It is rich in vitamins including vitamin A and vitamin C, carbohydrates, proteins, fats, fibres and potassium. It is rich in lycopene which has many beneficial health effects. It contains large amount of water which makes it more susceptible to spoilage by the action of microorganisms. Tomato has a much lower sugar content than other fruits and is therefore not as sweet.  Tomatoes may be pear-shaped, elongated, flattened and heart shaped. They are edible, fleshy and reddish when ripe and vary in their acid composition, with white and yellow ones being less acidic. Tomatoes can be used as savoury or flavouring in soups and cooked foods or can be eaten as fruits. It is used in many dishes, salads, sauces and drinks and can also be dried and ground into pancakes (Wogu and Ofuase, 2014).

The consumption of tomatoes throughout the world is believed to benefit the heart and other organs. The richest source of lycopene is tomato and tomato-based products. Lycopene has been found to prevent prostate cancer, improve the skin’s ability to protect itself against the harmful ultra violet rays, decrease the risk of breast, lung, stomach, bladder, uterine, head and neck cancers, protect against neurodegenerative diseases, lower urinary tract infections and reduce the cardiovascular risk associated with type 2 diabetes (Zdenka et al., 2010). Tomatoes have serious challenges to their existence. These include changes in climate conditions, pests, inadequate rainfall and microorganisms particularly fungi. One of the limiting factors that influence tomato economical value is its relatively short shelf life caused by pathogen attack. Spoilage of tomatoes are those adverse changes in the quality of tomatoes that are brought about by the action of predominantly biological and physical factors. These may be changes in taste, smell, appearance or texture of the fruits. Fungi affecting tomatoes include Aspergillus phoenicis, Absidia spp, Trichoderma spp, Alternaria alternata, Fusarium oxysporum, Fusarium moniliformis, Aspergilli us niger, Mucor spp, Rhizopus stolonifer, Penicillium spp, Geotrichum spp and Phytophthora spp (Etebu et al., 2013). Fungal spoilage of tomatoes has been recognized as a source of potential health hazard to humans and animals due to the fact that they produce mycotoxins which are capable of causing mycotoxicoses (diseases caused by fungi toxins) in man following ingestion or inhalation (Zdenka et al., 2010). The mycotoxins are not limited to their areas of infections. Since tomatoes contain large amount of fluid, these mycotoxins diffuse rapidly throughout them, contaminating all parts and making the fruits unfit for consumption. The importance of tomato in the food industry and its nutritional benefits cannot be overemphasized. Routine microbiological examination of tomatoes is very crucial as it contributes to a large extent to economic development.

1.1       AIMS AND OBJECTIVES

The aim of this study is to isolate, and identify fungi species associated with spoilt tomatoes in tomato depot Urbani Ibeku market, Umuahia, Abia state, Nigeria.

The objectives are.

•       Isolation and identification of fungi contaminants responsible for spoilage of tomato fruits.

•       To determine the average fungal counts of the spoilt tomato fruits

•       To determine the percentage occurrence of the fungal isolates in the spoilt tomato fruits  

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