Isolation And Characterization Of Fungi Associated With “Spoiled” Tomatoes In Gwagwalada

Project and Seminar Material for Microbiology

Project and Seminar Material for Microbiology


The study examined the various fungal pathogens associated with tomatoes spoilage as well as their preliminary taxonomic grouping up to genus level. 25 samples of the spoiled tomatoes were collected from five locations within Gwagwalada area council. Locations include: Passo Village, Gwagwalada market, Phase III, New Kutunku and Dagiri. The same prevalence rate(100%) was recorded for all tomato samples purchased in all locations.The level of awareness of the general public in regards to the spoilage of tomatoes by Fungi was very significant with about 62.5% of the respondents attesting to the claim of tomato spoilage caused by Fungi and 37.5% disagreeing.

Morphological studies reveal the fungal members which include members of the genus Aspergillus, Cladosporium, Fusarium, Mucor Penicilliumand Rhizopus species. Species of Fusarium were seen to be the most occurring in all samples. Satistical analysis also concurred to the fact that fungi are responsible for spoilage of tomatoes purchached in Gwagwalada (p< 0.05). It implies that fungi are greatly responsible for tomato spoilage. Proper handling, transportation and thorough washing with clean or chlorinated water will go a long way in reducing the risk of tomato spoilage by Fungi.

Table of Contents

Preliminary Page(s)

  • Title page i
  • Certification page ii
  • Dedication iii
  • Acknowledgement iv
  • Abstract v
  • Table of content

Chapter One

1.0 Introduction

  • 1.1 Justification
  • 1.2 Aim And Objectives
  • 1.3 Limitation Of Study
  • 1.4 Hypothesis

Chapter Two

2.0 Literature Review

  • 2.1 Spoilage Of Tomato By Fungi
  • 2.2 Description And Scientific Classification
  • 2.3 Temperature Requirement Of Tomato
  • 2.4 Soil Type And pH Range Of Tomato
  • 2.5 Tomato Diseases
  • 2.5.1 Field Diseases
  • 2.5.2 Transit And Market Diseases Of Tomato
  • 2.6 Factors That Influence Spoilage Of Fruits And Vegetables
  • 2.6.1 Environmental Conditions
  • 2.6.2 pH
  • 2.6.3 Temperature
  • 2.6.4 Nutritional Contents
  • 2.6.5 Oxidation-Reduction Potential
  • 2.6.6 Production Of Antimicrobial Substance
  • 2.6.7 Enzymes
  • 2.7 Toxins Produced By Fungi

Chapter Three

3.0 Research Methodology

  • 3.1 Study Area
  • 3.2 Sample Collection
  • 3.3 Materials, Equipment And Consumables Used
  • 3.4 Sterilization Of Glass Wares
  • 3.5 Preparation Of Media And Processing
  • 3.6 Laboratory Identication And Cultivation
  • 3.7 Preservation And Sub-Culturing Of The Identified Fungi
  • 3.8 Pathogenicity Test Of Isolates On Healthy Tomatoes
  • 3.9 Questionnaire Survey
  • 3.10 Statistical Analysis

Chapter Four

4.0 Results

  • 4.1 Frequency Of Occurrence Of The Pathogenic Fungi
  • 4.2 Pathogenicity Test Of Fungi Isolates On Healthy Tomatoes
  • 4.4 Statistical Analysis Of The Pathogenic Fungi

Chapter Five

5.0 Discussion, Conclusion And Recommendation

  • 5.2 Conclusion
  • 5.4 Recommendation
  • References
  • Appendices
  • Questionnaire

Chapter One

1.0 Introduction

Vegetables constitute commercially and nutritionally important indispensable food commodity. Vegetable naturally play a vital role in human nutrition by supplying the necessary growth factors such as vitamins and essential minerals in human daily diet and that can help to keep a good and normal health. Vegetables are widely distributed in nature. One of the limiting factors that influence the fruit economic value is the relatively short shelf-life period caused by pathogen’s attack (Droby, 2006: Zhu, 2006).

Tomato (Lycopersiconesculentum) pronounced Toh-MAH-to is the most important vegetable worldwide. Tomato is an annual plant which belongs to the Solanaceaefamily which includes other well-known species such as Potato, Tobacco, Pepper and Egg plants (aubergine) and can reach a height of over two meters. It’s a berry fruit, tomato is grown mainly in soil (Frazier and Westhoff,2004).

Tomato is essential mainly for its dietary needs and can be consumed in diverse ways. It can be cooked as vegetable, as an ingredient in many dishes and sauces; in the making of stew, fruit juices and can be eaten raw in salads(Masefield et al., 2002).

The modern day tomatowhich is a very popular fruitoriginated from South-Western Hemisphere, now the Peru-Euador area(Rick,2001).From here,it was distributed to many parts of tropical America. It possibly arrived the West African Ports via Portuguese traders or the Sudan (Tindall, 2004).

Tomato in West Africa is grown in gardens and irrigation schemes. In Nigeria, most tomatoes are grown in the northern parts of the country(Erinle,2007) and there is no record of any systematic or organized traditional storage method for vegetables and fruits. They are usually sold immediately after harvesting. They are packed in baskets, cardboard boxes, or wooden crates ready for transportation to the markets.

Tomato is the most perishable vegetable during handling, transportation and storage. This is because tomato contains large amount of water which makes them susceptible to spoilage by the action of microorganisms such as fungi, bacteria and protozoans (Ross, 1975). Estimates have shown that about one third of the produce is lost before reaching the consumer (Erinle, 2007), this loss has been attributed to a number of factors which include physical (mechanical breakage, bruises), physiological and also damages caused by pathological agents (Thompson and Kelly, 2000), market value of the tomato are mainly reduced by this factors.

Watt and Merrill, (2000) defined spoiled food as that which have been damaged or injured so as to render it undesirable for human consumption. Various activities may result in food spoilage: insect activities,causing physical injuries for example, bruisingand enzyme activity by microorganism causes change in colour, taste, smell, texture and quality of the food.

Pauland Sarisbury, (1981) also referred to spoilage as any change in the condition of food in which the food becomes less palatable or even toxic: these changes may be accompanied by alteration in taste, smell, appearance or texture.

The spoilage of food by microorganisms should not be viewed as a sinister plot on the part of the microbes deliberately to destroy foods but as a normal function of these organisms in the total ecology of all living organisms (Watt and Merrill, 2000). It has also been estimated by Watt and Merrill (2000) that 20% of all fruits and vegetables harvested for human consumption are lost through microbial spoilage causing one or more of 250 market diseases. Spoilage of fresh tomato usually occurs during storage and transit and also while waiting to be processed.

Frazier and Westhoff,(2004) reported that fruits and vegetables after picking continue to respire and as a result heat is produced, this heat is known as ‘vital heat’, the amount which varies with particular amount of fruits and vegetables.

Vegetables that respire more thereby generating most heat are those that perish/spoil most rapidly (Wheeler, 2005). The resulting respiration of the fruits in addition to the normal ripening process complicates an independent discussion on microbiological spoilage of fruits in general and tomato in particular.

Fusarium oxysporium f.sp.lycoperisici andVerticilliumalbo-atrumare two fungi that cause similar wilt disease on tomato.(Nesmith etal.,1983). Fusarium is more common in replant fields and gardens while Verticilliumhas been destructive on greenhouse tomatoes and in commercial stake tomatoes. Verticillium wilt is more of a problem at cooler temperature while Fusarium wilt is considered a warm temperature disease. Both are favoured by wet conditions.

According to Nesmithetal., (1983), both fungi are common inhabitants of Kentucky soils. These fungi attack the plant through the roots and grow up through the water-conducting vessels. FusariumandVerticilliummay be introduced to soils in several ways: Old crop residues, transplants, wind, water,implement-borne soils or mulches. These fungi become established readily in most soils and can remain in the soil for years. When susceptible tomatoes are planted, in infected soil, their roots are also subjected to attack by these fungi. Both diseases are much more serious when accompanied by root knot nematode. These problems can be controlled by using resistant tomato varieties and fumigating or stream sterilizing greenhouse soils.

1.1 Justification

Since microorganisms have been identified with the major cause of spoilage in fruits and vegetables due to their high water content, proper isolation and characterization of these organisms in tomatoes will greatly reduce the spoilage of this perishable fruit and as such producers and consumers will be able to protect their vegetables (tomato) and also identify spoiled tomatoes that have been attacked by fungi.

Works have been done on the isolation and identification of bacteria and fungi on fruits(Okoli, 1998). Little or no work has been done on the isolation and characterization fungi on spoiled tomatoes in Gwagwalada.Therefore, the major organisms responsible for field and market diseases will be majorly identified and checked.

1.2 Aim And Objectives

This research work is aimed at identifying the various fungi organisms associated with the spoilage of fresh tomatoes in Gwagwalada with the view of mapping out strategies to curtail these fungal attacks and also to determine the effects of the isolated fungi on the spoiled tomatoes.


  1. To isolate of fungi organism from spoilt tomatoes in Gwagwalada.
  2. To characterize and identify of the fungi in spoilt tomatoes.
  3. To determine the prevalence and pathogenicity of fungal organisms.
  4. To create public health awareness about the preponderance of fungal organisms.

1.3 Limitation Of Study

Researches have been conducted to ascertain the fact that various microorganisms are responsible for the spoilage of tomatoes. Organisms include Bacteria, for example,Pseudomonas and Xanthomonasspeciesas stated by Watt and Merrill (2000), Fungi, for example, Alternaria, Colletotrichum ,Fusariumand Penicillium species as stated by Barksdale (2001) and other Meioidogyne groups of nematode.

This present study places emphasis on the spoilage of tomatoes in Gwagwalada Area Council caused by pathogenic fungi species.

1.4 Hypothesis

  • H0; Fungi are not responsible in the spoilage of tomatoes.
  • HI; Fungi are responsible in the spoilage of tomatoes.

Chapter Five

5.0 Discussion, Conclusion And Recommendation

5.1 Discussion

The study has determined the various fungal pathogens associated with tomatoes spoilage as well as their preliminary taxonomic grouping up to genus level. The study has also attempted to examine the symptoms developed by these pathogenic fungi species on healthy tomato.From the result of findings, it was seen that a total of 21 isolates were recovered from all the 25 samples of tomatoes as shown in table 2-7, constituting of six fungal genera. The study therefore has indicated that there are a number of fungal pathogens responsible for various diseases. According to the report of Pitt and Hocking (1985) that different genera of fungi which are pathogenic to the fruit lives in the necrotic areas and can cause diseases in humans if consumed directly. Fusarium species (41.4%) were the most frequently occurring fungi genera isolated from all five samples and this is in agreement with the work of Mehrotra (2001), who reported that Fusariumspecies were the most frequent fungal pathogenthat caused fruits’ rots and rusts caused by fungal pathogen.

Pathogenic fungi could be attributed partly to environmental conditions prevailing in the storage systems of vegetables. Singh (2001) had also shown that high temperature favours the growth of these pathogenic fungi while hot and humid weather confers a most conducive atmosphere for the growth of pathogenic fungi on vegetables. According to Singh (2001), cool temperature and dry or low humidity reduces the rate of multiplication of fungal propagules. This might be the reason why vegetables when kept in the refrigerator, last longer despite their being perishable. This is true going by an earlier report of Coursey and Proctor (1975) that metabolic activities generally decreases with decline in temperature and the activity of most pathogenic micro–organisms diminishes with reduced temperature.

Another factor that enhances the easy penetration of fruits by these pathogens may be due to the constant wetting to which the fruits are been subjected to by the vendors, which renders the vegetables more susceptible to attacks. Chlorination of water used in wetting of vegetables would reduce the extent of damage caused by the pathogens (Coplin, 1988). Also, observed, was the mode of handling and packaging of the fruits at the market by the vendors and consumers which is unsanitary can lead to contamination of the fruits.According to Chavan et al. (1995), sporulation of fungal spore occurs at relative humidity above 57. 4% and temperature of 120-300C. The water supplied to the fruit during the rainy season when the trial was conducted was enough to aggravate the rate of sporulation and infection.

As shown in table 6, the results of the pathogenicity test that was carried out showed that all the organisms were pathogenic and were the actual causal agents of spoilage in tomatoes. The test also established the fact that fungi cause deterioration of fruits when they gain entrance into them through mechanical injuries such as bruise and wounds as noted by Zitter (1985).

The isolation of these pathogens is also in line with the work ofGupta and Pathak (1985), Baiyewu (1994), Baiyewu and Amusa (1999), Baiyewu et al. (1994, 2007) and Chukwuka et al. (2010) who also isolatedFusarium and Rhizopus sppfrom tomatoes.

From the 50 questionnaires, 80% (40) of the respondents answered while 20% (10) of the respondents did not answer. It was observed that most people (67.5%) use a close mode of transportation (polyethene bags) to transport there tomatoes when purchased while a few (22.55 and 10%) use an open mode of transportation (baskets and crates) to transport the vegetable when purchased. Heat, microorganisms and mechanical forces are the major factors responsible when a closed mode of transportation is used, while microorganisms, insects and mechanical forces are factors responsible when an open mode of transportation is used. It can therefore be said that, microorganisms and mechanical forces are the major factors responsible for the spoilage of this vegetable as they are common to both modes of transportation. As a result, microorganisms may gain entrancethrough physical damages caused by mechanical forces. About 62.5% of the respondents attested to the fact that fungi are responsible for the spoilage of tomatoes in Gwagwalada and 37.5% disagreed to this fact as shown in appendix 4.
Statistical analysis (ANOVA) had shown that fungi are greatly responsible for the spoilage of tomatoes purchased and sold in Gwagwalada(p<0.05). This implies that there is a significant difference.

5.2 Conclusion

This study affirmed the fact thatfungi are responsible for the spoilage of tomatoes in Gwagwalada. Most of the categories of respondent also supported this claim from the questionnaire conducted. From the research work, Fusarium (41.4%)species was the most occurring pathogen while Rhizopus (4.8%)species was rarely isolated. The prevalence rate of spoilage of tomatoes by fungi in major locations in Gwagwalada is a 100%.From the pathogenicity test that was carried out, it was revealed thatmechanical injuries such as bruises or cuts that occur during harvesting, post-harvesting and packing could provide infectious sites for spoilage pathogens. These infectious sites can therefore be greatly reduced and brought to a minimal by proper storage and handling of the vegetable.

5.4 Recommendation

From the research, to reduce the risk of afflation and other mycotoxins that are deleterious to human health, which are produced by these fungi, it is recommended that;

  1. The thorough washing of harvested tomatoes with clean or chlorinated water, proper cleaning and sanitation of ware houses and disinfection of packaging containers, proper handling of the vegetable during harvest should be done to prevent bruises and scars or other mechanical injuries.
  2. The inhibition of fungal growth by lowering storage temperature through storage under refrigeration of less than 100Cbut not freezing and the use of fungicides when stored by drying.
  3. It is important for both the farmers who harvested the tomatoes into baskets for transportation, the marketers and consumers take necessary precaution in preventing contamination of these tomatoes.

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