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ISOLATION AND CHARACTERIZATION OF FUNGI ASSOCIATED WITH “SPOILED” TOMATOES

ABSTRACT

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. Thesame 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, MucorPenicilliumand 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.

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.

Objectives

i.        To isolate of fungi organism from spoilt tomatoes in Gwagwalada.

ii.       To characterize and identify of the fungi in spoilt tomatoes.

iii.      To determine the prevalence and pathogenicity of fungal organisms.

iv.      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.

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