Fungal species associated with the spoilage of some edible fruits in Maiduguri Northern Eastern Nigeria.
Fruits and vegetables are vital sources of nutrient to human beings. They give the body the necessary vitamins, fats, minerals and oil in the right proportion for human growth and development. Fruits and vegetables however, have serious challenges to their existence. These include changes in climatic condition, pest, inadequate rainfall and fungal attack. Over the years, there has been an increase in the need to identify and isolate the fungi associated with their spoilage.
Spoilage refers to any change in the condition of food in which the food becomes less palatable, or even toxic; these changes may be accompanied by alterations in taste, smell, appearance or texture. (Paul et-al 1978) Numerous microbial defects (signs and symptoms) of agricultural crops are characterized by the types of microorganism responsible for the deterioration; the process of infection in the case at fungal invasion follows the development of fungal penetrating structure (appresorium). Colonization of fungi is a critical phase in the microbial spoilage of post harvested fruits. The colonization process involves the ability of the microorganism (fungi) to establish itself within the produce (host). This is initiated when fungi (following adhesion and release of enzymes) depolymerises certain specific cell wall polymers (such a protopectin, the cementing substance) of the produce . Susceptibility of fruits and vegetables is largely due to differential chemical composition such as pH and moisture contents. The higher pH (near neutrality) and moisture contents are associated with their greater predisposition to fungal spoilage. The occurrence of fungal spoilage of fruits is also recognized as a source of potential health hazard to man and animals. This is due to their production of mycotoxins (naturally occurring toxic chemical often of aromatic structure) compounds which are capable of including mycotoxicoses in man following ingestion or inhalation. They differ in their degree and manner of toxicity .
The contamination of fruits and vegetables by fungi could also be as a result of poor handling practices in food supply chain, storage conditions, distribution, marketing practices and transportation .
Fungi affecting Tomatoes (lycopersicum esculentus) includes Fusarium Oxysporium, Fusarium moniliform, Aspergillus niger and Rhizopus Stolonifer. They are responsible for Tomato soft rot, as was isolated by . Result on the percentage incidence and rot shows that Rhizopus Stolonifer caused the greatest rot on tomato fruit. A lot of breading works have been carried on Tomato up to the point where we now have Tomato hybrids that could withstand adverse environmental condition and are resistant to diseases and pests .
The preponderance of the isolated moulds from Orange(Citrus sinensis) belongs to Aspergillus species, and this confirms their prevalence in foods and fruits exposed to tropical humid climate thus constituting potential health risks to consumers of this fruit and it's by products .
Aspergillus niger, Aspergillus flavus, Rhizopus nigrican, Curvularia lunata, Rhizopus oryzae, Fusarium equiseti and Fusarium moniliforme were responsible for post harvested losses in Pawpaw (Caricapaya) in southern Nigeria . Fungi such as Phytopthora cinnamoni, Aspergillus niger and Candida sp also attack Pineapple (Ananas comosus) .
Materials and method
The fruits Caricapaya, lycopersicum esculentus, Citrus sinensis and Ananas comosus both fresh that those with spoilage signs were purchased from three different markets which are Maiduguri Monday Market, custom market and Gidan madara fruit shop in Borno state of Nigeria. A total of forty-four fruits comprising eleven fruits from each fruit type were purchased. Among each of the eleven fruits, there were three infected or spoilt and eight healthy looking fruits. All together there were twelve rotten fruits. The fruits were put in 90% ethanol sterile polyethene bags and transported to the laboratory for analysis.
Isolation of fungi from each of the blemished fruits was carried out using the method of Amusa et.al  and Bariyewu et.al . Segments (3-5cm) of tissues from the margins of the rotted fruits were cut with a sterile scalpel and placed on the previously prepared sabouraud dextrose agar in Petri dishes and incubated at 28+ 1[degrees]c for 5 days. The detected fungi were carefully isolated into pure cultures on Sabouraud Dextrose Agar in plates and slants. The plates and slants were grown for seven days in an incubator preset at 28[degrees]C. Fugal isolates from plates were prepared into mounts on microscopic slides. These were prepared into mounts on microscopic slides. These were examined under the microscope for comparison of fungal morphology with descriptions given by Samson and Reenen-Hoekstra 
Pathogenicity of Isolated Fungi:
Three healthy fruits from each sample were surface sterilized with 90% ethanol, and incisions were made on them using a sterile 4mm cork borer; similar sterile cork-borer was used to cut pellets of agar containing the cultures of fungal mycelia of the isolates. These fungi were then inoculated into the hole created on the healthy fruits in a laminar flour chamber. The inoculate wound was sealed with petroleum jelly. Two controls with incision but not inoculated were established
The inoculated fruits and the controls were placed in a clean polyethene bag (one fruit per bag) each moistened with-wet balls of absorbent cotton wool to create a humid environment and incubated at 28[degrees]c for 5 days. After 72 hours, the inoculated fruits were observed for symptom development. The causal agents were re-isolated from the infected fruits and compared with the original isolates.
Seven fungal species, Aspergillus Sp, Rhizopus Sp, Candida Sp, Fusarium Sp, Phytophora Sp and Mucor Sp. were isolated from a total of twelve fruits. Aspergillus flavus was isolated from Carica papaya and, Ananas comosus, while Aspergillus niger was isolated from Citrus sinensis), Rhizopus Sp was obtained from Carica papaya and Lycopersicon esculentum, Candida sp was isolated from Citrus sinensis and Lycopersicon esculentum while Fusarium Sp, and Mucor Sp were isolated from Lycopersicon esculentum and Phytophthora Sp from Ananas comosus. (Table 1)
The frequency of occurrence shows that Aspergillus sp had the highest frequency occurring in five out of the 12 fruits tested (Table 2). Pathogenicity tests revealed that the isolated organisms were pathogenic. They were able to produce the same spoilage signs in the healthy fruits into which they were re- inoculated. (Table 3)
The fungi found associated with the spoilage of Pawpaw were Aspergillus flavus sp. and Rhizopus stolonifer sp. Baiyewu et al  reported that Aspergillus sp. and Rhizopus Sp, which is the same genus with those isolated from pawpaw in this study, as responsible for the soft rots of Pawpaw in southwestern Nigeria. Aspergillus niger and Candida tropicalis. were found associated with deterioration of orange; this is in line with the work of Niji et al  who reported that Aspergillus Sp. is the predominant organism associated with the spoilage of orange. The isolation of Phytophthora Sp., Aspergillus flavus and Candida tropicalis from pineapple is in line with the work of Efiuvwevwere  who reported that Aspergillus sp. and Candida Sp. is responsible for rotting of pineapple. The isolation of Fusarium oxysporum, Rhizopus stolonifer and Mucor Sp. from tomato confirmed the studies of Chuku et.al , Purse Glove , and Efiuvwerwere  who reported that Fusarium Sp, and Rhizopus stolonifer is responsible for the soft rot of tomato. Onyia et.al.  also reported that Fusarium monilifome, Aspergillus niger and Rhizopus stolonifer were isolated from rotten tomato fruits.
The prevalence of fungi as the spoilage organism of fruits and vegetables is due to a wide range of factors which are encountered at each stage of handling from pre-harvest to consumption and is related to the physiological and physical conditions of the produce as well as the extrinsic parameters to which they are subjected . Damage inflicted on produce at the time of harvest is a major cause of infection since most of the spoilage microorganisms invade the produce through such damage tissues; similarly, the extent of deterioration is influenced by the depth of the wound. Furthermore, the incidence of infection is worsened by poor sanitary practices such as cross-contamination, contact infection during the transportation of produce .
Colonization of fruits and vegetables by the invading microorganism is a critical phase in the microbial spoilage of produce. The colonization process involves the ability of the microorganism to establish itself within the produce. This is initiated when the microorganism (following adhesion and release of enzyme) degrade certain specific cell wall polymers such as protopectin, the cementing substance of the produce. The magnitude of the symptoms of the induced disease is a reflection of the extent of colonization . Whereas both fruits and vegetables are highly susceptible to microbial spoilage, there is a variation in the susceptibility which is due largely to the differential chemical composition such as pH and moisture contents Thus, the lower pH and moisture contents of the fruits makes them more prone to fungal spoilage Efiuvwevwere,  also reported that high moisture and relative humidity led to greater fungal growth in agricultural produce and thus low storability of fruits and vegetables.
Fruits and vegetables are very important and have high dietary and nutritional qualities. Pawpaw fruit can be freshly eaten or cooked. It can also be used in the preparation of jellies, juice and jams. It has great application in the preparation of fruit salad and desserts orange juice is made from fresh healthy oranges. Sweet orange oil is a by-product of the juice industry produced by pressing the peal. Pineapple can be used to prepare juice and fruit salad. Tomatoes are eaten raw or cooked. Large quantities of tomatoes are used to cook soup, juice, sauce, puree, paste and powder, seeds contain 24% oil and this is extracted from the pulp and residues of the canning industry .
The high prevalence of some fungi demand that appropriate control measures against infection, should be employed if farmers expect good performance of their produce. Adequate microbiological knowledge and handling practices of these produce would therefore help minimize wastes due to deterioration and unacceptability. The high moisture content of fruits and vegetables will be a serious limiting factor in their preservation. The fruits used in this study are not produced in the metropolis they are transported to the city from distant places in locally woven baskets and sacks under weather conditions that encourage the incubation of these contaminating microorganisms. It is therefore important that both the farmer who harvests the fruits into bags for transportation, the marketers and consumers take necessary precaution in preventing contamination and also try to create an environment that will not encourage the growth or multiplication of microorganisms. This will help in preventing the consumption of contaminated fruits thereby reducing the risk of poisoning by aflatoxin and other mycotoxins which are produced by these fungi that have been isolated in this study.
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[2.] Baiyewu, R.A., N.A. Amusa, O.A. Ayoola, and O.O. Babalola, 2007. Survey of the post harvest Diseases and Aflatoxin Contamination of Marketed Pawpaw Fruit (carica papaya) in south western Nigeria. African journal of Agricultural Research, 2(4): 178-181.
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Akinmusire, O.O., Department of Microbiology University of Maiduguri, Borno Nigeria E-mail: email@example.com
Department of Microbiology University of Maiduguri, Borno Nigeria
Akinmusire, O.O.: Fungal Species Associated with the Spoilage of Some Edible Fruits in Maiduguri Northern Eastern Nigeria
Table 1: Identification of fungal isolates from fruit samples showing different spoilage patterns. Fruit sample Spoilage Macroscopic examination Carica papaya Sunken large depression Colony white then light yellow-green, becoming dark yellow-green. Carica papaya Water soaked wrinkled Whitish becoming appearance with brown black with depression age Ananas comosus Sunken large depression Colony white then light yellow-green, becoming dark yellow-green. Ananas comosus White deposit, fruit Creamish white become spongy with colonies, opaque, gas production smooth, convex, entire and butyrous Ananas comosus Whitish foamy-like Bluish-brown colour growth with sunken appearance, a long depression branched thread-like filament of cell called hyphae Citrus sinensis Dark brown discoloration Black colonies with sunken spots Fruits white edges become spongy with gas production Citrus sinensis Fruit becoming spongy Creamish white with gas production colonies, opaque, Sunken spots smooth, convex, entire and butyrous Lycopersicon Water soaked wrinkled Whitish becoming esculentum appearance and brown black with depression age Lycopersicon Water soaked wrinkled Colony gray becoming esculentum appearance and Brownish-gray with depression age. Lycopersicon Whitish-pink Colonies are esculentum mycelial growth whitish-pick with a purple tinge mycelium extensive and cottony in culture Fruit sample Microscopic examination Organism Carica papaya Conidial heads are Aspergillius flavus radiate, later splitting into several loose columns. Conidiophores hyaline, coarsely roughened vesicle is globose and flask-shaped phialides that produced chains of rough conidia are borne directly on the vesicle. Carica papaya Non septate mycelia Rhizopus stolonifer Sporangios pores are directly opposite the branched rhizoids. Sporangia are subglobose. sporangiospores are ovoid in shape and columella are subglbose. Ananas comosus Conidial heads are Aspergillius flavus radiate, later splitting into several loose columns. Conidiophores hyaline, coarsely roughened vesicle is globose and flask-shaped phialides that produced chains of rough conidia are borne directly on the vesicle. Ananas comosus Budding, spherical to cells, forming elongate cells, forming pseudomyceliu pseudomyceliu Ananas comosus Zoospore bearing Phytophthora sp flagellate are seen which confirmed homogenous sporangia mortility on the zoospore abundant Citrus sinensis Conidial heads are Aspergillus niger large, globose and dark brown, becoming radiat and splitting into several columns with age. Conidiophore stipes is smooth walled. Conidial heads ar biseriate, and phialides are borne on metula. Conidia are globose and rough walled. Citrus sinensis Budding, spherical to Candida tropicalis elongate cells, forming pseudomycelium Lycopersicon Non septate mycelia Rhizopus stolonifer esculentum Sporangiospores are directly opposite the branched rhizoids. Sporangia are subglobose. sporangiospores are ovoid in shape and columella are subglobose. Lycopersicon Non speptate mycelia Mucor Sp esculentum with branching sporangiophores; columella pyriform, ellipsoidal, pointed conical Lycopersicon Micro-conidia, ovoid to Fusarium esculentum ellipsoidal in shape are oxysporum borne on simple phialides. Macro conidia are borne on phialides on branched conidiospores. Septate fusiform, slightly curved and pointed at both ends Table 2: Frequency of occurrence of each isolate in fruit samples. Fruit Sample Total number Fungal species Percentage of samples frequency Carica papaya 2 Aspergillius 66.7% flavus 1 Rhizopus 33.3% stolonifer Ananas comosus 1 Candida 33.3% tropicalis 1 Aspergillius 33.3% flavus 1 Phytophthora sp 33.3% & Candida tropicalis Citrus sinensis 1 Candida 33.3% tropicalis Aspergillus 66.7% niger Lycopersicon 1 Fusarium 33.3% esculentum oxysporum 1 Mucor Sp & 33.3% Rhizopus stolonifer 1 Fusarium 33.3% oxysporum & Mucor Sp Table 3: Pathogenicity test result Fungal species Fruit inoculated Spoilage pattern produced Aspergillus flavus Carica papaya Sunken spots Ananas comosus Sunken depression Aspergillus niger Citrus sinensis), Dark brown discoloration sunken spots Rhizopus stolonifer Lycopersicon Water soaked esculentum) wrinkled appearance with depression Carica papaya Water soaked wrinkled appearance with depression Mucor Sp Lycopersicon Water soaked esculentum appearance with whitish depression Candida tropicalis Citrus sinensis Fruit is spongy with gas production. Ananas comosus White deposit, fruit become spongy with gas production Fusarium oxysporum Lycopersicon Whitish-pink mycelia Phytophthora sp esculentum growth Ananas comosus 1 Whitish foamy-like growth with sunken depression.
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|Publication:||Advances in Environmental Biology|
|Date:||Jan 1, 2011|
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