Garden egg (Solanum melongena Linn) of the family Solanaceae (Obeng-Ofori et al., 2007) is a kind of fruit that is very important for man; as food, supplying some major nutrients, and as a source of bioactive ingredients militating against some diseases like diabetes mellitus and liver problems. It is also used for many other purposes among which are to achieve weight control within a short period, eliminate unnecessary salts in maintaining proper functioning of the heart, reduce the sugar content level in diabetics because of its low calorie and high fibre contents and reduce blood cholesterol (Aliyu, 2006). However, the damage caused by pests and microbes often constitute a great impediment to biomass productivity of this plant. It is for example susceptible to fungal diseases caused by Phytophthora nicotianea, var. parasitica and if the fruit touches the ground, Corticium rolfsii will cause an infection (Obeng-Ofori et al., 2007). This has stimulated the search for suitable control strategies against the disease.
Garden egg (Solanum melongena Linn) is commonly referred to as “igba” or”ikan” among the Yoruba, “yalo” among the Hausa and “aňara” in Igbo language. It is a fruit native to India. Today, it is cultivated in many parts of the warmer regions of the world, Africa inclusive. The fruit is often shaped like an egg hence the name garden egg and comes in different colours like green, white, grey or a combination of these colours (Osei et al., 2010). It tastes from bland to sweet or slightly bitter. The over ripped ones are used to make stew, and the stew made with garden egg is palatable. The fruits and leaves are used as vegetables, while the fruits serve as ‘kola’ in ceremonies.
Nutritionally, the fruit when mature for consumption contains 92.7% water, 4% carbohydrates, 1.4% proteins, 1.3% fibre, 0.3% fats, 0.3% minerals and is rich in vitamins A and B. It was reported by Shukla and Naik (1993) that on the average, the oblong-fruit cultivars are rich in total soluble sugars, whereas the long-fruit cultivars contain higher amounts of free reducing-sugars, anthocyanin, phenols, glycoalkaloids, dry matter and amide protein. Salamat et al. (2013) stated that as fruit maturity progresses and sugar content increases, total soluble solid will also increase. The presence of glycoalkaloids is responsible for the bitter taste in egg plant fruit. Low calorie and protein contents make this fruit a perfect recipe for achieving weight loss within a short period, and eliminating unnecessary salt to help maintain proper functioning of the heart. The meaty nature of garden egg makes it a substitute for meat and fish especially for people who have liver problems and for people who should protect their heart against cholesterol (Shukla and Naik, 1993). Some pathogens that infect egg plant fruits at various stages of development and particularly after harvest include the genera such as Phytopthora, Helminthosporium, Hemilleia, Mycosphaerella, and others (Mehrota and Aggarwal, 2003).
Many fruits and vegetables are perishable especially in tropical and subtropical regions without adequate refrigeration. The magnitude of post-harvest losses in fresh fruits and vegetables is estimated at 25.8% (Thirupathi et al., 2006). Most of the product is lost after the harvest because of inadequate handling and preservation methods. People in developing countries often cannot afford the use of cold storage facilities, which may be because of lack of capital or lack of technical knowledge by small scale growers and retailers in these areas (Thirupathi et al., 2006). Fungi are the most important and prevalent pathogens infecting a wide range of host plants, causing damage to the fresh fruits and vegetables during storage and transportation and subsequently economic loss. Various strategies that have been used to control the pathogens include the use of chemical and biological agents. Some notable synthetic chemicals have been developed and used to control these diseases. However, they have been reported to be toxic to both plants and mammals (Chaturvedi et al., 2003), and they are expensive to peasants and subsistent farmers.
Considerable post- harvest losses of fruits are brought about by decay caused by fungal plant pathogens attack (Dianez et al., 2002 and Rial-Otero et al., 2005). The control of these pathogens is of great significance, hence the use of synthetic fungicides which has increased consumer concern because of their carcinogenic effects, residual toxicity problems and environmental pollution (Kumar et al., 2008). Recently, some higher plant products have drawn the attention of some researchers to search for some phytochemicals for exploitation as anti-microbial agents. Shweta (2014) reported that Tricuderma harziamum, T. viride and Pseudomonas fluorescence were found to be antagonistic against Pythium. Such plant products or plant extracts are reported to be specific, biodegradable, cheap, readily available and environmentally safe (Kumar et al., 2008).
Extracts of plants such as A. indica are believed to be efficacious in the control of plant fungal diseases and have been recommended by many international organizations (Chaturvedi et al., 2003; Davendra et al., 2011 and Hasabnis and Souza,1998). Some extracts from neem plant have been shown to be toxic to fungal pathogens, like Poria monticolad infecting wood (Dhyani et al., 2004; Dubey and Dwivedi, 1991). Asperillus flavus from soybean seed (Krishnamurthy et al., 2008) and Pyricularia oryzea infecting rice plant in the field and harvested rice (Amadioha, 2000). Ocimum gratissimum L. have been shown to have several medicinal uses (Ojeifo and Denton, 1993). Leaves of Ocimum gratissimum have been found to exhibit high anti-fungal activities against Fusarium moniliforme, Aspergillus flavus, and Aspergillus fumigatus (Nguefack et al., 2004) and based on convincing in vitro evidence, it is said to be a potential food preservative (Tagne et al., 2000). There are many kinds of products that have been studied in plant protection; some of them are considered to have the ability of inducing plant defense reactions (El Ghaouth et al., 1997; Meir et al., 1998; Wang et al., 2009 and Marin et al., 2003).
Fruits vary in their innate resistance to decay and are most resistant when relatively dry and firm. When fruits are harvested they have limited post-harvest life. They no longer receive water or nutrition from the plant. Naturally occurring senescence in produce leads to softening of the tissues and often loss of preformed antimicrobial substances. These changes in the fruits make them less desirable to consumers (Bartz et al., 2009). The improper handling, packaging, storage and transportation may result in decay of fruits and vegetables (Wilson et al., 1991). Fruits due to their low pH, higher moisture content and nutrient composition are very susceptible to attack by pathogenic microorganisms, which cause rot and produce mycotoxins (Moss, 2002).
Schwartz and Gent (2007) reported that several pathogens are responsible for post-harvest rot of fruits and vegetables; which include pathogenic fungi such as Sclerotinia sclerotiorum, Penicillium spp., Rhizoctonia solani, Phytophthora spp., Pythium spp., Rhizopus spp. and several bacteria such as Erwinia carotovora and E. chrysanthemi. Naureen et al. (2009) also listed a number of fungi such as Alternaria alternate, Aspergillus spp., Fusarium spp., Phytophthora capsici and Rhizopus stolonifer as causative agents of post-harvest diseases of fresh fruits and vegetables.
Whitaker (1990) reported that plant pathogenicity and spoilage of fruits and vegetables by rotting are manifestations of pectinolytic enzymes activity. These pectinases are commercially sourced from fungi (Singh et al., 1993; Singh et al., 1999 ). The enzymes act on pectic substances which are high in molecular weight and negatively charged, and acidic complex glycosidic polysaccharides that are present as calcium and magnesium pectates (Rastogi, 1998). Sakai et al.(1993) reported that the pectic substances account for 0.5 – 4.0% of the fresh weights of plant material, including fruits. These pectinolytic enzymes are widely distributed among fungi, bacteria and many types of yeast; specifically Aureobasidium pullulans and Rhizoctonia solani have been named among others.
Some chemicals are generally toxic to mammals including man. This problem associated with the use of synthetic chemicals necessitated the use of antimicrobial agents of plant origin for the control of post-harvest fungal diseases of plants which is one of the reasons for this research.
- AIM AND SPECIFIC OBJECTIVES OF THE RESEARCH
The specific objectives of the research are to :
- Isolate and identify the pathogens responsible for the post-harvest fungal diseases of garden egg.
- Determine the frequency of occurrence for each of the fungal isolates.
- Estimate the disease severity in the infected garden egg.
- Determine the extent of fungal inhibition by ethanol and aqueous extracts from Azadirachta indica and Ocimum gratissimum leaves and benlate solution.
1.2 STATEMENT OF THE PROBLEM
The need to control pests and microbes that are inimical to high yields on our farms using pesticides cannot be over emphasized. The synthetic pesticides in markets are rather costly for the average farmer, alongside their non biodegradable nature and their not being environmentally friendly and not being readily available in the rural communities, hence the necessity to explore other alternative options that will serve same purpose at an affordable price.