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ABSTRACT

The fungitoxic properties of ethanolic and aqueous leaf extracts of Azadirachta indica and Ocimum  gratissimum  used  for  the  control  of  post-harvest  fungal  diseases  of  Solanum melongena were tested in vitro with benlate serving as the standard fungicide and water as the bank control.  Three  fungal  species,  Aspergillus  niger,  Rhizoctonia  solani  and Mucor ramosissimus were isolated from diseased S. melongena fruits kept at room temperature on laboratory tops for10 days. The fruits started showing signs of decay after 4 days of exposure. Growth on the fruits at the  sites of the rot suggested  the  presence  of fungal pathogens. Isolation and culturing of these pathogens gave the  identified species as the causal agents. Pathogenicity  test  confirmed  them  as  the  causal  organisms  of  the  fruit  rot.  The  three pathogens  were treated  with both  ethanol  and aqueous  leaf extracts  of the two  plants at concentrations  ranging  from  25  to 100%  and  benlate  at concentrations  between  2.5  and

10.0%.  Various concentrations of the extracts were added to prepared Potato Dextrose Agar (PDA)  media.  The pathogens  were  inoculated  separately  into  the  PDA  media  and  were incubated for eight days. Fungitoxic effects of these extracts on the mycelial growth of the pathogens  were  significant  at  P  ≤  0.05  for  all  treatments.  The  three  pathogens  were completely inhibited by the two plant extracts for both the aqueous and ethanolic extracts at

100% concentration.  With respect to ethanolic extract, O. gratissimum was more  efficient than A indica, but the reverse was the case with aqueous extracts. Ethanolic  extracts were generally more effective than the aqueous extracts. Ethanolic leaf extract of O. gratissimum may be used to effectively control post-harvest fungal diseases of S. melongena.

CHAPTER ONE

1.0    INTRODUCTION

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.

1.1      AIM AND SPECIFIC OBJECTIVES OF THE RESEARCH

The specific objectives of the research are to :

1.         Isolate and identify the pathogens responsible for the post-harvest fungal diseases of garden egg.

2.        Determine the frequency of occurrence for each of the fungal isolates.

3.        Estimate the disease severity in the infected garden egg.

4.        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.


This material content is developed to serve as a GUIDE for students to conduct academic research



FUNGITOXIC EFFECT OF ETHANOLIC AND AQUEOUS LEAF EXTRACTS OF AZADIRACHTA INDICA A. JUSS, OCIMUM GRATISSIMUM LINN AND BENLATE IN THE CONTROL OF POST-HARVEST FUNGAL DISEASES OF SOLANUM MELONGENA LINN (EGG PLANT)

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