moringa oleifera disease of orange-fleshed …...biodeterioration of sweetpotato, environmental...

Nigerian Journal of Mycology Vol. 11 (2019) 26

BIOACTIVITY AND PHYTOCHEMICAL COMPOSITION OFMORINGA OLEIFERA IN THE MANAGEMENT OF FUNGAL ROT

DISEASE OF ORANGE-FLESHED SWEETPOTATO

*Dania, V.O. and Thomas, A.S.

Dr. Victor Ohileobo DANIA, Department of Crop Protection and EnvironmentalBiology, University of Ibadan, PMB 001, UI Post Office, Ibadan, Nigeria.

Telephone: 08053264736; Email: [email protected]

Mr Akintunde Samuel THOMAS, Department of Crop Protection andEnvironmental Biology, University of Ibadan, PMB 001, UI Post Office, Ibadan,

Nigeria. Telephone: 08022452887, Email: [email protected]

*Corresponding Author: [email protected]

ABSTRACTFungal biodeterioration accounts for significant yield losses of sweetpotato (Ipomoeabatatas L.) in Nigeria. The problems of environmental pollution and pathogen resurgenceassociated with chemical control necessitate an organic approach in the management oftuber rot disease of sweetpotato. Therefore, this study evaluated the efficacy of M. oleiferaLam extracts for the preservation of sweetpotato against rot-inducing fungal pathogens invitro and in vivo. Rot-causing fungi were isolated from infected tubers samples collectedfrom four major sweetpotato producing states: Benue, Edo, Kogi and Kwara in Nigeria.Incidence of fungal isolates, pathogenicity and rot severity were determined usingdestructive sampling method. Phytochemical analysis was carried out to determine thebioactivity of secondary metabolites in the extract. Six fungal genera, Macrophomina,Lasiodiplodia, Rhizopus, Fusarium, Rhizoctonia and Sclerotium were pathogenic tohealthy sweetpotato tubers on reinoculation. Moringa oleifera was effective in the in vitrobioassay and its efficacy was dependent on the extracting solvent, plant part used andpathogen. However, thanolic extract of M. oleifera was most effective with inhibitoryeffect on the mycelial growth of the test pathogens varying between 29.3 and 94.3%. Rotseverity was reduced in inoculated tubers that were treated with M. oleifera extracts by41.4-52.0% at 75% w/v extract concentration in the in vivo trial. Quantitativephytochemical analysis of the extract indicated presence of significant amounts ofphenolics, alkaloids and tannins. Moringa oleifera showed promise in minimizingpostharvest rot of sweet potato induced by fungal rot pathogens

Keywords: Biodeterioration, Destructive sampling, Fungal pathogens, Moringa oleifera,Phytochemical analysis, Rot severity.

NigerJ.mycol Vol.11, 26-45


INTRODUCTIONSweetpotato [Ipomoea batatas (L.)

Lam], which is rich in beta-carotene,provides a source of energy, dietaryfiber, potassium, phosphorus, vitaminsB1, B6 and niacin that help inimprovement of the nutritional content(Burri, 2011). Regardless of theeconomic importance of the crop, it hasa limited shelf-life which makes storageof tubers through the off-season to thenext planting season difficult.Consumers are unable to store the tubersover long periods in anticipation ofhigher prices (Nedunchezhiyan and Ray,2010). The tuber is highly vulnerable todamage during harvesting,transportation to storage, and otherpostharvest operations, especiallybecause of its relatively thin periderm.Injured or damaged tubers provide entryto rot inciting pathogens whether in thefield or during storage. Post-harvestmicrobial rot constitutes a major barrierto production, sales and marketing ofsweetpotato in tropical Africa with lossin income to farmers (Ray and Ravi,2005). Although fungal deterioration oftubers is mainly facilitated bymechanical injuries and favourableenvironmental factors during crucialgrowth stages, the physiological state ofthe tuber could influence post-harvestinfection rate. The organismsLasiodiplodia theobromae, Rhizopusspp., Fusarium spp., Ceratocystis

fimbriata, Rhizoctonia solani,Macrophomina phaseolina, Sclerotiumrolfsii, Curvularia lunata andPlenodomus destruens have beenimplicated in field and postharvest decayof sweetpotato tubers (Ray and Ravi,2005; Nelson, 2008; Ray and Tomlins,2010; Ray et al., 2010).

The infecting fungal pathogenscause localized discoloration and lesionsin tubers leading to degradation oftexture, flavor and appearance.Inadequate transportation and storagefacilities result in losses of harvestedtubers in transit and storage. It isnecessary to develop more viable andcheaper disease control options.Although synthetic fungicides could beused in the management of post-harvestbiodeterioration of sweetpotato,environmental issues, toxicity and highcost make it untenable. Conversely useof botanicals is safe, eco-friendly andcost effective against plant pathogens.

Moringa oleifera is a fast-growingevergreen tree (Anwar et al., 2007) usedas a vegetable (Rebecca et al., 2006)which is adapted to various soil types ofsoil, especially in the tropics, and isdrought tolerant (Fahey, 2007). Theplant possesses antibacterial properties(Anwar et al., 2007; Chaung et al., 2007;Giri et al., 2010). The leaves, roots, seedand bark have been reported to havemedicinal properties (Nikkon et al.,2003; Liu, 2004; Rao and Rao, 2004;

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Ajibade et al., 2005; Anamika et al.,2010). Variation in the distribution andconcentration of phytochemicals in M.oleifera leaves may be influenced byclimatic factors, stage of maturity of theplant (Bamishaiye et al., 2011), and bychoice of solvent, since solvents differin their ability to extract phytochemicalsand solubility (Ray andNedunchezhiyan, 2012).

There is little information on use ofMoringa oleifera in post-harvestmanagement of sweetpotato tuber rotdisease. This research was undertakento evaluate the potential of M. olefieraextract in preservation of stored sweetpotato against post-harvest fungalbiodeterioration.

MATERIALS AND METHODSSources of sweetpotato tubers

Infected orange-fleshed sweetpotatotubers of the same variety showingadvanced soft and dry rot symptomswere collected from the sweetpotatoproducing states of Benue (7.35°N,8.83°E), Edo (6.54°N, 5.89°E, Kogi(7.56°N, 6.57°E and Kwara (8.98°N,4.56°E) in Nigeria. Samples werecarefully packed in transparentpolythene bags and labelled fortransportation to the laboratory forisolation of associated fungi. Healthysweetpotato tubers were also collectedfrom the 4 locations. Leaves, seed androots of Moringa , used in in vitro and

in vivo trials, were obtained from theForestry Research Institute of Nigeria,Ibadan, Nigeria.

Isolation and identification of rot-inducing fungi

Decaying sweetpotato tubers were cutinto 2 × 2 mm blocks with a sterilizedscapel. The sections were sterilized in10% sodium hypochlorite for 1 min andrinsed with several changes of steriledistilled water. They were blot-driedwith sterile tissue paper and plated onpotato dextrose agar (PDA) amendedwith 1 mL of lactic acid. Incubation wasat 28±2°C in a Gallenkamp incubator for3-4 days with daily examination of Petridishes for fungal growth prior topurification of isolates. To facilitateidentification, emerging colonies onPDA were purified and identified usingselective media for the respectiveisolates following standard procedures(Gutierrez et al., 2010). Rhizoctoniasolani was purified on a selectivemedium consisting of water agar (Difco)18 g·L-1, Streptomycin sulfate (100mg·L-1), Penicillin-G sodium salt (100mg·L-1) and Sodium hydroxide (800µ·L-1). Culture plates were incubated inthe dark for 24 hrs at 28°C and evaluatedfor number of R. solani sclerotia andcolonies present. The alkaline nature ofthe medium allowed a faster growth ofR. solani colonies compared to thestandard water agar medium.

Control of tuber rot disease of sweetpotato


Macrophomina phaseolina was isolatedusing a selective medium described byCloud (1991) with the followingcomposition: 39 g of potato dextroseagar, 100 mg of rifampicin, 224 mg ofmetalaxyl, 1 mL of tergitol NP-10 and1 L of deionized water. The pathogenwas identified by production ofcharacteristic oval-shaped non-septateconidia. Isolation and identification ofFusarium oxysporum was enhanced bygrowth on selective Komada medium(Komada, 1976), which consisted of thefollowing composition: Na2B4O7.10H2O 1 g·L-1, K2HPO4 1 g·L-1, KCl 0.5g·L-1, MgSO4.7 H2O 0.5 g·L-1, Fe-Na-EDTA 0.01 g·L-1, D-galactose 20 g·L-1,L-asparagine 2 g·L-1, Agar 15 g·L-1 andPCNB (Terraclor 75% WP)(pentacloronitrobenzene) 1 g·L-1. Themedium was amended with oxgall 0.5g·L-1 and streptomycin sulfate 0.3 g·L-1.Sclerotium rolfsii was purified usingselective broth (Backman andRodriguez-Kabana, 1976). One-L of themedium consisted of 1.0 g KH2PO4, 0.5g MgSO4.7H20, 2.0 g KNO3, 1.0 mgthiamine hydrochloride, and 10 mL ofstock solution containing 1 .0 g ofFE2S04.7H20, 1.0 g ZnSO4.7H20 and 0.6g MnSO4.H2O and 30 g of glucose.Morphological growth of Lasiodiplodiatheobromae and Rhizopus stolonifer wasdistinct with production of pycnidiabearing septate conidia andsporangiophores with sporangiospores

respectively on PDA. Selective mediawere not necessary for isolation of thosepathogens. Identification of all fungalisolates was done following descriptionsin Barnett and Hunter (2000) andSamson et al. (2010)

Determination of incidence andpathogenicity

This involved the determination ofdistribution of the fungal isolates acrossthe four states that were surveyed fortuber rot disease. The number ofoccurrence of each fungus in every tuberin all locations was expressed as apercentage of the total number ofoccurrence of fungi from tubers in allthe locations. This was calculatedfollowing the methods of Chuang et al.(2007).Fungal incidence = a/b x100 a = Occurrence of each fungus per tuberin all locations b = Occurrence of fungi per sweetpotatotuber in all the locations

Pathogenicity was evaluated usingthe same fungal pathogens isolated fromrotted sweetpotato tubers. Fresh healthytubers were washed with distilled waterand surface-sterilized using 10% sodiumhypochlorite to eliminate secondarypathogens and contaminants. Mycelialmass and conidia from a 1-week old pureculture were removed with a spreaderand placed into a double layer of cheesecloth following addition of 10 mL sterile

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distilled water and 2 drops of Tween 80detergent. A ten-fold serial dilution wasprepared from the stock solutionfollowing standard procedure byselecting 106 conidia mL-1 from thedilution series as the final inoculumconcentration (Ben-David andDavidson, 2014). A sterilized 3-mmcork borer was used to bore holes 0.5 cmdeep in tubers in the proximal and distalregions which were inoculated with theinoculum concentration. Five tuberswere inoculated for each of the 12 fungalisolates and the experiment wasarranged as a completely randomizeddesign with 3 replications. Steriledistilled water was used in controls.Inoculated and control tubers wereenclosed in sterile, moistened, polythenebags and incubated at 28±2°C for 2weeks. The tubers were cut open at theend of incubation and observed for rotdevelopment. All isolates wereevaluated following Koch’s postulatesfor pathogenicity confirmation.

Preparation of Moringa oleiferaextract

Healthy Moringa leaves, seed androots were collected, washed with tapwater and air-dried at room temperature(28±2°C) for 10-20 days depending onthe tissue type. Dried leaves and seedwere pulverized using a high speedblender (Waring commercial,Springfield, MO) to a fine powder. Cut

root sections were ground using ahammer mill. For each powder sample,25, 50 and 75 g were dissolved in 100mL of cold, sterile distilled water,allowing 2 hr for settling, and the extractfiltered through double-layered cheesecloth. A hot water extract was preparedby infusing ground powder in water bathat 90°C for 2 hr. Ethanol extract wasprepared by dissolving each weight ofground sample in 100 mL of 70%ethanol and allowing 2 hr for settlingbefore filtering through cheese clothpreparatory to further use.

In vitro inhibitory effect of extractson fungal pathogens

An aliquot of 1 ml of each extract wasdispensed into sterile Petri dishes beforeadding 15 ml of potato dextrose agar.The solution was swirled gently to allowproper mixing and then allowed to forma gel in the Laminar flow hood.Thereafter, a 3 mm-cork borer was usedto remove a disc from the culture of eachisolate and placed at the centre of thePetri dish. Control plates consisted ofPDA only without addition of anyextract material. The experimentaldesign was a 3x3x3x6 factorial in acompletely randomized design withthree replicates. The treatmentsconsisted of three plant parts: leaves,seeds and roots; three extracts: Coldwater extract (CWE), hot water extract(HWE) and ethanol extracts (EE) at



three levels: 25%, 50 and 75 w/v sixpathogens: R. solani, L. theobromae, R.stolonifer, F. oxysporum, M.phaseolinaand S. rolfsii. The inhibitory effect ofextract was evaluated thus:Mycelial inhibition = PC-QT x100

PCWhere PC = Average diameter ofmycelia in controlQT = Average diameter of mycelia infungal treatment

In vivo inhibitory effect of extractson fungal pathogens

The experiment was a completelyrandomized design with three replicates.A 75% w/v extract concentration whichhad earlier proved effected in the in vitroassay was used in the in vivo trials.Clean, healthy sweet potato tubers werewashed in running tap water, surface-sterilized with 10% sodium hypochloriteto remove soil-borne mycoflora andrinsed with sterile distilled water. Tuberswere bored to a depth of 0.5 cm at themiddle region using a 3mm-cork borer.The bored section was treated with 1 mlof the extract before inoculation with100µl of 106 spore concentration of eachof the six pathogens. The experimentaldesign was a 3x3x3x6 factorial in acompletely randomized design withthree replicates. The treatmentsconsisted of three plant parts: leaves,seeds and roots; three extracts: Coldwater extract (CWE), hot water extract

(HWE) and ethanol extracts (EE) atthree levels: 25%, 50 and 75 w/v sixpathogens: R. solani, L. theobromae, R.stolonifer, F. oxysporum, M.phaseolinaand S. rolfsii. Bored sections of controltubers were filled with sterile distilledwater. Inoculated tubers were incubatedinside well aerated sterile crates for threemonths. Percent rot reduction wasaccording to Ray and Ravi (2005).

Rot reduction = DC-DT X 100 DCWhere DC = Average diameter of rotin control tubersDT = Average diameter of rot of treatedtubers

Phytochemical analyses of M. oleiferaextract

Cold, hot and ethanolic extracts ofMoringa leaves, seed and roots wereanalyzed for presence of tannins,flavonoids, phenolics, saponins, cardiacglycosides, steroids and anthraquinones.A 50% w/v concentration of the leaves,seed or roots were dissolved in cold, hotwater and ethanol for 3 days. Thereafterthe mix was filtered through cheesecloth and the ethanol content evaporatedusing a sohxlet extractor at roomtemperature. The presence andquantification of tannin content wasevaluated using Folin Ciocalteu assayfollowing standard procedure (Sulaimanand Abd Manan, 2015). An aliquot of

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100 µL was added to 750 µL of distilledwater, 500 µL of Folin Ciocalteu reagentand 1000 µL of 35% Sodium carbonate.The mixture was further diluted to 10mL and stirred vigorously. Thereafter,it was incubated at 28±2°C for 1 h andread at 725 using a UVspectrophotometer (model 10S,Genesys, NY, USA). Total tannins wereexpressed as gallic acid equivalentGAE·g-1 dry matter. Flavonoids wereevaluated using calorimetric analysisand following standard procedure(Proestos et al., 2006). An aliquot of 200µL extract and 150 µL of sodium nitritewas incubated at 28±2°C for 1 hr.Thereafter, 150 µL of aluminiumchloride hexahydrate was added andincubation was for 10 min. An aliquotof 750 µL was added and the mixincubated at 28±2°C for 20 min.Absorbance was read using the UVspectrophotometer at 510 nm. Totalflavonoid was expressed as Quercetinequivalent dry matter. Total phenoliccontent was determined using acolorimetric method (Shahidi andNaczk, 1995). An aliquot of 200 µL ofthe extract was dispensed to a beakercontaining 800 µL of deionized waterand 100 µL of Folin Ciocalteu reagent.The mixture was shaken vigorously andincubated at 28±2°C for 20 min.Thereafter, an aliquot of 300 µL sodiumcarbonate was added to the mix whichwas incubated for 2 h at 28±2°C in the

dark. Absorbance was read at 765 nmusing the UV spectrophotometer. Totalphenolic content was expressed in mggallic acid equivalent dry matter.Evaluation and quantification of thesecondary metabolites saponin, cardiacglycosides, alkaloids, steroids andanthraquinones were carried outfollowing standard procedures (Odebiyiand Sofowora, 1978; Harbone, 1976;Trease and Evans, 1989).

Statistical analysisExperiments were laid out in completelyrandomized design with threereplications. All numerical data wereanalyzed using generalized linear model(GLM) of SAS by analysis of variance(ANOVA). If interactions weresignificant means were separated withTukey’s HSD post-hoc test using SAS(2002).

RESULTS Twelve fungal species were isolatedacross the 4 locations (Table 1).Macrophomina phaseolina had thehighest incidence in Benue followed byLasiodiplodia theobromae. Pythium sp.was the least prevalent fungus associatedwith rotted potato tubers in the state.Lasiodiplodia theobromae was the mostfrequently encountered fungus in Edostate, while species of Pythium andVerticillium were least prevalent.Lasiodiplodia theobromae and M.



phaseolina were the most predominantfungi in Kogi state, Rhizopus stoloniferwas the most prevalent fungus in Oyostate, while S. rolfsii was the leastfrequent. The genera Macrophomina,Lasiodiplodia, Rhizopus, Fusarium,Rhizoctonia and Sclerotium proved tobe pathogenic to healthy sweetpotatotubers on reinoculation. Pythium sp. wasnot pathogenic when artificiallyinoculated to tubers from Kogi andKwara states. Corynespora sp. and A.solani were not pathogenic in two of thestates. Penicillium sp. was notpathogenic on reinoculation to healthysweetpotato tubers in all states.

The root extract of proved to be moreeffective in inhibition of radial mycelialgrowth of R. solani and L. theobromaeat the 25% w/v concentration (Table 2).The extract was effective against F.oxysporum and M. phaseolina at thesame concentration. Ethanolic extract ofMoringa leaves, seed and root wereeffective against R. solani with reductionof radial mycelial growth at 75% w/vconcentration. There was no differencein the effect of ethanolic leaf and rootextracts on the same pathogen.Comparatively, all the Moringa plantparts and extracting solvents were leasteffective against R. stolonifer mycelialgrowth of the test pathogen. All extractsinhibited radial growth of F. oxysporumat the 75% w/v extract concentration.Seed and root extracts were most

effective against M. phaseolina growthinhibition. Ethanolic extract waseffective against S. rolfsii at 75% w/vgrowth inhibition of the test pathogen.There was no difference in inhibitoryeffect of ethanolic leaf, seed and rootextract on S. rolfsii at 75% w/v. All theother treatments differed at lower extractconcentration.

Rot development was reduced intubers treated with leaf, seed and rootextract of M. oleifera (Table 3).Ethanolic root extract was most effectiveduring the first month of storage againstrot caused by R. solani. There was nodifference in effect of hot water andethanolic extract on the pathogen at theend of the 3 months of storage. The rootextract was more effective in rotreduction initiated by F. oxysporum, M.phaseolina and S. rolfsii, while ethanolicextract reduced rot development ininoculated tubers. Cold water extract ofMoringa leaf, seed and root were mosteffective in reducing S. rolfsii rot at 3months of storage. Analysis of varianceshowed significant difference in theinteraction for tissue, solvent andmetabolite (Table 4). Phytochemicalanalysis indicated presence of tannins,saponins, cardiac glycosides, flavonoids,alkaloids, steroids, phenolics andanthaquinones (Table 6). Cold water andethanol extraction affected tannins levelin Moringa leaf, seed or root samples,with ethanolic extract having the highest

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Tab

le 1

. Per

cent

mea

n in

cide

nce

and

path

ogen

icity

of f

unga

l iso

late

s ass

ocia

ted

with

ora

nge-

flesh

edsw

eetp

otat

o tu

bers



Dat

a ob

tain

ed a

t 7 d

ays a

fter

inoc

ulat

ion

of t

est p

atho

gens

; C

WE

= C

old

wat

er e

xtra

ct, H

WE

= H

ot w

ater

ext

ract

, EE

= Et

hano

l ext

ract

Mea

ns w

ith sa

me

lette

rs a

long

a c

olum

n ar

e no

t sig

nific

antly

diff

eren

t usi

ng T

ukey

’s H

SD p

ost-h

oc te

st

Tab

le 2

. In

vitr

o in

hibi

tory

eff

ect o

f M. o

leife

ra e

xtra

ct o

n m

ycel

ial g

row

th o

f viru

lent

rot-i

nduc

ing

fung

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Tab

le 3

. In

vivo

Inhi

bito

ry e

ffec

t of M

. ole

ifera

ext

ract

on

swee

tpot

ato

tube

rs in

ocul

ated

with

viru

lent

rot f

ungi

and

stor

edfo

r thr

ee m

onth

s at 2

8±20 C

Dat

a ob

tain

ed a

t thr

ee m

onth

s afte

r ino

cula

tion

of te

st p

atho

gens

CW

E =

Col

d w

ater

ext

ract

, HW

E =

Hot

wat

er e

xtra

ct, E

E =

Etha

nol e

xtra

ctM

eans

with

sam

e le

tters

alo

ng a

col

umn

are

not s

igni

fican

tly d

iffer

ent u

sing

Tuk

ey’s

HSD

pos

t-hoc

tes



Tab

le 4

. Qua

ntita

tive

phyt

oche

mic

al a

naly

sis o

f M. o

leife

ra e

xtra

ct

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concentration. Tannins were not foundin hot water extract of leaves, seed androots. All solvent extracts containedsaponins with the hot water of rootextract having the highest concentration.Cardiac glycosides were present in coldand hot water extracts of the 3 plantparts. The metabolite was completelylacking in the ethanol extract. Allextracts contained flavonoids andsteroids except hot water leaf extract ofthe active compound. Althoughalkaloids and phenolics were present inall extracting solvents of the plant parts,the ethanolic root extract had the highestconcentration. Anthraquinones werepresent in cold and ethanol extract ofMoringa leaf, seed and roots. However,the metabolite was not found in the hotwater extraction process.

DISCUSSIONPostharvest tuber rot is responsible for

significant losses in stored sweetpotatotubers which reduces quantity andquality of the produce available for saleand consumption. Rot of tubers occurswhen pathogens gain entry through thethin periderm which is easily damagedby cuts, injuries and abrasions. Improperhandling of tubers during harvest canlead to post-harvest losses. Most of thediseases are established in the field andcaused by fungi which are generally themost common rot-causing pathogens insweetpotato. In a related development,

Ray and Tomlin (2010) reported isolatesof Rhizoctonia, Sclerotium andFusarium to influence sweetpotato rotin storage. Tubers infected by thesepathogens were characterized by rapidcollapse and degradation of tissues withrepulsive odor, This could be attributedto action of extracellular enzymesamylases, cellulases and estarasesproduced by pathogens that cause cellwall degradation of infected tubers(Salami and Popoola, 2007; Oladoye etal., 2013). Several plant pathogenicfungi produce metabolites that mayinfluence their growth and ability toinitiate disease and virulence. Themetabolites may include enzymes thathave the ability to hydrolyze thecuticular layer of epidemal plant cells,cell wall degrading enzymes, toxins,hormones and siderophores capable ofdegrading host chemical defense(Lattanzio et al., 2006; Sivaramanan,2013). The ability of tubers to withstandinfection may be because producedphytoalexins that interfered with thecapability of the pathogen to degradehost polymers. Development of diseasewithin harvested produce is dependentto a large extent on the ability of thepathogen to secrete pectolytic enzymeswhich are capable of decomposing thenon-soluble pectic compounds thatcause tissue degradation. This processleads to enhanced permeability of theplasma membranes of attacked cells and



to cell death and facilitates diffusion ofnutrients which can serve as a mediumof pathogen development (Barkai-Logan, 2001).

Moringa oleifera extract inhibitedradial mycelial growth of the pathogensin vitro, as well as rot initiation anddevelopment in sweetpotato tubersinoculated, and treated, with the extractthroughout the storage period relative tothe control. John et al. (2014) reportedthe efficacy of M. oleifera extract in invitro control of Gibberella xylariaoides.The antifungal activity of M. oleiferaextract against the soil-borne fungi R.solani, Pythium and Fusarium has beenreported (Moyo et al. 2012; Dwivedi andEnespa, 2012). The extract of M.oleifera has bactericidal activity againstseveral pathogens (Abalaka et al., 2012;Sankar, 2012; Aldine and Devi, 2014).Moringa oleifera microbial activity isenhanced by presence of zeatin,quercetin, bi-sisterol, caffeoyl quimicacid and kaempferol (Anjorin et al.,2010). The leaf extract was mosteffective against R. stolonifer and S.rolfsii at 25% w/v concentration in vitro.This supports reports that leaves haveexcellent insect repellence andfungicidal attributes (Riad et al., 2014;Zafferi et al., 2015). Inhibitory effectsof the extract on the pathogens increasedwith increased extract concentrationwith best inhibition achieved at 50% and75% w/v concentrations against R.

solani, L. theobromae, F. oxysporumand S. rolfsii. This agrees with Talreia(2010), Seint and Masara (2011) andRiad et al. (2014). Moringa root extractproved to be most effective against thepathogens in in vitro and in vivo trials,followed by the seed extract, while theleaf extract was least effective. Thisagrees with Anjorin et al. (2010) andRiad et al. (2014) that maximuminhibition of several phytopathogenicbacteria and fungi was with M. oleiferaroot extract.

Toxicity of plant extracts to fungimay be due to partial or completeinhibition of mycelial growth, andalternation in physiology andbiochemical activities of fungal cells.Moringa extract was least effective ininhibition of mycelial growth of R.stolonifer in vitro. This could beattributed to R. stolonifer may becapable of degrading phenolicscontained in the extract. It has beenreported that in spite of phenolic toxicproperties, a number of microorganismscan utilize phenol under aerobicconditions as sources of carbon andenergy because their enzymaticmachinery is well suited for degradationof phenolics (Ch.supriya and Deva,2014)

Phytochemical analysis showed thatalkaloids, flavonoids, saponins, tannins,cardiac glycosides, phenols andanthraquinones were present in the

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extracts. Antimicrobial activity of M.oleifera may be due to the presence ofthese phytochemicals. Bukar et al.(2010) identified the presence of theshort polypeptide 4(α-L rhamnosyloxy)benzyl-isothiocyanate in M. oleifera.They argued that the peptide may actdirectly on microorganisms and result ingrowth inhibition by disrupting cellmembrane synthesis of essentialenzymes. Flavonoids are strongantioxidants effective against bacterialmetabolites in vitro and other pathogensby inhibition of membrane boundenzymes due to their antioxidantproperty while tannins are a group ofpolymeric phenolic compounds that areable to kill microorganisms (Sankar,2012). Anthaquinones, terpenoids andsteroids are naturally occurring phenoliccompounds present in Moringa extractshow antibacterial properties byintercalating with bacterial DNA (Satoet al., 2004). The efficacy of M. oleiferaextract against plant pathogens is afunction of the phytochemical it canproduce. The best inhibitory effect onthe pathogens was with the ethanolextract in the in vitro and in vivo trials,indicating the secondary metaboliteswere most soluble and available in theorganic solvent. The amount, type ofmetabolite present, and the antifungalactivity of an extract is largelyinfluenced by the extracting solvent,method of extraction, age of the plant

species, time of harvesting plantmaterials and prevailing environmentalconditions (Sikander et al., 2013).

Phenolic compounds have beenimplicated in disease resistance in manycrops. Some occur constitutively and areconsidered to function as preformed orpassive inhibitors, while others areformed in response to ingress ofpathogens and their appearance isconsidered as part of an active response(Mazid et al., 2011). Phenoliccompounds contribute to resistancethrough antimicrobial properties, whichcan have direct effects on the pathogen.They may enhance resistance bycontributing to healing of wounds bylignification of cell wall. Toxicity oftannins, hydrolysable tannins andproanthocyanidins, usually estimated bymeasurement of reduction of in vitrogrowth of mycelium, is documented forseveral fungi (Lattanzio et al., 2006).

Control of sweetpotato tuber rotdisease depends on understandingdisease-causing organisms, theconditions that promote theiroccurrence, and factors that affect theirability to cause disease. Proper handlingand avoidance of environmental stresswill ultimately help to reduce post-harvest diseases. The efficacy of M.oleifera extract indicates it may be ofuse in post-harvest preservation ofsweetpotato tubers against fungaldegradation.



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S.B. and Adeyemo, S.O. (2012). Theantibacterial evaluation of Moringaoleifera leaf extracts on selectedbacterial pathogens. Journal ofMicrobiolology Research 2(2):1-4.

Adline, J. and Anchana, T.A. (2014). Astudy on photochemical screeningand antibacterial activity of Moringaoleifera impact: InternationalJournal of Research and AppliedNatural Social Science 2(5):169-176.

Ajibade, L.T., Fatoba, P.O., Raheem,U.A. and Odunuga, B.A. (2005).Ethnomedicine and primaryhealthcare in Ilorin, Nigeria. IndianJournal of Traditional Knowledge4(2):150-158.

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