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Crop Protection 27 (2008) 385–390

www.elsevier.com/locate/cropro

Trichoderma-fortified compost extracts for the controlof choanephora wet rot in okra production

Yasmeen Siddiquia,�, Sariah Meona, Mohd R. Ismailb, Asgar Alic

aDepartment of Plant Protection, Faculty of Agriculture, Universiti Putra Malaysia, Serdang, 43400 Selangor, D.E., MalaysiabDepartment of Crop Science, Faculty of Agriculture, Universiti Putra Malaysia, Serdang, 43400 Selangor, D.E., Malaysia

cSchool of Biosciences, Faculty of Health and Biological Sciences, The University of Nottingham Malaysia Campus,

Semenyih, 43500 Selangor, D.E., Malaysia

Received 24 February 2007; received in revised form 28 May 2007; accepted 6 July 2007

Abstract

The potential of water extracts produced from rice straw (RST) and empty fruit bunch of oil palm (EFB) composts fortified with

Trichoderma harzianum for the control of Choanephora wet rot of okra caused by Choanephora cucurbitarum was studied under field

conditions. Disease severity was lowest in plants treated with Trichoderma-fortified RST extracts (9.56%) with a disease index of 1,

mancozeb (Dithane M-45s (2 g l�1 of water), Trichoderma-fortified EFB compost extracts, extracts of RST and EFB, and an aqueous

suspension of T. harzianum recorded disease severity values of 10.25%, 19.38%, 37.56%, 53.71% and 56.36%, with a disease index of 1,

1, 2, 3 and 3, respectively. There was a reduction of 85.04% in Choanephora wet rot severity on okra treated with Trichoderma-fortified

RST extracts during 12 weeks of assessment in the field, which was comparable to the conventional fungicide Dithane M-45s, suggesting

that application of extracts produced from well-matured compost fortified with biocontrol agents could be an alternative control

strategy.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: Compost extracts; Trichoderma harzianum; Choanephora cucurbitarum; Choanephora wet rot disease suppression; Biocontrol

1. Introduction

Okra (Abelmoschus esculentus L.) is an annual commer-cial fruit vegetable for small-scale rural farmers, grown ona limited area throughout Asia. Disease management is oneof the most important components in the productionsystem, since this crop is prone to many fungal diseases,such as wet rot, powdery mildew and wilt, causingsignificant losses in yield and quality. Chemical pesticideshave been used widely for the control of these diseases.Since okra is harvested every alternate day, the dependenceon chemical pesticides results in several ecological pro-blems (Parveen and Dhandapani, 2002). However, inrecent years as a result of growing concerns for healthhazards and environmental pollution, agricultural pro-grammes have been developed aimed at high productivity

e front matter r 2007 Elsevier Ltd. All rights reserved.

opro.2007.07.002

ing author.

ess: yasmeenwarsi@yahoo.com (Y. Siddiqui).

while ensuring conversion and utilization of naturalresources on a sustainable basis. Therefore, in addition toexisting disease management tools, new and interestingapproaches are being explored to suppress diseases throughnatural and more eco-friendly means to reduce the use ofsynthetic fungicides.The effectiveness of using composts for disease control,

particularly against fungal pathogens, has been studiedextensively (Weltzien, 1991; Hoitink et al., 1997). However,during the composting process biocontrol agents do notconsistently colonize the composts. One of the reasons isthat most biocontrol agents are destroyed by the thermo-philic phase during the composting process. They mustrecolonize composts during the curing process and thisdoes not always occur. Inoculation of mature compostswith biocontrol agents has improved the consistency ofcolonization as well as the spectrum of disease suppression.Isolates of several Trichoderma spp. can provide effectivecontrol of diseases, and even better control if applied in

ARTICLE IN PRESSY. Siddiqui et al. / Crop Protection 27 (2008) 385–390386

combination with any of several bacterial biocontrolagents (De Ceuster and Hoitink, 1999). These results haveled to further work using filtered water extracts of compost.The use of compost extracts enriched with biocontrolagents presents a simple, inexpensive and potentiallyeffective alternative means to manage pests and diseases,to improve soil fertility and to sustain productivity,particularly in intensive vegetable production systems(Abbasi et al., 2002). The biocontrol activity of compostextracts, therefore, could be enhanced by fortifying itwith plant nutrients or biocontrol inoculants such asTrichoderma spp. Trichoderma spp. alone or in combina-tions with other beneficial microorganisms has beendocumented as the most common and effective biocontrolagent for disease control in various host–pathogen systemsin vitro as well as in field trials (Singh, 1991; Elad andShtienberg, 1994; Ristaino et al., 1991; Jinantana, 1995;Ibrahim, 2005).

This study was carried out to determine the effects ofTrichoderma-fortified rice straw (RST) and empty fruitbunch of oil palm (EFB) compost extracts on severity ofChoanephora wet rot in okra production.

2. Materials and methods

2.1. Screening of Trichoderma isolates against Choanephora

cucurbitarum

A dual culture test based on lytic activity and competi-tion for substrates was used to determine the antagonisticpotential of 15 Trichoderma isolates obtained from3-month-old chicken-manure-treated RST and EFB com-post. The wet rot pathogen C. cucurbitarum was isolatedfrom infected okra flowers and fruits. A mycelial plug(5mm diameter) taken from the edge of a 3-d-old potatodextrose agar (PDA) culture of C. cucurbitarum wasinoculated 30mm from the periphery of the 90mm PDAplate and a mycelial plug (same size) of the test antagonistwas placed 30mm from the C. cucurbitarum plug. All thetest antagonistic pairings were incubated at 28720 1C andarranged in a completely randomized design (CRD) andreplicated six times. The ability of Trichoderma isolatesto inhibit the growth of C. cucurbitarum was assessedafter 5 d of co-incubation, by measuring the radius of theC. cucurbitarum colony in the direction towards theantagonist colony (R2). The results were later transformedinto percentage inhibition of radial growth (PIRG) inrelation to radial growth of the pathogen in the controlplate (R1), using the following formula (Jinantana andSariah, 1998):

PIRG ð%Þ ¼R1 � R2

R1� 100%,

where R1 is the radius of C. cucurbitarum colony in controlplates and R2 the radius of C. cucurbitarum colony in adual-culture plate.

2.2. Effect of Trichoderma-fortified compost extracts on

disease severity

A field plot of okra, 30� 25m, was used to study theeffect of Trichoderma-fortified compost extracts on wet rotseverity of okra at Universiti Putra Research Farm no. 10.Processed chicken manure (Avanti green) was applied at6 t ha�1 2 weeks before sowing (AVRDC Report, 1998).Ridges were prepared 300mm in height, 600mm in widthand 3m in length. Seeds were sown directly on the ridgeswith spacings of 300mm between the plants. To achieve themaximum stand, three–four seeds were sown per hole, andthinned to one plant per hole when plants were 50–60mmtall. No extra fertilizer was added and weeds around theplants were controlled manually.

2.3. Preparation of Trichoderma inoculum and compost

extracts

Isolates of Trichoderma harzianum were grown on PDA(Oxoid). The conidial suspension was prepared accordingto the method described by Sariah (1994). Ten millilitresof sterilized distilled water was added to a 5-d-oldculture of T. harzianum and the surface was scrapedlightly with a bent glass rod. The conidial suspensionobtained was centrifuged for 5min at 4000g and washedtwice with distilled water. The conidial counts wereadjusted to approximately 5� 104 conidiaml�1 using ahaemocytometer.The compost extracts were prepared from 3-month-old

chicken-manure-treated RST and EFB compost accordingto the method described by Brinton (1995) and Yasmeen(2006). Compost and tap water were mixed in the ratio of1:5, in polyethylene non-degradable containers with covers.The mixtures were supplied with aeration using aquariumpumps and were stirred once daily manually using awooden rod and left at ambient temperature. Subse-quently, the mixture was filtered through double-layeredcheese cloth after the desired duration of extraction. Theextraction lasted for 21 d with filtrations at intervals for 3 d.The filtered extracts were kept at 20–25 1C out of directsunlight. The extracts produced were then fortified withTrichoderma inoculum to give colony-forming unit (cfu)counts of 3� 107ml�1 at the time of spraying. Thesurfactant Tween 20s at 10ml l�1 was also added to theextracts prior to application to obtain a better coverage ofthe foliage during spraying. Two-week-old okra plantswere sprayed weekly until run-off with an equivalentvolume of 0.5 lm�2 using a backpack sprayer with thefollowing treatments: water (control) (T1), fungicideDithane M-45s at the rate of 2 g l�1 (T2), RST compostextract (T3) Trichoderma-fortified RST compost extract(T4), EFB compost extract (T5), Trichoderma-fortifiedEFB compost extract (T6) and an aqueous suspension ofTrichoderma (T7). Watering was carried out daily in themorning through sprinkler irrigation for 2 weeks, thensubsequently at 3 d intervals to ensure adequate moisture in

ARTICLE IN PRESS

0 1 3 6 8 11 12 13 14 15 16

Perc

enta

ge Inhib

itio

n (

%)

60

65

70

75

80

85

90

95

Trichoderma Isolates

2 4 5 7 9 10

Fig. 1. In vitro antagonistic activity of isolates of Trichoderma harzianum

obtained from composts prepared from rice straw (RST) and empty fruit

bunch of oil palm (EFB) against Choanephora cucurbitarum (n ¼ 6).

Vertical bars indicate standard error according to Tukey’s test (HSD) at

Pp0.05.

Y. Siddiqui et al. / Crop Protection 27 (2008) 385–390 387

the soil. Inoculation was carried out by placing okraplants naturally infected with Choanephora randomlybetween the ridges.

2.4. Assessment of wet rot severity

Development of Choanephora wet rot on okra wasrecorded at weekly intervals using a scale of 0–5, where0 ¼ healthy, 1 ¼ 1–5% of mature leaves with necrotic andchlorotic symptoms, 2 ¼ 6–15% of mature leaves withnecrotic and chlorotic symptoms, 3 ¼ 16–50% of youngshoots and stem with water soaked lesions, 4 ¼ 51–95%water-soaked lesions with abundant mycelial growth andfructification and 5 ¼ dead plant. Disease severity (DS)and disease severity index (DSI) were expressed accordingto the formula given by Tarig et al. (1998):

% DS ¼PðNumber of seedlings in that rating � Severity ratingÞ � 100

Total number of seedlings assessed�Highest scale,

DSI ¼PðNumber of seedlings in that rating� Severity ratingÞ

Total number of seedlings assessed.

Reduction in disease severity as a measure of theeffectiveness of treatments in suppressing disease progresswas expressed using the same data plotted as a diseaseprogress curve. Slopes of the curves were obtained basedon the formula given by Campbell and Madden (1990) bytransforming the disease severity data using the model(Logit) Y ¼ B1/(1+B2exp(�B3X)), where Y representeddisease severity in percentage, B1 represented the asymp-totic stabilization of the curve, B2 was related to the initialdisease, B3 was the rate of disease progress and X was days.This model was fitted to the severity values by non-linearregression analyses using sigma plot software (SPSS,Version 9.0, Systat Software Inc. (SSI), California, USA).

The experimental layout was a randomised complete blockdesign replicated three times. Each block consisted of sevenplots with 35 plants per plot. Eighteen plants from the centreof each plot were sampled and tagged leaving the borderplants to minimize the border effect. Statistical analyses wereperformed using SAS statistical software (Version 8.2). Allthe percentage data were subjected to loge transformation toimprove homogeneity of variances and results were expressedin percentage. Data were analysed by analyses of variance(ANOVA) and treatment means were compared usingTukey’s studentised range (HSD) at Pp0.05.

To check the reproducibility of data all experiments werecarried out at least twice. Since both experiments yieldedsimilar results, the data from both repeats were pooledbefore subjecting them to statistical analyses.

3. Results

3.1. In vitro screening for Trichoderma isolates effective

against C. cucurbitarum

A total of 15 isolates of Trichoderma were obtained fromRST and EFB composts and all were identified as

T. harzianum based on cultural and morphologicalcharacteristics (Rifai, 1969). The colonies grew rapidly,forming a smooth-surfaced, watery white mycelial matwhich soon became whitish-green and then dull green dueto production of conidia. The colonies possessed repeatedlybranched conidiophores in tufts with divergent, irregularlybent, flask-shaped phialides. The size of conidia rangedfrom 2.8 to 3.2� 2.5 to 2.8 mm and they were smoothwalled with a sub-globose shape.The dual-culture test revealed that all the T. harzianum

isolates inhibited radial mycelial growth of C. cucurbitarum,but efficiency varied. All isolates gave greater than80% inhibition of mycelial radial growth (PIRG) ofC. cucurbitarum, with the exception of isolates 1, 2, 13and 14, which gave considerably lower PIRGs of 69.19%,77.65%, 78.48% and 77.52%, respectively (Fig. 1). Isolate7 with the highest PIRG value of 91.13% was selected forthe fortification of the compost extracts in the subsequentstudies.

3.2. Effect of Trichoderma-fortified compost extracts on

disease severity

Disease severity was used as an indicator of theeffectiveness of the Trichoderma-fortified compost extractsin suppressing Choanephora wet rot on okra in the fieldtrial. Low disease severity indicated the presence of diseasesuppression. Disease severity was significantly higher(Pp0.05) in the control plants (T1) (63.93%) with adisease index score of 4, and lowest in plants treated withTrichoderma-fortified RST extracts (T4) (9.56%) with adisease index of 1. Dithane M-45s (T2), Trichoderma-

fortified EFB compost extracts (T6), RST (T3), EFB (T5)and an aqueous suspension of T. harzianum (T7) recorded

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disease severity values of 10.25%, 19.38%, 37.56%,53.11% and 56.36% with a disease index of 1, 1, 2, 3 and3, respectively, 12 weeks after inoculation (Fig. 2).

The progress of disease development was also evaluatedusing the area under the disease progress curve (AUDPC).Development of symptoms was delayed in plants receivingTrichoderma-fortified RST extract (T4) and fungicidalspray (T2), until week 12 and were more effective thanother treatments as seen by differences in AUDPCvalues. The AUDPC at 12 weeks was significantlyhigher (Pp0.05) for the control (T1) and lowest forTrichoderma-fortified RST extract (T4), followed byDithane M-45s (T2), Trichoderma-fortified EFB compostextract (T6), RST (T3), EFB (T5) and the aqueoussuspension of T. harzianum (T7) (Table 1).

Similarly, on plants that received Trichoderma-fortifiedRST compost extract (T4) there was an 85.04% reductionin infection, followed by Dithane M-45s (T2), Trichoderma-fortified EFB compost extracts (T6), RST (T3), EFB (T5)

1 10 11 12 13

Dis

ease S

everity

(%

)

0

10

20

30

40

50

60

70T1T2T3T4T5T6T7

2 3 4 5 6 7 8 9

Assesment Time (Weeks)

Fig. 2. Severity of Choanephora wet rot disease assessed in okra plants

treated with compost extracts at weekly intervals (n ¼ 3). Vertical bars

indicate standard error according to Tukey’s test (HSD) at Pp0.05.

Table 1

Area under disease progress curve (AUDPC), disease severity and percentage r

12 weeks

Treatment AUD

Water (control) (T1) 230.3

Dithane M-45s (T2) 19.3

Rice straw compost extract (T3) 74.0

Trichoderma-fortified rice straw compost extract (T4) 18.0

Empty fruit bunch compost extract (T5) 104.0

Trichoderma-fortified empty fruit bunch compost extract (T6) 38.8

Aqueous suspension of T. harzianum (T7) 215.2

Means in the same column with same letter are not significantly different (Pp0

and the aqueous suspension of T. harzianum (T7) withreductions of 83.96%, 69.98%, 41.24%, 16.92% and11.84%, respectively, compared with the control at theend of the experiment.The application of Trichoderma-fortified compost extracts

delayed the disease infection and gave similar performanceas fungicidal spray with no significant difference betweenthem (Table 1). In contrast, the plants that receivedonly RST, EFB extracts and the aqueous suspension ofT. harzianum are significantly lower (Pp0.05) and showedsymptoms as early as weeks 3 and 4. Initial symptomsappeared as small chlorotic patches on mature leaves,which later turned water-soaked and gave a blightedappearance. As the disease progressed, the young shootswilted and turned into brown to black rotten tissue masses.Under severe infection, the infected parts including theflowers and young pods were covered with silvery myceliaof C. cucurbitarum with dark purple pin heads. The resultsobtained from the second field trial represented similarpatterns in terms of disease severity and disease progress.The percentage differences amongst treatments betweentwo trials were not significant.

4. Discussion

T. harzianum has been shown to act as a mycoparasiteagainst a range of economically important aerial and soil-borne plant pathogens, being successfully used in the fieldand greenhouse (Chet, 1987). The mode of inhibition inmycelial growth of C. cucurbitarum could be through lyticactivity and competition. When the mycoparasite reachesthe host, its hyphae often coil around it or are attached to itby forming hook-like structures. After these interactions,the mycoparasite penetrates the host mycelium, apparentlyby partially degrading its cell wall (Jinantana and Sariah,1998; Ibrahim, 2005). The radial mycelial growth ofC. cucurbitarum was restricted within the contact area orinteraction zone, resulting in lysis and disintegration of themycelium cell wall. Martin and Loper (1999) reported thatTrichoderma spp. are early colonizers of substrates andreduce the activity of other fungi simply by substrate

eduction for Choanephora wet rot on okra treated with compost extracts at

PC (unit square) Disease severity (%) % Reduction

7a 63.93a 0e

2f 10.25e 83.96a

4d 37.56d 41.24b

7f 9.56e 85.04a

9c 53.71ab 16.92c

6e 19.38c 69.98ab

5b 56.36ab 11.84d

.05) according to Tukey’s test (HSD) on their transformed values (n ¼ 3).

ARTICLE IN PRESSY. Siddiqui et al. / Crop Protection 27 (2008) 385–390 389

occupation and depletion and this would concur with thepresent observations.

The effectiveness of compost and compost extractsagainst plant diseases caused by a wide range of pathogensand pests, including bacteria and fungi, have beendemonstrated in numerous studies (Hoitink et al., 1993;Scheuerell, 2003). Various studies related to biologicalcontrol of wilts and wet rots by suppressive composts havehelped to diminish the incidence of these diseases aroundthe world (Cotxarrera et al., 2002; Kavroulakis et al.,2005). Several biocontrol agents have been identified fromsoils with added compost, such as Trichoderma (Phae et al.,1990; Hoitink and Boehm, 1999). The suppression capacitycould be due to compost recolonization by effectivebiocontrol agents after peak heating occurred in thecomposting process (Phae et al., 1990).

Differences in the effectiveness between the treatmentsused as foliar sprays to suppress Choanephora wet rotmight have resulted from the interaction between theantagonist and the extracts, in concomitance with chemicaland physiochemical characteristics and the nutrient contentof the extracts in controlling wet rot of okra. Diseasecontrol in this study could be attributed to the beneficial/antagonistic microorganisms (Trichoderma), microbialby-products (metabolites), and plant nutrients and humicacids present in the respective compost extracts. Thebeneficial microorganisms compete with the pathogensfor infection sites, leaving limited space for pathogens toproliferate or to secrete secondary metabolites on the plantsurface, and also directly parasitize pathogens (Baker andCook, 1982; Stindt and Weltzien, 1990; Weltzien, 1991; Maet al., 2001). The accumulation of metabolites andantibiotics produced by beneficial microorganisms duringbrewing of compost extracts could also suppress plantpathogens and activate natural plant defence responses(Zhang et al., 1998).

In this study, aqueous extracts of well-compostedorganic materials have been shown to reduce diseaseseverity in okra plants, if applied prophylactically to plantsurfaces. It was reported that when primary leaves ofbarley were pre-treated with compost extract from horsemanure and then inoculated with conidia of powderymildew (Blumeria graminis), infection levels were reducedby an average of 55% (Weltzien and Ketterer, 1986; Buddeand Weltzien, 1988).

The effectiveness of unfortified RST and EFB extracts incontrolling Choanephora wet rot was less than that ofTrichoderma-fortified RST and EFB compost extracts.However, the consistent disease suppression in plantsreceiving aqueous suspensions of T. harzianum only ascompared with the control (water) suggests that theeffectiveness of the compost extract was due largely tothe antagonist population in the extracts. This confirms thehypothesis that compost extracts rich in antagonistpopulations can be used as a substitute for chemicalpesticides for the control of Choanephora wet rot on okraunder heavy infection pressure.

5. Conclusion

Application of antagonists to control plant diseases hasbeen mostly through soil amendment in which highquantities of antagonists are required. Foliar applicationof fortified compost extracts is an alternative method,which could improve the establishment and colonizationability of antagonists, especially in the phyllosphere. Thiswill enhance the effectiveness of disease control with theadded advantage of using small volumes of antagonistpreparations.

Acknowledgements

The authors are grateful to the Ministry of Science,Technology and Innovation, SC Fund (MOSTI) forresearch funding. Special thanks are also expressed toDr. Peter G. Alderson for valuable editorial comments.

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