ARTICLE IN PRESS

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doi:10.1016/j.cr

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scchun@konku1Present add

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tion, Suwon, K2These two a

Crop Protection 26 (2007) 162–168

www.elsevier.com/locate/cropro

The effect of spent mushroom sawdust compost mixes, calciumcyanamide and solarization on basal stem rot of the cactus Hylocereus

trigonus caused by Fusarium oxysporum

Hyo-Won Choia,1,2, Ill-Min Chunga,2, Mi Ho Sina, Yu Surk Kima, Jung-Bo Sima,Jin-Won Kimb, Ki Deok Kimc,�, Se-Chul Chuna,�

aDepartment of Molecular Biotechnology, College of Life and Environmental Sciences, Konkuk University, 1 Hwayang-dong,

Kwangjin-gu, Seoul 143-701, KoreabDepartment of Environmental Horticulture, University of Seoul, Seoul 130-743, Korea

cDivision of Bioscience and Technology, College of Life and Environmental Sciences, Korea University, Anam-dong, Sungbuk-gu, Seoul 136-713, Korea.

Received 31 August 2005; received in revised form 11 April 2006; accepted 14 April 2006

Abstract

A severe epidemic of basal stem rot of the cactus Hylocereus trigonus occurred in 2001, in greenhouses of Goyang City, South Korea,

possibly due to continuous cultivation in soil beds. Fusarium oxysporum was isolated and its pathogenicity was demonstrated.

Inoculation of mycelial plugs on stem disks of cactus showed brown discoloration. Inoculation of a spore suspension of F. oxysporum

(1.40� 104 or 1.24� 108 sporesml�1) on the underground basal stems of cactus plants, followed by incubation at 28 1C in a growth

chamber, led to the development of brown spots identical to the original symptoms after 3 months. The effect of amendment with spent

mushroom sawdust, calcium cyanamide, straw and solarization on the development of the disease was studied. In a greenhouse study,

amendment with spent mushroom sawdust compost to the disease-conducive soil reduced the disease incidence to 3–12%, as compared

to 44–59% with the unamended disease-conducive soil. Autoclaved spent mushroom sawdust compost did not reduce the disease

incidence. The bacterial (1.95� 1011 cfu g�1) and fungal population (9.50� 107 cfu g�1) of spent mushroom sawdust was significantly

higher than those (2.0� 109 cfu g�1 and 0.13� 105 g�1 for bacteria and fungi, respectively) of disease-conducive soil. Also, disease-

suppressive soil had a higher fungal population (1.25� 105 cfu g�1) compared to disease-conducive soil (0.13� 105 cfu g�1). This trend

was repeated in the second experiment. Solarization with and without calcium cyanamide of disease-conducive soil reduced effectively

pathogen population and disease development, resulting in 16–53% disease incidence, as compared to 81% in the untreated control. Rice

straw as an organic amendment did not have synergistic effect on disease control when it was used along with calcium cyanamide for

solarization. The results indicate that the control of basal stem rot with spent mushroom sawdust compost may be due to biological

activity, and that solarization with calcium cyanamide is a highly effective tool for controlling basal stem rot.

r 2006 Elsevier Ltd. All rights reserved.

Keywords: Basal stem rot; Biological control; Fusarium oxysporum; Spent mushroom sawdust compost; Soil solarization

e front matter r 2006 Elsevier Ltd. All rights reserved.

opro.2006.04.017

ing authors.

esses: kidkim@korea.ac.kr (K.D. Kim),

k.ac.kr (S.-C. Chun).

ress: Division of Plant Pathology, National Institute of

ience and Technology, Rural Development Administra-

wonsungu, Kyunggido 441-707, Korea.

uthors are equally contributed to this work.

1. Introduction

The production of grafted cacti in Korea amounts to60–70% of the grafted cacti that are sold worldwide(Korean Ministry of Agriculture, 1998). Hylocereus trigo-

nus is used as a basal plant for grafting to the cactusGymnocalycium mihanovichii var. friedrichii Werd. Basalstem rot is caused by Fusarium oxysporum thatheavily infects H. trigonus (Hyun et al., 2001). Grafted

ARTICLE IN PRESSH.-W. Choi et al. / Crop Protection 26 (2007) 162–168 163

G. mihanovichii var. friedrichii Werd. which gives variousbeautiful colours such as red or yellow, onto the top of thebasal stem of H. trigonus grows in the bed or ground soil ofgreenhouses for over 3 months for market. Basal stem rotof this cactus is also caused by Rhizoctonia solani (KoreanSociety of Plant Pathology, 2004). F. oxysporum generallycauses wilt by plugging xylem vessel and other diseases likedamping off and root rot (Burgess et al., 1994). This funguson H. trigonus causes brown lesions on underground stemsand eventually leads to rotting of the stem but not the root.Grafted cacti are cultivated year after year in bed soil ingreenhouses without crop rotation. Because of thiscontinuous cultivation, the incidence of basal stem rothas been increasing. In an attempt to control this problem,farmers change the bed soil once per year, which results inincreased labour and production costs. Hyun et al. (2001)reported disease incidences of 42% and 82% after 3 and 5consecutive years of cultivation, respectively.

The amendment of a mineral soil in a field microplotwith spent mushroom compost significantly increased thetuber weight of potatoes after inoculation with thepathogens Verticillium dahliae and/or Pratylenchus pene-

trans, the causal agents of early dying of potato (LaMondiaet al., 1999). Also, seedling damping-off of cucumber couldbe significantly reduced by the amendments of differentspent mushroom composts such as sawdust and cotton gin,resulting in 29% seedling damping-off compared to62–67% disease incidence of the unamended control (Sin,2002).

Calcium cyanamide, which is mainly used as a fertilizerhas been used as a soil fungicide against F. oxysporum f.sp.pisi (Lo and Lin, 1989), against Sclerotinia sclerotiorum

(Milinko et al., 1989), in cabbage (Gabrielson et al., 1973),in garden peas (Jones and Gray, 1973), in beans and greencucumber (Mattusch, 1984). The fungicidal effect of thisdisinfestant is based on its metabolizing cyanamide,guanidine and bicynamide (Bourbos and Skoudridakis,1993). It is not toxic to fish and bees, and does not leaveresidues in the soil (Royal Society of Chemistry, 1984). Inaddition, combination of solarization with organic matter,nitrate or ammonium-N fertilizer or with calcium cyana-mide controlled to a satisfactory degree other soil-bornediseases on other cultivated plants (Stapleton et al., 1991;Horiuchi, 1991; Gamliel and Stapleton, 1993; Bourbos andSkoudridakis, 1993). Bourbos and Skoudridakis (1993)reported that the use of calcium cyanamide in combinationwith 3 weeks solarization and organic matter was of specialpractical interest, because only 3 weeks solarization wasrequired, allowing this method to be used in a greenhouseeven when one crop succeeded the other after a shortperiod of time.

Solarization with polypropylene vinyl (Bourbos et al.,1997; Song and Kang, 2000) has been effective in managingplant disease. Mulching with clear vinyl raised the soiltemperature to 54 1C at a depth of 5 cm, and to 44 1C at adepth of 10 cm, resulting in the control of potato scab(Song and Kang, 2000).

The objectives of this study were to confirm the causalagent of basal stem rot of cactus in vivo, and to determinethe effect of spent mushroom sawdust compost, rice straw,suppressive soil, calcium cyanamide and soil solarizationon the development of basal stem rot of cactus in thegreenhouse.

2. Materials and methods

2.1. Isolation of F. oxysporum

Cactus plants showing basal stem rot were collectedfrom five greenhouses in Koyang city of Kyunggi Province,Korea. Diseased parts were cut into pieces of 5� 5mm2,surface sterilized in 1% sodium hypochlorite for 30 s, andrinsed well with sterile distilled water. The sections wereplated on water agar and incubated at 28 1C. The myceliumthat grew subsequently was transferred onto potatodextrose agar (PDA, Becton, Dickinson and Co., Sparks,MD, USA) and potato carrot agar (Hyun et al., 1998), andidentified according to Nelson et al. (1983). The isolationfrequencies from pieces of cactus with early and latesymptoms were determined.

2.2. Pathogenicity test in stem disks and growth chamber

Mycelial plugs (2mm� 2mm) of isolates identified as F.

oxysporum were inoculated on the stem disks placed on themoisturized sterile filter paper in the Petri dish plates andcovered with lids. The inoculated cactus disks wereincubated at 30/25 1C in a growth chamber (light,10,000Lx/dark, 12 h/12 h) with 70% RH until brownlesions appeared. The control was water agar only laidon the surface of stem disks of cactus. There were 64isolates of F. oxysporum and four stem disks per isolatewere inoculated.The F. oxysporum isolate, 01101, which caused strong

brown lesions on stem disks was incubated on PDA at28 1C for 5 d. The plates were then filled with 5ml of steriledistilled water and scraped with a sterile transfer loop toharvest the conidia. The resulting spore suspension wasfiltered through two layers of sterile cheesecloth. The sporeconcentrations were adjusted to approximately 1.24� 108

and 1.4� 104 conidiaml�1, and Tween 80 was added to afinal concentration of 0.5%.

2.3. Amendment with spent mushroom sawdust media and

suppressive soil

Disease-conducive (sandy loam soil) which resulted in a90% basal stem rot infection was used to determine theeffect of spent mushroom sawdust media on diseasedevelopment. Containers of 25� 16� 10 cm3 were filledwith the following six mixtures; (1) disease-conducive soil:3-d-old spent mushroom sawdust:rice hulls ¼ 7:4:1 ratio, (2)disease-conducive soil:7-d-old spent mushroom sawdus-t:rice hulls ¼ 7:4:1, (3) disease-conducive soil:autoclaved

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spent mushroom sawdust: rice hulls ¼ 7:4:1, (4) disease-conducive soil:suppressive soil ¼ 1:1, (5) disease-conducivesoil:autoclaved suppressive soil ¼ 1:1, (6) disease-condu-cive soil: rice hull ¼ 11:1.

In the repeat experiment, the above treatments were somodified that the treatment ‘‘disease-conducive soil only’’was included as the control, compared to ‘‘disease-conducive soil:rice hull’’. In addition, the mix ratio ofspent mushroom sawdust was modified. Also, the effect ofdisease-suppressive soil on disease incidence was not testedin the repeat experiment because that treatment was notreally necessary for the present study. However, we tried todetermine the microbial population of the disease-suppres-sive and conducive soil obtained from the same grower’sgreenhouse bed soil. The treatments were: (1) disease-conducive soil only, (2) disease-conducive soil:ricehull ¼ 9:1 ratio, (3) disease-conducive soil:spent mushroomsawdust:rice hulls ¼ 7:2:1 ratio, (4) disease-conducive soil:autoclaved spent mushroom sawdust: rice hulls ¼ 7:2:1, (5)disease-conducive soil:spent mushroom sawdust ¼ 4:1 ra-tio, (6) disease-conducive soil:autoclaved spent mushroomsawdust ¼ 4:1 ratio.

Spent mushroom sawdust is the medium used in oystermushroom growth beds at the National Agricultural andTechnology Institute of the Rural Development Adminis-tration of South Korea. The soil and spent mushroomsawdust media were autoclaved for 40min each for 2consecutive days. The cacti were watered after 3 weeks,about the time when roots began to develop. Thepercentage infected cacti was determined 2 months afterthe plants were first watered. There were four replicationsper treatment with eight plants per replication. Thetreatments were arranged with a completely randomizedblock design.

2.4. Microbial populations in disease-suppressive, conducive

soil and spent mushroom sawdust

The samples of disease-suppressive and disease-condu-cive soil from the three locations of the cactus-growing soilbed were taken. Ten grams of the soil was mixed with 90mlof sterile distilled water and shaken for 30min at 250 rpmon a rotary shaker. Serial dilutions to 10�9 were preparedand 1ml of each dilution spread onto one-third strengthPDA to determine the fungal population, on nutrient agar(NA) (Becton, Dickinson and Co., Sparks, M.D., USA) todetermine the bacterial population, and on actinomycetesisolation agar (Becton, Dickinson and Co., Sparks, M.D.,USA) to determine the actinomycetes population. Therewere three samples per soil type and two replicates perdilution.

2.5. Effect of soil solarization on disease development

Four containers (25� 16� 10 cm3) (width� length�height) per treatment filled with disease-conducive soilwere saturated with water and covered with polyethylene

vinyl in a greenhouse. Four treatments were established: (1)disease-conducive soil, (2) disease-conducive soil withcalcium cyanamide (20 gm�2 to a dept of 5 cm), (3)disease-conducive soil with rice straw (200 gm�2 to adepth of 5 cm) shredded to 0.5–1 cm, and (4) disease-conducive soil with rice straw and calcium cyanamide as asame proportion described in the previous treatments. Ricestraw was added into disease-conducive soil on anassumption that increased microbial activity and respira-tion during solarization due to the organic amendmentcould reduce on the pathogen population. Non-solarizedrice straw was included as the control for the solarized ricestraw. The soils were solarized for 6 weeks from August toSeptember 2002 in a closed greenhouse. The soil tempera-ture during the solarization period reached 40–45 1C at5 cm depth. After soil samples were collected to analyze thepopulations of F. oxysporum, grafted cacti were planted.The cacti were watered after 3 weeks, about the time whenroots began to develop. The number of cacti showingbrown spots was determined 2 months after the plants werefirst watered as previously described. There were fourreplications per treatment with eight plants per replication.Treatments were arranged with a completely randomizedblock design.For the study on F. oxysporum population in solarized

soils, 10-g samples of soil, three samples per container werepassed through a 2-mm pore size sieve and mixed into90ml of sterile distilled water. Erlenmeyer flasks containingthe soil suspensions were shaken for 24 h at 150 rpm on arotary shaker. To determine the colony forming units(CFU) of F. oxysporum per gram of soil, 1ml each ofdilutions of 100–10�1, two plates per dilution were platedonto Komada media (1975) and the plates were incubatedat 28 1C for 10 d.

2.6. Statistical analysis

All experiments were conducted at least twice, with fourreplications per treatment, although some experimentswere not necessarily exactly duplicated because of differ-ences in inoculum concentration, amount of amendmentsand sampling times. Therefore, data sets could not bereadily combined or presented as two separate columnsacross experiments. However, data sets for ‘‘amendmentwith spent mushroom sawdust’’ were presented as exp. 1and exp. 2 because we considered that they were the mostcritical experiment in the present study. Also, there weresmall differences among experiments in disease incidenceand microbial population in the experimental controls,although all trends were confirmed in each repetition.Results were analyzed by ANOVA and the pooled meanvalues were separated on the basis of least significantdifference with SigmaStat software (Systat Software, Inc.,Point Richmond, CA, USA). Also, for the microbialpopulation study, the data were log-transformed beforestatistical analysis. In addition, statistical analysis on

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Table 1

Rate of incidence of basal stem rot of Hylocereus trigonus caused by

Fusarium oxysporum inoculated at different concentrations

Treatments (conidia ml�1) Disease incidence (%)

Uninoculated 6bz

1.40� 104 63a

1.24� 108 72a

zMeans followed by same letters within a column are not significantly

different (LSD, Po0.05).

Table 2

Effects of amendment with spent sawdust mushroom media on the

incidence of basal stem rot of Hylocereus trigonus

Treatmenty Disease incidence (%)

Exp. 1 Exp. 2

A:FSM:rice hull (7:4:1) 6bz

A:OSM:rice hull (7:4:1) 3b

A:SS (1:1) 3b

A:autoclaved soil (1:1) 31a

A:ASM:rice hull (7:4:1) 25a

A:rice hull (11:1) 44a

A2 only 59a

A2:rice hull (9:1) 43a

A2:FSM2:rice hull (7:2:1) 28bc

A2:AFSM2:rice hull (7:2:1) 39ab

A2:FSM2 (4:1) 12c

A2:AFSM2 (4:1) 37ab

yA, disease-conducive soil; FSM, fresh spent mushroom sawdust media

(3 d after being spent); OSM, old spent mushroom sawdust media (7 d

after being spent); SS, suppressive soil; AFSM, autoclaved fresh spent

mushroom sawdust media. A2, disease-conducive soil at second experi-

ment, FSM2, fresh spent mushroom sawdust media at second experiment;

AFSM, autoclaved fresh spent mushroom sawdust media at second

experiment.zMeans followed by same letters within a column are not significantly

different (LSD, Po0.05).

H.-W. Choi et al. / Crop Protection 26 (2007) 162–168 165

disease incidence was conducted with arcsine-transformeddata.

3. Results

3.1. Symptoms and isolation of F. oxysporum

Early symptoms comprised small brown spots, afterwhich soft rot appeared (Fig. 1A and B). Fungi wereisolated from plants showing symptoms. Of the 110 isolatescollected, 64 were identified as F. oxysporum according toNelson et al. (1983). Of these 64 isolates, 62% were isolatedfrom tissues with early symptoms and 48% from tissueswith soft rot. The remaining isolates were identified asTrichoderma, Alternaria, and Aspergillus species.

3.2. Pathogenicity tests

Of the 64 isolates, 10 were tested for pathogenicity invitro. Each of these isolates caused brown spots on thesurfaces of cactus disks. One isolate (F. oxysporum 01144)was tested for pathogenicity in vivo, and caused smallbrown spots 3 months later on the underground basalportion of cacti grown in soil in a growth chamber. Thedisease incidences were 63% and 72% after inoculation ofbasal cactus stems with solutions of 1.4� 104 or1.24� 108 cfuml�1, respectively (Table 1) and were notstatistically different (LSD, P ¼ 0.05). The uninoculatedcontrol had 6% disease incidence.

3.3. Use of spent mushroom sawdust to control basal stem

rot

Treatments with spent mushroom sawdust significantlyreduced the development of basal stem rot, resulting in 6%and 3% disease incidences for 3-d-old spent mushroomsawdust and 7-d-old spent mushroom sawdust, respec-tively, as compared to a 44% disease incidence for thecontrol. Amendment with suppressive soil that showed nodisease incidence reduced the disease incidence to 3%. Incontrast, autoclaved suppressive soil and autoclaved fresh

Fig. 1. Symptom of brown spot (A) and rot (B) of basal stem caused by Fu

healthy.

spent mushroom sawdust did not reduce disease incidencewhen mixed with disease-conducive soil, with 31% and25% disease incidence, respectively, similar to the disease-conducive soil (Table 2).

sarium oxysporum. (A) Left, healthy; right, diseased. (B) Left, rot; right,

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Table 5

Control efficacies of calcium cyanamide, rice straw and soil solarization on

the basal stem rot of Hylocereus trigonus

Treatmenty Disease incidence (%)

Control 81az

Solarization 38b

Rice straw 53b

Solarization+calcium cyanamide 16c

Solarization+rice straw 44b

Solarization+rice straw+calcium cyanamide 19c

yThe solarization period was 6 weeks, the volume of rice straw was

200 gm�2 to the 5 cm depth, and the volume of calcium cyanamide was

20 gm�2 to the 5 cm depth.zMeans followed by same letters within a column are not significantly

different (LSD, Po0.05).

H.-W. Choi et al. / Crop Protection 26 (2007) 162–168166

3.4. Microbial populations in disease-conducive, suppressive

soil, and spent mushroom sawdust

The bacterial, actinomycetes, and fungal populations ofthe disease-conducive soil were 2.04� 109, 3.0� 109, and0.13� 105, respectively (Table 3). Those from suppressivesoil were 1.26� 109, 1.3� 104, and 1.25� 105, respectively.Fungal population was significantly higher in suppressivesoil than disease-conducive soil. However, bacterial andactinomycetes populations were significantly higher indisease-conducive soil than disease suppressive soil. Spentsawdust from mushroom growth medium had significantlyhigher fungal and bacterial populations compared to thoseof disease-conducive and suppressive soil (Table 3). Incontrast, actinomycetes were not detectable at 102 g�1 ofcompost.

3.5. Effect of soil solarization on basal stem rot development

Solarization with or without the addition of rice straw,and with or without calcium cynamide reduced population(cfu g�1 soil) of F. oxysporum to 42–63% as compared withbefore solarization. Addition of rice straw during solariza-tion did not affect the F. oxysporum population. However,

Table 3

Microbial populations of conducive and suppressive soil and spent sawdust m

Treatment Population of microorganisms/g soil or c

Bacteria (109) A

Exp. 1 Exp. 2 E

Conducive soilw 2.04by 1.42b 3

Suppressive soilx 1.26c 0.013c 1

Spent sawdust compost 195a 3.28a —

wConducive soil is from a greenhouse soil bed that showed 90% disease incxSuppressive soil is from which cacti had been cultivated for 3 consecutive ye

less than 5–7%) according to the farmer.yMeans followed by same letters within a column are not significantly diffezActinomycete was not detectable at 102 level per gram of compost or both

Table 4

Effects of calcium cyanamide, rice straw, and soil solarization on the soil pop

Treatmentx Population o

Pre-y

Control 8.8

Solarization

Solarization+rice straw

Solarization+calcium cyanamide

Solarization+rice straw+calcium cyanamide

xThe solarization period was six weeks, the volume of organic matter was

20 gm�2 to a depth of 5 cm.yPre-, before soil covering; post-, after uncovering the soil; change, change in

sources for the control and all solarization treatments were the same.zMeans followed by same letters within a column are not significantly differe

treatment population of the control.

it appeared that calcium cyanamide had a synergistic effectduring solarization on reduction of the F. oxysporum

population (Table 4).Solarization with or without the addition of rice straw

reduced the disease incidence significantly, to 16–53%, ascompared with 81% for the untreated control (LSD,P ¼ 0.05) (Table 5). However, solarization combined withrice straw did not reduce the disease incidence to a

edium

ompost

ctinomycetes (104) Fungi (105)

xp. 1 Exp. 2 Exp. 1 Exp. 2

.0a — 0.13c 1.70c

.3b — 1.25b 32.7bz — 950a 210.0a

idence.

ars in the farmer’s greenhouse but disease incidence was very low (possibly

rent (LSD, Po0.05).

soil.

ulation of Fusarium oxysporum

f F. oxysporum (� 105CFU)/g soil

Post-y Change (%)

9.4az +6.8d

2.7c �62.5b

5.2b �43.5c

0.5d �94.3a

5.1b �42.0c

200 gm�2 to a dept of 5 cm, and the volume of calcium cyanamide was

the population from the pre-treatment to the end of the treatment. The soil

nt (LSD, Po0.05). The percent changes were calculated based on the pre-

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significantly greater extent than did solarization or ricestraw alone. In contrast, the addition of calcium cyanamidewith and without rice straw during solarization led tosignificantly lower disease incidence (19% and 16%),compared to the disease incidence of 38% after solarizationalone (Table 5).

4. Discussion

Brown spots occurred on the basal stems of cacti, grownin a growth chamber 3 months after inoculation with aspore suspension by immersing the surface of the basalstem before planting, and F. oxysporum could be re-isolated from these stems, indicating that the basal stem rotwas caused by F. oxysporum. Uninoculated cacti alsoshowed brown spots at the low frequency of 6%, comparedwith the 63–72% in inoculated plants. It is thought thatwounding during the planting process causes the brownspots in the control. Under ideal conditions, cacti exhibitbrown spots 1 month after planting in an infested field. InKorea, this disease develops most often from Novemberthrough April in the greenhouse, which is usuallytemperature-controlled to remain above 15 1C at nightand between 30 and 40 1C during the day.

The suppressive soil, applied as an amendment, whichoriginated from the farmer’s greenhouse was said to havealmost 0% disease incidence according to the growerduring his cultivation, but we observed roughly less than5–7%, even after three years of continuous monoculturewith cacti. The suppressive soil (sandy loam) had a pH 7.6,total nitrogen 1053 mg g�1, phosphate 332 mg g�1, potas-sium 0.98 cmol kg�1, Ca 5.2 cmol�1kg, Mg 1.1 cmol kg�1,electric conductivity (EC) 3.9 ds cm�1. The disease-con-ducive soil (sandy loam) from another farmer’s greenhousehad pH 5.9, total nitrogen 1,250 mg g�1, phosphate490 mg g�1, potassium 1.83 cmol kg�1, Ca 9.0 cmol kg�1,Mg 5.4 cmol kg�1, EC 11.1 ds cm�1. The farmer had growncactus for more than 3 years and disease incidence was veryhigh. Nutrient status and EC of cacti-growing soil variedgreatly depending on the growers but there was nosignificant correlation between EC or soil pH and diseaseincidence (Chun, 2002).

Amendments of suppressive soil, fresh spent mushroomsawdust compost or old spent mushroom sawdust compostinto disease-conducive soil resulted in significant diseasereduction, as compared to amendment of autoclaved soilinto disease-conducive soil. The disease incidences werehigher than 25% for disease-conducive soil amended withautoclaved suppressive soil or autoclaved spent mushroomsawdust compost, indicating that the reduction in diseaseincidence might be due to a biological function. Thebacterial and actinomycetes populations in the disease-conducive soil were significantly higher than those insuppressive soil, but the fungal population was significantlylower, implying that the reduction in the disease incidencemight be due to the increased population of fungi, asopposed to bacteria or actinomycetes. Trichoderma species

were readily isolated from PDA plates spread withsuspensions of suppressive soil (approximately 47% of 75colonies from one plate). We did not identify every colonyof all replicates of the PDA plates.The disease-reducing properties of suppressive soil have

been well documented (Cook and Baker, 1983; Cook,1993). Treatment with natural disease-suppressive soilresulted in reduced damage to susceptible plants over yearsof treatment and this suppressive property was due tomicrobial antagonists (Cook and Baker, 1983; Cook,1993).All spent mushroom sawdust compost produced in

Korea is discarded. This compost could be recycled foragricultural use, with great potential benefit and very lowcost. Compost-amended soil has been reported to suppressplant diseases caused by nematodes, bacteria, or soil-bornefungi in various crops (Hoitink and Fahy, 1986). Increasingamounts of organic matter are often correlated withincreased disease suppression (Craft and Nelson, 1996;Inbar et al., 1991; Kuter et al., 1988), and microbial activityhas been used as an indicator of the disease-suppressiveproperties of compost against Pythium spp. (Boem andHoitink, 1992; Chen, et al., 1988a, b). Postma et al. (2003)also reported that relatively conducive sandy–potting soilmixture and the potting soil could be more suppressiveby adding compost products of different origin andmaturation.Soil solarization alone significantly reduced the incidence

of basal stem rot, as compared to the situation withuntreated disease-conducive soil. However, no significantdisease reduction resulted from the amendment of ricestraw into disease-conducive soil followed by solarization,compared to solarization alone, indicating that there wasno synergistic effect of the amendment of rice straw duringsolarization. Bourbos et al. (1997) reported that use ofcalcium cyanamide with 6 weeks solarization and organicmatter significantly reduced infected plants to 2.4%compared to use of calcium cyanamide without organicmatter with solarization where 8.8% plants were infected.However, in our study, there was no difference betweenthese two treatments. We do not know what made thisdifference but it may be due to a difference between the twoorganic amendments or to the effect of solarization on therice straw amendment. Bourbos et al. (1997) did notmention what organic matter was used in their study.In contrast, the amendment of calcium cyanamide into

disease-conducive soil followed by solarization significantlyreduced disease incidence, as compared to solarizationalone, suggesting that calcium cyanamide might reducesynergistically the disease incidence caused by F. oxyspor-

um (Klasse, 2002). Calcium cyanamide was widely used inthe twentieth century, although its usage has subsequentlydeclined, owing to several newly developed chemicalcompounds (Cornforth, 1971). Calcium cyanamide, anitrogen fertilizer containing 20–24% nitrogen,, couldoffer a second benefit, as an effective pesticide againstsoil-borne fungi (Klasse, 2002).

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The present study suggests that spent mushroomsawdust and solarization with calcium cyanamide may beutilized for the control of basal stem rot of the cactus. Wespeculate that spent mushroom sawdust may have antag-onistic fungal populations against F. oxysporum. It wouldbe interesting to isolate the antagonists and test themagainst plant pathogens. Spent mushroom sawdust couldbe a potential substrate for antagonists to maintain properpopulation of antagonists to control plant disease. Thisassumption would be tested in future work.

Acknowledgments

This study was supported in part by the research fund ofKonkuk University and Institute of Kyunggido Agricul-tural Technology in 2002.

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