SUPPRESSIONOF PLANT DISEASES BY COMPOSTS
H. A. J. Hoitink, A. G. Stone and D. Y. Han
ProfessorandGraduateResearchAssociates,Departmentof Plant Pathology,Ohio Agricult
Researchand DevelopmentCenter,The Ohio StateUniversity, Wooster,OH 44691
1. ABSTRACT
2. INTRODUCTION
Compostsoffer unique opportunitiesto examinefundamentalinteractionsbetweenplant pathogens,biocontrol
agents,soil organicmatter,andplant roots. Theseorganic
amendmentshavethe potentialto provide consistentbiological control of manyplant diseases.Foliar, vascularas
well asroot pathogensmaybe affectedby composts.Many
factorsinfluencethesebeneficialeffects. For example,the
compositionof the feedstockused in the preparationof
compostsaffectsthepotentialfor biological control aswell
asthe microflora active in control. Heatgeneratedduring
compostingkills or inactivatespathogensif the processis
monitoredproperly.Unfortunately,biocontrol agentswith
the exceptionof Bacillus spp. are also killed. Therefore
this beneficialmicrofloramustlargelyrecolonizecomposts
after peakheating. The compostingenvironmentandconditions during curing and utilization also affect the potential for recolonizationof compostsby biocontrol agents
andthe inductionof diseasesuppression.In practice,controlled inoculationof compostwith biocontrol agentshas
During the 1960's,nurserymenacrossthe United States
explored the possibility of using compostedtree bark as
peatsubstitutesto reducepotting mix costs. Early during
the utilization of bark composts,improved plant growth
anddecreased
lossescausedby Phytophthoraroot rotswere
observedassidebenefitsin the nurseryindustry. Today it
is recognizedthat control of suchroot rots with composts
canbe aseffectiveasthat obtainedwith fungicides (Hardy
andSivasithamparam,1991; Hoitink et al., 1991;Ownley
and Benson, 1991). Therefore,the ornamentalplant industry relies heavily on compostproductsfor control of
diseasescausedby thesesoilborneplant pathogens.Composts have replaced methyl bromide in this industry
(Quarles and Grossman,1995). In field applicationsof
compostssimilar resultshavebeenobtained(Hoitink and
Fahy, 1986; Lumsdenet al., 1983, SchUleret al., 1993).
Examplesof diseasescontrolledby compostsarereviewed
in Hoitink and Fahy, 1986.
.
suppression.
.
.
.
crops,particularly If usedm containermedia(Inbar et al.,
1993). The rateof respirationis oneof severalprocedures
that can be usedto monitor stability of composts(Iannotti
et al., 1994). Variability in compoststability is one of the
principal factorslimiting its widespreadutilization. Maturity is lessimportant in ground bed or field agricultureas
long asthe compostis appliedsufficiently aheadof planting to allow for additional stabilization;however, lack of
maturity frequentlycausesproblemshereaswell.
.
. Effectsof.chemlcalpropertiesof comp~stson.soilb~~e
diseaseseventyo.ftenare~verlooked(reviewedm Holtlnk
et al., 1991). Highly salIne compostsenhancePythium
andPhytophthoradiseasesunlessthey areappliedmonths
proved necessary to induce consistent levels of disease
.
,i-'
..
I-
Stability of compostsmustbe consideredin biological
control. Immaturecompostsserveas food for pathogens.
Their populationsincreasein freshorganicmatterandcause
diseaseevenif colonizedby biocontrolagents.On the other
hand,biocontrol agentsinhibit or kill pathogensin mature
composts and thereby induce disease suppression.
Biocontrol agentsin compostsmay induce systemicacquired resistanceto foliar plant pathogens.Finally, excessively stabilizedorganicmatterdoesnot supportthe activity ofbiocontrol agents.Microorganismsincapableof providing biological control predominatehere. Diseasedevelopson plantsproducedin suchhighly mineralizedorganicmatter
.
Physicaland chemical propertiesof compostsaffect
biol~gical con.trol.Salinity and the rat~ of releaseof plant
nutnents,particularlythe amountof mtrogenreleased,affect suppressiveness.
CompostpH andtiming of compost
applicationrelativeto plantingof cropsareother factorsto
be considered.In summary,the field is very complex.
...
Composts must be of consistent quality to be used successfully in biological control of diseases of horticultural
ahead of planting to allow for leaching. Compost prepared
from municipal sewagesludgehavea low carbonto nitrogen ratio. They releaseconsiderableamountsof nitrogen
and enhanceFusarium wilt (Hoitink et al., 1987). On the
otherhand,compostsfrom high C/N materials,suchastree
barks,immobilizenitrogenandsuppressFusariumdiseases
if colonizedby an appropriatemicroflora (Trillas-Gay et
al., 1986). High amonium and low nitrate nutrition increases
X CongresoNacional Agronomico 1111Congresode Fitopatologia 1996
47
I
;
'
-;
-
Suppressionof plant diseasesby...
,
'
Fusarlum
.
Wi' Its (Sc hnei' der, 1985), Perhaps the low in C/
N redominantly ammonium-nitrogen-releasingsludge
P st enhancesFusarium diseasesfor this reason,
compo
3. FATE OF BIOCONTROL AGENTS
DURING
COMPO STING
.
.,.
The composting process is ofte? divided mto three
phases,The initial phaseoccursdurmg the fiTst24-48 hr
astemperaturesgradually rise to 40-50 C, and sugarsand
other easily biodegradablesu~stances
are destroyed,During the secondphase,when high tem~eraturesof 55- 70 C
prevail, lessbiodegradablecellulosIc substanc~sare destroyed. Thermophilic microorgansimspredommateduring this part of the process.Plantpathogensand seedsare
killed by the heatgeneratedduring this high phase(Bollen
1993; Farrell 1993), Compostpiles must be turned frequently to exposeall partsto high temperatureto produce.
a homogeneous
productfree of pathogensandweedseeds,
Unfortunately, most beneficial microorganismsalso are
killed during the high temperaturephase
of composting.
'"
Curing begins as the concentration of readily blode-
gradablecomponentsin wastesdeclines,As a result, rates
of decomposition,heatoutput and temperaturesdecrease,
At this time, mesophilicmicroorganismsthat grow at temperatures<40 C recolonizethe compostfrom the outer low
temperaturelayerinto the compostwindro~ or pil,e,Therefore, suppressionof pathogensand/or diseaseIS largely
inducedduring curing, becausem~stbiocontrol agentsrecolonizecompostsafter peakheatingalso.
Bacillus spp" Enterobacter spp" Flavobacterium
balustinum,Pseudomonasspp" otherbacterialgeneraan~
Streptomycesspp" aswell asPenicillium spp" sever~lTrlchodermaspp" Gliocladium virens and other fungi have
beenidentified as biocontrol agentsin compost-amended
sustrates(ChungandHoitink1990; HadarandGorodecki,
1991;Hardy andSivasithamparam
1991;Hoitink and,Fahy
1986;Nelsonetal., 1983;Phaeet al., 1990), The moisture
contentof compostcritically affectsthe potential for bacterial mesophilesto colonizethe substrateafter peakheating, Dry composts«34% moisture,w/w) be~omecolonized by fungi and are conduciveto Pythium diseases,In
order to induce-suppression,
the moisturecontentmust be
high enough(at least40-50%,w/w) sothat bacteriaaswell
as fungi colonize the substrateafter peak heating. Water
must often be addedto compostsduring compostingand
curing to avoid the dry condition. CompostpH also affectsthe potential for beneficial bacteriato colonize composts, A pH <5.0 inhibits bacterial biocontrol agents
(Hoitink et ai" 1991).
,
dampi'
"
, samecompostproducedin a partonia
diseasesthan the
tially enclosedfaciltty were
h
fiew micro
'
b ia
' I species
'
survive heat treatment(Kuter et al., 1983), Compostpr~duced in the opennear a forest (field compost),an enVi-
ronmentthatishigh in microbial speciesdiversity, iscolonized by a greatervariety of biocontrol agentsthan the
sameproducedin an in-vesselsystem(Kuter et al., 1983),
Frequently,however,Rhizoctoniaand other diseasesare
observedfor sometime after compostsare fiTst applied
(Kuter et al., 1988; Lumsden et al., 1983). Three approachescanbeusedto solvethis problem:Curingof compostsfor four monthsor morerenderscompostsmoreconsistentlysuppressive(Kuter et al., 1988). The secondapproach is to incorporatecompostsino field soils for several monthsbeforeplanting (Lumsdenet ai" 1983), The
third approach is to inoculate composts with specific
biocontrol agents(K wok et ai" 1987),
.
A specific strain of Flavobacterium balust~num,
and
an is~lateof Tric~odermahamatumhave ~eenide,ntified
that
mduce
levelsofofplant
suppression
to If,di~eases
caused
by a consistent
broad spectrum
pathogens,
moculated into compost after peak heating, but before signifi-
cant levelsof recolonizationhaveoccurred, Patentshave
beenissuedto The Ohio StateUniversity for this process
(Hoitink, 1990). In Japan,Phaeet al. (1990), isolateda
Bacillus strainthat inducespredictablebiological control
in composts,It hasbeenrecognizedfor decadesthat single
strainsare not as effective in biological control in field
applications as mixtures of microorganisms, (Garrett,
1955). The sameappliesto containermedia(Kwok et ai"
1987),
4. MECHANISMS OF SUPPRESSIONIN
COMPOSTS
Two classesof biological control mechanismsknown
as "general" and "specific" suppressionhave been describedfor compost-amended
substrates,Themechanisms
involved arebasedon competition,antibiosis,hyperparasitism and the induction of systemicacquiredresistance
in the host plant. Propagulesof plant pathogenssuchas
Pythium and Phytophthoraspp., are suppressedthrough
the "general suppression"phenomenon(Boehm et ai"
1993;Chen et ai" 1988a;Chen et al., 1988b;Cook and
Baker 1983; Hardy and Sivasithamparam 1991;
Mandelbaumand Hadar 1990), Many types of microorganisms present in compost-amendedcontainer media
function as biocontrol agentsagainstdiseasescausedby
PhytophthoraandPythiumspp,(Boehmet ai" 1993;Hardy
and Sivasithamparam1991), Propagulesof thesepatho.,
gens,if inadvertentlyintroducedinto compost-~ended
'
t '
Variability in suppression 0fRh IZOC
ng -,off
oma
'
d '
andFusariumwilt encounteredm substrates
amende With
'
. art to randomrecolonization
mature~~~~os~~~c~~:~~o~ontrolagentsafter peakheat-
substratesdo not germinatein responseto nutrients
re,
,
leasedin the form of seedor root exudates.The high mlcrobial activity and biomasscaused by the " generaI SOt
'I
microflora" in such substrate~pre~entsgermination of
~g~O~~ldco~post more consistentlysuppressesRhizoc-
sporesof thesepathogensand mfection of the host,(Chen
48
"
,
,
X Congreso
Naciona/AgronomicofIll Congreso
deFitopat%gia 1996
l
H.A. .J. Hoitink, A. G. Stone and D. Y. Han
et al., 1988a;Mandelbaumand Hadar 1990). Propagules
of thesepathogensremain dormant and are typically not
killed if introducedin compost-amended
soil (Chenet al.,
1988a;MandelbaumandHadar, 1990).An enzymeassay,
that determines
microbial
.
. . activity basedon the
. rate ofhy-
drolysls
offluorescem
dlacetate
(FDA),
predictssuppres.
..
..
slvenessofpottmg mixesto Pythlumdiseases(Boehmand.
Hoitink 1992;Chenet al., 1988a;MandelbaumandHadar
1990. Y
d S. .th
1994) S. .1 . fi
, ouan
Ivasl
amparam,
. .Iml&: arm" ormah
b
d
I
dfi
.1
h
t Ion
. as een eve ope or SOls on "organic
larms were
Ib
d
.
I
I
t
(W
kn
h
t
I
1993)
. orne Iseases
SOl
are essprevaen
or e ea. ,.
Th I th f t . th t th
.
ffi t I t I
e eng 0 Ime a e suppressivee ec as s a so
b
d
t
.
d
' th FDA t . .ty (B hm d H ' t ' k
may e e ermme WI
ac IVI
oe an 01m ,
1992) Th . . kn
th ".
'ty " f th
,
IS IS own as e carrymg capaci 0 e
b tr t
I t ' t b. I ' I
tr I
su s a e re a Ive 0 10oglca con o.
The mechanismof biological control for Rhizoctonia
solani in compost-amended
substratesis differentfrom that
of Pythiumand Phytophthoraspp,becauseonly a narrow
groupof microorganisms
is capableof eradicatingR.solani.
This type of suppressionis referred to as "specific suppression"(Hoitink et aI" 1991), Trichodermaspp,including T hamatumand T harzianum,are the predominant
hyperparasites
recoveredfrom compostspreparedoflignoII I '
t (K t
t I 1983. N I
t I 1983)
ce u OSIC
was es u er ea.,
, e sonea.,
H
't
.
.
bl f I ., .
I
yperparasl
t
th
es
are
microorganisms
It .'
I
capa
d
'
e 0
th
co
Th
ornzmg
fu
'
p anpa ogensresu mg m YSlSor ea.
ese ngl
.
b t ' I tr . ' th b. I . I
. t eract WI.th various
m
ac ena s aIDSm e 10oglca contr I f Rh ' t . d
.
ff (K k t I 1987) It .
0 0
lZOComa ampmg-o
wo e a"
. IS
th
d . th
f
' t
t
th
t
P
. 'II .
0 meres a emCI lum spp. are e pre omman yperparasitesrecoveredfrom sclerotiaof Sclerotiumrolfsii
.
.
m
and low
I composted
t t grape
t (Hpomace
d
'daGhighdsugar
k ' 1991
) '7'.celluh
osecon en was e a ar an oro ec I,
, 1 rlC 0t
d fr
th'
t d
J
uerma
spp.wereno recovere om IScompos an were
..
..
not effective when mtroduced, The composItionof the
.
feed stock,as expected,appearsto havean Impacton the
microflora in compostsactive in biological control.
matter due to high glucose concentrationsin such waste
(de la Cruz et al., 1993). The sameprocessesmay occurin
antibiotic production, which also plays an importantrole
in biocontrol.
ffr
.
I
h
.
n maturecompost,were concentrations
0 eenutrlI (Ch
I 1988 ) I
. fR
I .
entsare owen
et a .
a sc erotla0 . so am are
:'..
.
kIlled by the hyperparasite,andb~ologlcalcontrol prevaIls
(Nelsonet al., 1983). The foregomgrevealsthat composts
b d
I
b.l . d
h
..
must e a equatey sta I Ize to reac that decomposItion
..
level wherebiological control ISfeasible. In practice,this
.
occurs m composts (tree barks, yard wastes, etc.) that have
. ,
"
,
been(I) stabIlizedfar enoughto avoid phytotoxIcity and
.
".
(2) colornzedby the approprIatespecific mlcroflora.
Pr . I ' d I '
th d fi
h. ,.
actlca gul e IDes at e met IScntlcaI stage0fd ecomf . I .
, .,
pOSItion m terms 0 blo oglcal control are not yet
available.Industry presentlycontrolsdecompositionlevel
by maintaining constantconditions during the entire processand adheringto a given time schedule,Composted
pine bark produced by such a processhas beenutilized
with great successin floriculture indicating that this
approachto quality control is quite acceptable(Hoitink et
al,,1991).
,.
..
,
ExcessivelystabIlizedorganicmatter,the oppositeend
f h d
..
0 t e ecompOSltion scale, does not support adequate
, ,
activity
of
.
blocontrol
.
agents.
As
a result,
suppression
.
IS
.
.
.
lackmg and soIlborne diseasesare severe,as in highly
.
,.
,
mmerahzedsoIlswherehumic substances
arethepredomi,
nant forms of organicmatter(Workneh et aI" 1993). The
I
h f.
h
'I '
edngt 0 I tImle tf abt .SOI -mco l rpo~a~ed
h composts support
a equate eve s 0 locontro activity asnot Yet beendetermined. Presumably,it varieswith soil temperature,soil
, .
.
characterIstIcsand the type of orgarncmatterfrom which
th
d
d'
.
e compostwasPrepare. Loa mg rates and farmm g Prac.
tIcesof coursealso playa role.
We have studied the "carrying capacity" of soil organicmatterin potting mixespreparedwith sphagnumpeat
5. BIOLOGICAL ENERGY AVAILABILITY
to bring a partial solution to this problem (Boehm and
VERSUS SUPPRESSIVENESS
Thedecompositionlevel of organicmatterin compostamendedsubstrates
hasa major impacton diseasesuppression. For example,R. solani is highly competitive as a
saprophyte(Garrett, 1962), It can utilize cellulose and
colonize fresh wastesbut not low cellulosematurecompost (Chung et aI" 1988). Trichoderma, an effective
biocontrol agentof R.solani,is capableof colonizingfresh
aswell asmaturecompostbut it growsbetterin freshcompost (Chung et al., 1988;Nelson et al., 1983). In fresh,
undecomposed
organicmatter,biological control doesnot
occur becauseboth the pathogenandthe biocontrol agent
grow as saprophytes.Therefore,R. solani (the pathogen)
remainscapableof causingdiseasehere. Prfsumably,synthesis of lytic enzymesinvolved in hyperparasitismof
pathogensby Trichodermais repressedin fresh organic
Hoitink 1992;Boehm et al., 1993). Sphagnumpeattypically competeswith compostasa sourceof organicmatter
in horticulture, Both the microflora andthe organicmatter
in peat itself can affect suppressionof soilbornediseases.
The literatureon that effect is reviewedbriefly here.
Dark, more decomposedsphagnumpeat, harvested
from a four foot or greaterdepthin mostpeatbogs,is low
in microbial activity andconsistentlyconduciveto Pythium
and Phytophthoraroot rots (Hoitink et al., 1991;Boehm
and Hoitink, 1992). On the otherhand,light, lessdecomposedsourcesof sphagnumpeat,harvestedfrom nearthe
surfaceof peatbogs,havea highermicrobialactivity (FDA
activity) andsuppressroot rot. Unfortunately,the suppressive effect of light peat to Pythium root rots is of short
duration. (Boehm and Hoitink, 1992; Tahvonen, 1982;
Wolffltechel 1988). Light peatsareusedmost effectively
X Congreso
NacionalAgronomico/ III Congreso
deFitopatologia1996
49
~
-
-~
Suppressionalp/ant diseasesby...
for short prod~ctioncyc..es(6-10 week cr~ps),suchas in
plug andflat mIxesu~edm the ornamentalsmdu.s~. Compostshavelongerl~tmg effec~ (B~ehmandHoItmk, 1992;
Boehmet aI, 1993,You and Sivasithamparam,1994).
Unfortunately, efficacy varies with the compost,batches
of steepagesproduced,cropsand the diseaseunder question. Sackenheim(1993), utilizing plate counting procedures,hasreportedthat aerobicmicroorganismspredomi-
As mentionedabove,therateof hydrolysisof FDA predicts suppressivenessof peat mixes and of compostamended substrates to Pythium root rot (Boehm and
Hoitink, 1992). As FDA activity in suppressivesubstrates
declinesto < 3.2 =B5g FDA hydrolyzed min-l g-1 dry
weight mix, the populationof Pythium ultimumincreases,
infection takes place and root rot develops. During this
collapsein suppressiveness,
the compositionof bacterial
speciesalso changes(Boehmet al., 1993). A microflora
typical of suppressivesoils, which includesPseudomonas
spp. and other rod-shapedGram negativebacteriaas the
predominantrhizospherecolonizers,is replacedby pleomorphic Gram-positivebacteria (e.g., Arthrobacter) and
putativeoligotrophs(Wu et al., 1993). The microflora of
the conducive substrateresemblesthat of highly mineralized nichesin soil (Kanazawaand Filip, 1986).
.
.
..
..
. Non-.destructlveanalysIsof soil organicmatter,utIlIZmg FounerTransformInfra Redspectroscopy(FT-IR) and
Cross Polariza~ion Magic Angle Spinning -13Carbon
NuclearMagnetIcReson~c~Spectro.scopy
(CPMAS- 13C
NMR), allows charactenzation
of
biodegradable
compof .1
. fr . ( b
nents0 SOlorganic actions In ar et al., 1989;Ch~n~d
Inbar, 1993). CPMAS - 13CNMR allows quantitative
analysisof concentrationsof readily.biodegradablesubstancessuchas "carbohydrates"(hemicellulose,cellulose,
etc.) versuslignins and humic substancesin soil organic
matter [reviewed in Chenand Inbar, 1993]. In a preliminary report, Wu et al. (1993) reportedthat the "carbohydrates"declineassuppressiveness
is lost. During the same
time period,bacterialgeneracapableof causingbiological
control are replacedby thosethat cannotprovide control.
Biocontrol agentsinoculated into the more decomposed
substrateare not able to induce sustainedbiological control of Pythiumroot rot. The samephenomenonhasbeen
observedfor Phytophthoraroot rot in the field (You and
Sivasithamparam,1994). Therefore,biocontrol of these
diseasesis determinedby the "carrying capacity" of the
substratewhich.regulatesspeciescompositionandactivity
and,in turn, the potentialfor sustenance
of biological control.
nate in steepages.The microflora includesstrainsof bacteria and isolates of fungi already known as biocontrol
agents. He developeda numberof enrichmentstrategies,
that include nutrients as well as microorganisms,to improve efficacy of the steepages.
OUTLOOK
. ..
'.
. Suc.cess
m bl~loglcal contr~lof dlse~esWithcomp~sts
IS pos~I~le~nly If all factors Involved m the production
and utilization of compostsare defined and kept consistent. Most compostsare variable in quality. Therefore,
compostedpine bark remainsthe principal compost used
for th.eprepar:ationof potting mixes or soils naturally suppresslveto soilborneplantpathogens.Compostedmanures,
yard and food wastesar~ steadily gai~ing in popularity,
and offer the samepotential(Gorodeckland Hadar, 1990;
Grebusetal., 1994;Inbar et al., 1993;Marugget al., 1993;
SchUleret al., 1993).
6. COMPOST FOR CONTROL OF FOLIAR
DISEASES
.
..
Durmg the past decade,a senesof projectshavebeen
Controlled inoculation of compostswith biocontrol
agentsis a procedurethat must be developedon a commercial scaleto induceconsistentlevelsof suppressionto
pathogenssuch asR. solani (Hoitink et al., 1991;Phaeet
publishedon~hecontrolofplantdiseasesofaboveground
plant parts With water extracts,als.oknown as steepages,
preparedfrom composts (Weltzhlen, 1992; Yoh.alemet
al., 1994). Ste~pagesofte~ are preparedby soakingmature compostsm w~ter (still culture; 1:1, w/w) for 7-10
days. The steepageISfiltered and then sprayedon plants.
al., 1990; Grebuset al., 1993). Recently,tree bark was
proposedasa food basefor the cultureofbiocontrol agents
andasa carrierof suchagentsfor usein agriculturalapplications(Steinmetzand Schl>nbeck,1994).However,this
new field of biotechnology,is still in its infancy. Major
researchand developmentefforts will needto be directed
50
Control induced by compoststeepageshas also been
attributed to systemicacquiredresistance(SAR) induced
in plants by microbespresentin the extracts(Weltzhien,
1992). The recentwork by Sackenheim(1993) on grape,
however,doesnot supportthis assumption.A factor that
hasnot beenevaluatedbut could playa role in efficacy of
steepagesis the condition of soil organic matter and the
associatedmicroflora in the soil in which treatedplantsare
produced. Soils naturally suppressiveto soilborneplant
pathogens(e.g., compost-amendedsoils) harbor active
populations of biocontrol agents(Boehm et al., 1993).
Severalof theserhizobacteriaand fungi can induce protectionto foliar pathogensin the leavesof plants(Ma h ti
et al., 1994; Wei et al., 1991). Zhang et al., (19~)or:~
ported that pathogenesis- related proteins were activated
. comin roots and shootsof cucumberPlantsProduced m
post. Further work may revealthat compostsaffect resistanceof the roots and foliage to diseases.Presentl
trol of foliar diseaseswith compostsor steepages
iS~i;~y
variable.
7. DISEASE SUPPRESSION - FUTURE
X CongresoNacional Agronomico / III Congresode Fitopatologia 1996
~
H.A..J: Hoitink, A.G. Stoneand D.Y. Han
toward this approach for disease control. Recycling through
composting is being chosen as the preferred strategy for
.
waste
treatment.
ThIs
also
.
applIes
to farm
manures.
Fqr
this reason, composts are becoming available in greater
quantities.
Peat, on the other hand, is a limited resource
that cannot be recycled. Future opportunities
I
ra an
d
con
tr II d . d
0 e -In uce
d
.
f
for both natu-
.lb
I t
suppressIon 0 SOl orne p an
Farrell, J. B. 1993. Fecalpathogencontrol during composting,p. 282300. In: Science and Engineering of Composting: Design,
Environmental,
Microbiological
A. J. Hoitink and H. M. Keener,
and Utilization
eds. Renaissance
Aspects.
H.
Publications,
Worthington, OH. 728 p. Garrett, S. D. 1955. A century of
root-dise~e investigation. Ann. Appl. Bioi. 42:211-219.
Garrett.,S. D. 1962. Decompositionof cellulosein soil by Rhizoctonia
solani Kuhn. Trans. Br. Mycol. Soc. 45:114-120.
pathogens appear bright.
Grebus, M. E., K. A. Feldman, C. A. Musselman, and H. A. J. Hoitink.
8. ACKNOWLEDGEMENT
1993. Production of biocontrol agent-fortified compostamendedpotting mixes for predictable diseasesuppression.
Phytopathology83:1406 (Abstr.).
Salaries and research support provided by State and
federal funds appropriated to the Ohio Agricultural
Research and Development Center The Ohio State Univer.
db G
t
US2 I 96-22 from BARD the United
Slty, an
y ran no.
,
States-Israel Binational Research and Development Fund.
Grebus,M. E., M. E. Watson,and H. A. J. Hoitink. 1994. Biological,
ch~mi.caland physic~1propertieso~compostedy~d trimmings
asIndicatorsofmatunty andplant diseasesuppression.Compost
Sci. Util. 1:57-71.
9. REFERENCES
Gorodecki,B. and Y. Hadar. 1990. Suppressionof Rhizoctoniasolani
and Sclerotium rolfsii in container media containing composted
Boehm, M. J. and H. A. J. Hoitink. 1992. Sustenanceof microbial
activity and severity of Pythium root rot of poinsettia.
Phytopathology82:259-264.
Boehm, M. J., L. V. Madden, and H. A. J. Hoitink. 1993. Effect of
organicmatterdecompositionlevel on bacterialspeciesdiversity
and composition in relationship to Pythium damping-off
severity. A lied Environ. Microbiol. 59:4171-4179.
pp
Bollen, G. J. 1993. Factorsinvolved in inactivation of plant pathogens
separat.edcattle manure and composted grape marc. Crop
ProtectIon9:271-274.
.
..
.
Hadar, Y. and B. Gorodeckl. 1991. Suppressionof germmation of
sclerotiaof Sclerotiumrolfsii in compost. Soil. Bioi. Biochem.
23:303-306.
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