Voi 611997): S4I-345.

Effect of soil-spraying time on root-colonization
ability of antagonistic Streptomyces

Hanna Kortemaa
Department ofPlant Biology, Plant Pathology, PO Box 28, FIN-00014 University ofHelsinki, Finland.

Current address: KTTK, Seed Testing Department, PO Box 111. FIN-32201 Loimaa, Finland,
e-mail: hanna.kortemaa@mmm.fi

Kielo Haahtela
Department of Biosciences, Division ofGeneral Microbiology, PO Box 56, FIN-00014 University of

Helsinki, Finland

Aino Smolander
Vantaa Research Centre. Finnish Forest Research Institute, PO Box 18, FIN-01301 Vantaa, Finland

The root-colonization ability ofStreptomyces griseoviridis Anderson et al. was tested on turnip rape
(Brassica rapa subsp. oleifera DC.) and carrot (Daucus carota L.) by the sand-tube method. Non-
sterile sand was sprayed with a microbial suspension immediately or 7 days after the seed had been
sown. Results expressed as population frequencies and densities indicated that S. griseoviridis effec-
tively colonizes the rhizosphere when the microbe is applied immediately after sowing but less effec-
tively when it is applied 7 days later. Detection values of S. griseoviridis were higher for turnip rape
than for carrot. In sterile sand, S. griseoviridis invaribly colonized the rhizosphere of turnip rape after
each of the two applications. These findings indicate that S. griseoviridis can compete with indige-
nous soil microbes in the rhizosphere if it is sufficiently abundant in the soil before the seed emerges.
If applied later, however, it competes rather poorly. In root-free nonsterile sand, S. griseoviridis dis-
persed and survived well. r

Key words: actinomycetes, biological control, Brassica rapa ssp. oleifera, Daucus carota, plant growth-
promoting rhizobacteria (PGPR), rhizosphere

ntroduction
S. griseoviridis, a biocontrol agent used against
some seed-borneand soil-borne plant pathogens
(Tahvonen 1988), produces the auxin indole-3-

acetic acid (IAA). The concentration of lAA pro-
duced on solid media by S. griseoviridis is of
the same magnitude as that reported to have a
growth-promoting effect (Tuomi et al. 1994).
Mycostop (Kemira Oy, Finland) is a biofungi-
cide produced by fermentation of the spores and

© Agricultural and Food Science in Finland
Manuscript received March 1997

341

AGRICULTURAL AND FOOD SCIENCE IN FINLAND

https://www.c-info.fi/en/info/?token=Q6YysS3UEt5I3smc.BenP0HVQRwJEEzm367g6Cw.R_XS3bay7DNwMGAvRjMKdd8k6khg1vMzPIyxFO-l8D8Vjb6Mc1tE_krIGej-a4Arke8hx90AwZoCY4fVzGJPsUu4pkmlDWBGp1paZw7NM5KyvTfmVXX-E2u5ZIhCAkceqd7fKeiU1CV3Qc5vrgvq9kR8rsxdaQdH9d8G8qAqkkaabwnXUBP72pq4-23-PHLv9tso4Q17CqbxSbginGZ9b4ea8-4TIB36goO9kUg7AzfdlR4JWDaswFCQIFhzerocnPGQqf3jBqgkCdYQAi_YsOp2gVNKnrrgqKqFMhhHSYbuFONonw


Kortemaa, H. et al. Effect ofsoil-spraying time on Streptomyces griseoviridis

mycelium of a S. griseoviridis strain isolated
from peat by Tahvonen (1982).

Several isolates ofStreptomyces spp., includ-
ing the S. griseoviridis isolated from peat, pro-
duce polyene antibiotics. In contrast to nonsup-
pressive isolates most of the suppressive isolates
produce a candicidin-type antibiotic (Raatikai-
nen et al. 1993). Scanning electron microscopy
studies show that S. griseoviridis is a hyperpar-
asite ofvarious plant pathogenic fungi (Tapio and
Pohto-Lahdenperä 1991). Besides antibiosis and
parasitism, competition is often mentioned as a
mechanism ofbiocontrol. According to Sivan and
Chet (1989), the inhibition of germination of
chlamydospores might be due to competition
between Trichoderma harzianum Rifai and
Fusarium oxysporum Schlecht.: Fr. Rothrock and
Gottlieb (1984), on the other hand, showed that
the antagonism of S. hygroscopicus var. gelda-
nus was due to the antibiotic production, not to
competition for nutrients.

Microbes that colonize roots are ideal for use
as biocontrol agents against soil-borne diseases
(Weller 1988). Because soil spraying, like seed
dressing is, an application method that has re-
sulted in good biocontrol, our objective was to
study how roots of turnip rape and carrot are
colonized after soil-spraying treatment and to
test whether application time has any effect on
root colonization. We tested the root-coloniza-
tion ability in both nonsterile and sterile sand to
establish the effect of microbial competition in
therhizosphere on the colonization potential. As
well as the growth ofS. griseoviridis in the rhizo-
sphere, we examined the dispersal of this antag-
onist in root-free sand.

Material and methods

Root colonization in nonsterile sand
The dispersal of S. griseoviridis in the rhizo-
sphere was tested by the sand-tube method as
described by Ahmad and Baker (1987) and Kor-

temaa et al. (1994). Seeds of turnip rape, Brassi-
ca rapa subsp. oleifera cv. Kulta, and carrot,
Daucus carota cv. Nantes Fancy, were surface-
sterilized with ethanol and sodium hypochlorite
(NaOCl) as described by Kortemaa et al. (1994).
PVC-plastic tubes 20 cm long and 3.2 cm in di-
ameter were longitudinally sliced and fastened
together with rubber bands. The tubes were
blocked at the bottom with cotton wool and filled
with nonsterile, sieved (0.5-1.2 mm) sand (pH
6.2). The sand, water and water-soluble fertiliz-
er were mixed as described earlier, resulting in
a water potential of - 1 kPa (Kortemaa et al.
1994). One surface-sterilized seed was sown in
each tube, and the tubes were placed vertically,
five per each plastic pot containing the same sand
mixture. A microbial suspension was prepared
of Mycostop biofungicide as a 0.01% suspen-
sion in water. The average colony-forming unit
(cfu) value of S. griseoviridis of the suspension
detected on semi-selective water agar with glyc-
erol (Kortemaa et al. 1994)was 8 x 104 ml 1 ; sml
of this microbial suspension was spread evenly
with a pipette on the sand surface in each tube
immediately after sowing (day 0) or was applied
7 days after sowing. The pots were covered with
plastic bags, and no water was added after sow-
ing. The pots were incubated for 4 weeks in a
growth chamber (16 h light period, light inten-
sity 150 mMols'm 2at 20°C and 8 h dark period
at 18°C).

After 4 weeks, the tubes were opened, and
the roots were cut into 2 cm segments. The sand
adhering to the root segments was considered as
rhizosphere soil. For population-density counts,
the cfu values were determined by a dilution-
plating method on water-agar plates, although
this method did not permit population densities
lower than 102 cfu g ] soil to be detected. Sand-
free root segments and above-ground portions
of seedlings, i.e. stems and leaves, were placed
on water-agar plates to isolate S. griseoviridis.

Root-colonization frequencies were counted
for root segments and the rhizosphere, and the
population density was counted as cfu g' 1 rhizo-
sphere soil. Each experiment comprised 10plants
of turnip rape and carrot and the two application

342

AGRICULTURAL AND FOOD SCIENCE IN FINLAND



Vol. 6 (1997): 341-348.

times for the suspension. Five control plants were
not treated. The experiment was conducted three
times.

Root colonization in sterile sand
For this experiment, turnip rape was grown in
sterile sand in a large glass pot containing four
longitudinally sliced tubes. The sand was steri-
lized for I h and other material for 20 min at
121°C in an autoclave. A water suspension of S.
griseoviridis, which had grown for 7 days on
glucose-yeast-malt agar (GYM) (Kortemaa et al,
1994), was prepared for the spraying treatment
instead of Mycostop suspension. The average
population density of the suspension, which
mainly consisted of spores of 5. griseoviridis,
was 6.5 x 106 cfu ml 1 . For these experiments,
the sterile seed was sown, the sand-tubes were
incubated, and S. griseoviridis was applied and
isolated as described above. The only exception
was that for population density counts the mi-
crobe was isolated in the same manner for one
tube in each pot on water-agar and GYM-agar
plates to ensure that the sand was not contami-
nated with other microbes. Each experiment con-
tained one untreated control pot and three pots
with the two application times of the S. griseo-
viridis suspension. The experiment was conduct-
ed twice.

Dispersal in nonsterile sand
without plants

For this experiment a large plastic box (40 cm x
60 cm) and 32 plastic tubes were filled with the
nonsterile sand-water-fertilizer mixture de-
scribed above. The tubes were placed randomly
in the box in a vertical position. Five millilitres
of 0.01% Mycostop suspension was pipetted
evenly onto the surface of each sand-tube; after
this treatment, the tubes were not watered. The
average population density of the suspension was
3 x I04 cfu ml 1. The box with the sand tubes,

which was covered to avoid loss ofmoisture, was
incubated in a growth chamber under the condi-
tions described above for 4 weeks. Each week
(7, 14, 21 and 28 days after treatment), eight
tubes were randomly taken as a sample for meas-
urements of population frequencies and densi-
ties at different depths of sand. The soil for these
counts was sampled at every 2 cm between 0 and
12 cm from the top of the tube. The population
density was counted by the dilution-plate meth-
od on water-agar plates. The experiment was
conducted twice.

Statistical analysis
Cfu values were logarithmically transformed
before analyses of variance [PROC GLM (SAS
Institute Inc. 1988)].Tukey’s Studentized Range
(HSD) Test was used to compare significantly
different means.

Results
Root colonization in nonsterile and

sterile sand
When Mycostop suspension was sprayed imme-
diately (day 0) after sowing, the root-coloniza-
tion frequencies on the roots and rhizosphere of
turnip rape and carrot were higher than when the
suspension was applied 7 days after sowing (Ta-
ble 1). The frequency values were higher for tur-
nip rape than carrot. The stems and leaves of
turnip rape seedlings were colonized 100% af-
ter 0 and 73% after 7 days of treatment. For car-
rots, the corresponding values were 77% and
54%.

The differences in population density values
between the two applications were significant
(P=0.05) at all root depths in therhizosphere soil
(Table 2). At a distance of0-2 cm from the seed,
the differences were significant between both
treatments and plant species.

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Kortemaa, H. et al. Effect ofsoil-spraying time on Streptomyces griseoviridis

Table 1.Root-colonization frequency ofStreptomyces griseoviridis on root segments and in rhizosphere of
turnip rape (Brassica rapa subsp. oleifera) and carrot (Daucus carota) after two different spraying times of
Mycostop suspension in nonsterile sand.

Root-colonization frequency (%)

Root a Rhizosphereb

day ODepth (cm) day O day 7d day 7

Brassica
0-2 100 (30)' 100(30)

47 (30)
10(27)
18(19)
0(15)

100(30)
100(29)
100(24)
83 (19)
85 (14)

100(30)
2-4 100(29) 47 (30)
4-6 100(24) 10(27)
6-8 83(19) 23(19)
8-10 85 (14) 0(15)

Daucus
0-2 97 (29) 51(28)

4(25)
0(24)
0(11)
0 (8)

97 (29)
83 (29)
82 (25)
64(17)
22(10)

61 (28)
2-4 83 (29) 7(25)
4-6 82 (25) 0(24)
6-8 65 (17) 0(11)
8-1 23(10) o (8)

a S. griseoviridis isolated from root segments.
b S. griseoviridis isolated from root segments and/or from rhizosphere soil.
c Suspension sprayed on day 0 after sowing.
d Suspension sprayed on day 7 after sowing.
• Number of samples studied (n).

The rhizosphere ofturnip rape was effectively
colonized by S. griseoviridis in sterile sand. The
results for the dilution series on GYM agar
showed that the sand remained uncontaminated
during the experiments. The root-colonization
frequencies were 100%. Population densities

were high, and there were no significant differ-
ences between treatments (Table 3). The stems
and leaves of turnip rape seedlings were colo-
nized 66% and 75% after the 0 day and the 7-
day treatments.

Table 2. Population densities (cfu values) of Streptomyces griseoviridis in rhizosphere ofturnip rape (Brassica
rapa subsp. oleifera) and carrot (Daucus carota) after two different spraying times of Mycostop suspen-
sion in nonsterile sand.

Population density (cfu) 102 g 1 of soil
Depth (cm)

0-2 2-4 4-6 6-8Treatment 8-10

Brassica
day 0
day 7

11 000*
3 100b

2 800* 5 300“
1 100h

I OOO1
3 b

350
nd5l0b

Daucus
day 0
day 7

530 < 1
< 1

270*
nd

<1 < 1
nd nd2201

Means within a column followed by the same letter were not significantly different according to Tukey’s
Studentized Range (HSD) Test (P=0.05). nd: not detected

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Vol. 6 (1997): 341-348.

Table 3. Population densities (cfu values) ofStreptomyces griseoviridis in rhizosphere of turnip rape (Brassica
rapa subsp. oleifera) after two spraying times of spore suspension on sterile sand.

Population density (cfu) 102 g 1 of soil
Depth (cm)

Treatment 0-2 2-4 4-6 6-8 8-10

day 0 39 000 23 000 5 600 7 700 920
day 7 79 000 42 000 13 000 4 000 1900

Means were not significantly different according to Tukey’s Studentized Range (HSD) Test (P=0.05).

Dispersal in nonsterile sand
without plants

S. griseoviridis dispersed well in root-free sand
when 5 ml of Mycostop suspension was sprayed
on the surface of the sand. The isolation frequen-
cies of S. griseoviridis had already reached al-
most 100% at a depth of 0-6 cm from the top 7
days after inoculation (Fig. 1), and continued to
accumulate over the next 2 weeks (14 and 21
days after treatment).

The population densities of S. griseoviridis
isolated from different depths in the sand tube
were highest at the top and decreased with depth
(Fig. 2). The population of S. griseoviridis was
stable during the experiment; differences in pop-

ulation densities between sampling days were not
significant (P=0.05) for any depth category.

Discussion
Root colonization was more effective when S.
griseoviridis was applied to nonsterile sand im-
mediately after sowing than when it was applied
7 days later, probably because during those days
the rhizosphere was colonized by other soil mi-
crobes with which S. griseoviridis was unable
to compete. The results of sterile-sand experi-
ments, in which the rhizosphere was 100% col-

Fig. I. Accumulation of isolation
frequencies of Slreptomyces gri-
seoviridis at different soil depths
during 28 days after spraying of
Mycostop suspension on root-free
sand.

345



Kortemaa, H. et al. Effect ofsoil-spraying time on Streptomyces griseoviridis

onized by S. griseoviridis after both treatment
times, support this contention.The higher popu-
lation densities in sterile than in nonsterile sand
are probably due to the higher inoculation den-
sities and lack of competition with other mi-
crobes in sterile sand. The number of micro-or-
ganisms in nonsterile sand was probably rather
low, and the absence of many of the microbes,
both plant-growth-promoting and deleterious
strains, to be found in soil with abundant organ-
ic material most likely affected competition.
Scher et al. (1984) noted that microbial compe-
tition negatively affects the root-colonization
capacity of fluorescent pseudomonads in non-
sterile soil.

Isolation frequencies and population densi-
ties were greater for turnip rape than for carrot
because the root exudates of turnip rape were
probably more abundant or more available than
those of carrot. The same results were obtained
in our previous study (Kortemaa at el. 1994) us-

ing the plate test. Sterile plants of turnip rape
and carrot inoculated with S. griseoviridis were
grown on water-agar plates. The difference in
root colonization between the two plant species
was clear. Without the effect of other microbes,
the difference between plant species was sug-
gested to be of plant origin, i.e. due to root exu-
dates or morphological differences.

In both plant species the upper part of the
root was more frequently colonized by S. griseo-
viridis than the lower parts. The population
densities in the rhizosphere of turnip rape were
higher than in the root-free sand experiment but
population densities were lowest in the carrot
rhizosphere. The results are similar to those of
our previous studies, which were done using oth-
er application methods (Kortemaa et al. 1994,
1997). All these differences were probably due
to root exudates (Curl and Truelove 1986)

The soil-spraying treatment method used here
resulted in better dispersal in sand than did seed

Fig. 2. Population densities (cfu values) of Streplomyces griseoviridis at different soil depths during 28 days after spraying
of Mycostop suspension on root-free sand. Differences in population densities between sampling days were not significant
(P=0.05) for any depth category.

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Vol. 6 (1997): 341-348.

treatment (Kortemaa et al. 1994). Root-coloni-
zation was best when the S. griseoviridis sus-
pension was mixed into the sand before sowing
(Kortemaa et al. 1997). After seed treatment, the
antagonist must actively colonize the rhizosphere
with the aid of the root and seed exudates. After
the soil-spraying treatment the antagonist dis-
persed well as shown by the experiment without
plants, the antagonist being available all around
the root. Seven days after seed sowing, therhizo-
sphere was mainly colonized by other soil mi-
crobes and S. griseoviridis was not able to colo-
nize the rhizosphere effectively.

Our results suggest that S. griseoviridis can
compete with indigenous soil microbes in the
rhizosphere if it is well established in the sand
before the seed emerges. If applied to the rhizo-
sphere later, however, it competes rather poorly
with other microbes. According to Lacey (1973),
Streptomyces spp. colonize new substrates more
slowly than do other bacteria and fungi. Our find-
ings suggest that competition is probably not the
main mode of action of antagonistic S. griseo-
viridis.

S. griseoviridis was isolated in great num-
bers in root-free sand with very little organic
material. The antagonist survived well in root-
free sand after the suspension had been mixed
into the sand (Kortemaa et al. 1997). Hatzinger
and Alexander (1994) showed that the bacteria
which survived well in nonsterile soil were
present in the highest population densities in the
rhizosphere. Bahme and Schroth (1987) noted
that the bacteria which survived in nonrhizo-
sphere soil have good potential as biocontrol

agents because the bacteria can await the emerg-
ing seed in the soil. According to Wellington et
al. (1990), populations of S. lividans and S. vio-
laceolatus remain constant or decline in natural
soil, and after a short mycelial growth phase,
sporulation occurs and inoculants survive in the
soil as spores.

Mohammadi and Lahdenperä (1994) found
that seed dressing controls Rhizoctonia solani
Kiihn on cauliflower more effectively than does
soil spraying or the mixing of Mycostop suspen-
sion into the growth substrate. On the other hand,
soil-spraying treatment resulted in better cucum-
ber seed emergence and a better gerbera flower
yield than did other methods. According to El-
Abyad et al. (1993) seed-coating treatment with
antagonistic Streptomyces spp. was a more ef-
fective way of controlling various tomato path-
ogens than was soil inoculation. These results
together with those of the present study support
the idea that both timing and application meth-
od must be right if effective biocontrol is to be
achieved with S. griseoviridis.

The dispersal of S. griseoviridis after soil-
spraying treatment was effective in both the
rhizosphere and root-free sand. The root-colo-
nization ability of the antagonist depended on
the application time. S. griseoviridis could not
compete effectively with indigenous soil mi-
crobes, and the rhizosphere was effectively col-
onized only if the sand was treated immediately
after sowing.

Acknowledgements. We thank Tuula Laine and Lahja Pe-
sonen for their technical assistance.

References
Ahmad, J.S, & Baker, R. 1987. Rhizosphere competence

of Trichoderma harzianum. Phytopathology77: 182-
189.

Bahme, J.B. & Schroth, M.N, 1987. Spatial-temporal col-
onization patterns of a rhizobacterium on under-
ground organs of potato. Phytopathology77: 1093-
1100.

Curl, E.A. &Truelove, B. 1986. The rhizosphere. Spring-
*e?-Verlag, Berlin, Germany. 288 p.

El-Abyad, M.S., El-Sayed, M.A., El-Shanshoury, A.R. &

El-Sabbagh, S.M. 1993, Towards the biological con-
trol of fungal and bacterial diseases of tomato using
antagonistic Streptomyces spp. Plant and Soil 149:
185-195.

Hatzinger, P.B. & Alexander, M. 1994. Relationship be-
tween the number of bacteria added to soil or seeds
and their abundance and distribution in the rhizo-
sphere of alfalfa. Plant and Soil 158: 211-222.

347

AGRICULTURAL AND POOD SCIENCE IN FINLAND



Kortemaa, H. et al. Effect ofsoil-spraying time on Streptomyces griseoviridis

Kortemaa, H,, Pennanen, T, Smolander, A. & Haahtela, K.
1997. Distribution of antagonistic Streptomyces
griseoviridis in rhizosphere and non-rhizosphere
sand. Journalof Phytopathology 145: 137-143.

-, Rita, H., Haahtela, K. & Smolander, A. 1994. Root-
colonization ability of antagonistic Streptomyces gri-
seoviridis. Plant and Soil 163: 77-83.

Lacey, J. 1973. Actinomycetes in soils, composts and
fodders. In: Sykes, G. & Skinner, F.A. (eds.). Actino-
mycetales: Characteristics andpractical importance.
Academic Press, London, p. 231-251.

Mohammadi, O. & Lahdenperä, M.L. 1994. Impact of
application method on efficacy of Mycostop biofun-
gicide. In: Ryder, M.H. et al. (eds.). Improving plant
productivity with rhizosphere bacteria. Proceedings
of theThird International Workshop on Plant Growth-
Promoting Rhizobacteria. CSIRO, Australia, p. 279-
281.

Raatikainen, 0., Tuomisto, J., Tahvonen, R. & Rosenqvist,
H. 1993. Polyene production of antagonistic Strepto-
myces species isolated from Sphagnumpeat. Agri-
cultural Science of Finland 2: 551-561.

Rothrock, C.S. & Gottlieb, D. 1984. Role of antibiosis of
Streptomyces hygroscopicusvar. geldanus to Rhizoc-
lonia solani in soil. Canadian Journal of Microbiol-
ogy 30: 1440-1447.

SAS Institute Inc. 1988. SAS/STAT user’s guide. Release
6.03. Cary, USA. 1028 p.

Scher, F.M., Ziegle, J.S. & Kloepper, J.W. 1984. A meth-

od for assessing the root-colonizing capacity ot bac-
teria on maize. Canadian Journal ofMicrobiology 30:
151-157.

Sivan, A. & Chet, I. 1989. The possible role of competi-
tion between Trichoderma harzianum and Fusarium
oxysporum on rhizosphere colonization. Phytopathol-
ogy 79: 198-203.

Tahvonen, R. 1982. The suppressiveness of Finnish light
coloured Sphagnum peat. Journal of the Scientific
Agricultural Society of Finland 54: 345-356.

- 1988. Microbial control of plant diseases with Strep-
tomyces spp. EPPO Bulletin 18: 55-59.

Tapio, E. & Pohto-Lahdenperä, A. 1991. Scanning elec-
tron microscopy of hyphal interaction between Strep-
tomyces griseoviridisand some plant pathogenic fun-
gi, Journal of the Scientific Agricultural Society of
Finland 63: 435-441.

Tuomi, T., Laakso, S. & Rosenqvist, H. 1994. lndole-3-
acetic acid (lAA) production by a biofungicide Strep-
tomyces griseoviridisstrain. Annales Botani Fennici
31: 59-63.

Weller, D.M. 1988. Biological control of soilborne plant
pathogens in the rhizosphere with bacteria. Annual
Review of Phytopalholology26: 379-407,

Wellington, E.M.H., Cresswell, N. & Saunders, V.A. 1990.
Growth and survival ot streptomycete inoculants and
extentof plasmid transfer in sterile and nonsterile soil.
Applied and Environmental Microbiology 56: 1413-
1419.

SELOSTUS
Kasvualustan käsittelyhän vaikutus Streptomyces griseoviridis -antagonistin juurten

asutuskykyyn
Hanna Kortemaa, Kielo Haahtela ja Aino Smolander

Helsingin yliopisto ja Metsäntutkimuslaitos

Mikrobit, jotka asuttavat tehokkaasti juuria, ovat lu-
paavia biotorjuntaeliöitä käytettäväksi maalevintäis-
ten kasvitautien torjuntaan. Antagonistisen Strepto-
myces griseoviridis -sädebakteerin kykyä asuttaa ryp-
sin ja porkkanan juuria testattiin hiekkaputkimenetel-
mällä. Käsittelemätön hiekka kasteltiin mikrobiliuok-
sella joko välittömästi tai seitsemän vuorokauden
kuluttua siemenen kylvöstä. Tulokset osoittivat, että
S. griseoviridis asutti juurivyöhykkeen tehokkaasti,
jos mikrobikäsittely tehtiin välittömästi kylvön jäl-
keen, mutta selvästi heikommin, kun käsittely tehtiin
viikon kuluttua kylvöstä. Mikrobitiheydet olivat ryp-
sin juuressa suuremmat kuin porkkanan juuressa.
Antagonisti eristettiin juuren yläosasta useammin

kuin alemmista osista. Steriilissä hiekassa S. griseo-
viridis asutti rypsin juuret tehokkaasti molempien
käsittelyaikojen jälkeen. Nämä tulokset osoittavat,
että S. griseoviridis pystyy kilpailemaan maassa luon-
taisesti esiintyvien mikrobien kanssa, jos antagonis-
tia on kasvualustassa runsaasti ennen siemenen itä-
mistä. Jos antagonisti lisätään maahan myöhemmin,
se pystyy suhteellisen huonosti kilpailemaan muiden
mikrobien kanssa. Hyvän biotorjuntatuloksen saavut-
taminen käytännön kasvintuotannossa edellyttää oi-
kean käsittelymenetelmän ja -ajan tuntemista. S. gri-
seoviridis levisi ja säilyi elävänä hyvin steriloimat-
tomassa hiekassa, jossa ei kasvanut kasveja.

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AGRICULTURAL AND FOOD SCIENCE IN FINLAND