© Benaki Phytopathological Institute
Hellenic Plant Protection Journal - Special Issue
64
For this purpose, a talc preparation of Κ165
was either incorporated into the soil (in a
proportion of 1%, 5%, 10% and 20%) that
was used to grow melon plants, or was used
as a seed coating. At the stage of the 2
nd
leaf
the plants were transplanted to soil infest-
ed with 10
3
Fusarium oxysporum
chlamy-
dospores per gram of soil. It was observed
that the 10% treatment alone resulted in
a statistically significant reduction in dis-
ease severity. It is noteworthy that applica-
tion of the biocontrol agent at 20% result-
ed in partial reduction in disease severity
that was not statistically different from the
effective treatment of 10% but at the same
time the severity of the disease in this group
was not statistically different to that in the
non-treated controls. It is tempting to spec-
ulate that this difference may be attributa-
ble to the phenomenon of quorum sensing
as the size of the rhizosphere population of
the 20% treatment group was 2-4 fold high-
er than that of the 10% treatment. On the
other hand, the size of the K165 rhizosphere
population of the other ineffective treat-
ments (1%, 5% and seed coating) was sub-
stantially lower than that seen with the ef-
fective treatment of 10%.
Isolation of new biocontrol agents against crown and root rot disease of
tomato caused by
Fusarium oxysporum
f. sp.
radicis – lycopersici
N.N. K
AMOU
1
, L. L
OTOS
, G. M
ENEXES
2
and L.A. L
AGOPODI
1
1
Plant Pathology Laboratory, School of Agriculture, Aristotle University of
Thessaloniki, GR-541 24 Thessaloniki, Greece.
2
Agronomy Laboratory, School of
Agriculture, Aristotle University of Thessaloniki, GR-541 24 Thessaloniki, Greece
The need to limit the irrational use of chem-
ical fungicides in plant protection, has led to
a tendency to use biological control. In the
present research, 383 rhizobacteria, isolat-
ed from cultivated plants from different re-
gions of Greece, were studied.
Fusarium ox-
usporum
f.sp.
radicis – lycopersici
(Forl), which
causes crown and root rot disease in tomato
was chosen as a target pathogen. The inhib-
itory activity of the bacteria on the fungus,
was tested
in vitro
and
in planta
. For the
in
vitro
experiments, a lysis bioassay was per-
formed and the presence of a potential inhi-
bition zone of fungal growth was examined,
in multiple and dual cultures of the fungus
and the bacteria in Petri dishes. The most ef-
fective bacteria in the two previous bioas-
says were identified by sequencing the 16S
rRNA
gene, or the intergenic spacer region
between 16S and 23S
rRNA
. In the
in planta
tests that followed in a gnotobiotic system in
pots, and in one indicative field experiment,
the disease caused by artificial inoculation
of tomato plants with the fungus was signif-
icantly reduced by the selected rhizobacte-
ria. Moreover, the ability of these rhizobac-
teria to promote the growth of tomato was
studied in pot experiments. Finally, the
presence of antifugal metabolites in the liq-
uid culture supernatants of the biocontrol
agents and their organic extracts was inves-
tigated. The effect of the metabolites on the
growth of the fungus was studied by filter
paper, TLC, and microtitre bioassays. The re-
sults demonstrated that the strains
Bacillus
cereus
S76 and S79,
Serratia rubidaea
S55 and
S49,
Serratia marcescens
PiHa5II, S52 and S47
and
Pseudomonas chlororaphis
ΤοZa7 are ef-
fective biocontrol agents that successfully
inhibit the growth of Forl, and the disease
intensity caused by this fungus in tomato. In
addition, the strains
S. marcescens
S47,
B. ce-
reus
S76 and S79 and
P. chlororaphis
ToZa7,
showed a statistically significant promotion
of tomato plant growth in pots and in the
field.
Biological control of the toxigenic fungus
Aspergillus flavus
and aflatoxins
produced in shelled pistachio nuts cv. “Eginis”
