Bt Research 2012, Vol.3, No.3, 11
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migration of bacteria to places where seeds are
germinating and roots growing (Hinton and Bacon,
1995).
One isolate of
Bacillus
and another of
Pseudomonas
applied to seeds of Norway spruce
(
Picea abies
)
have been observed to move aploplastically,
in the intercellular spaces, being found on branches,
leaves and flowers (Shishido and Chanway, 1999),
colonizing the plants endophytically. Their penetration
and transport mechanisms, however, are not known.
The ecology of
B. thuringiensis
is also little understood.
To use it endophytically in the control of insect
pests it is important to understand the way that
B.
thuringiensis
colonizes cabbage seedlings, so that it
may be used in controlling insect pests that live and
feed within plant tissues.
The Laboratory of Entomopathogenic Bacteria at
Embrapa Genetic Resources and Biotechnology has,
since 2003 (Monnerat et al., 2003), been studying a
new way of controlling
Plutella xylostella
using
B.
thuringiensis
in its endophytic form, with the aim of
protecting cabbage crops and other brassicas from this
important cryptic pest.
The objective of this work was to evaluate the
colonization of Brazilian
B. thuringiensis
strains toxic
to
P. xylostella
of cabbage seedlings cultivated
in vitro
,
by means of scanning electron microscopy. This study
opens up prospects for systemic use of this bacterium
in the control of agricultural pests from the Lepidoptera
order. In addition, the study evaluated the possible
positive effect caused by various strains of
B.
thuringiensis
on seed germination and on seedling
development, in cabbages cultivated
in vitro
.
1
Results
1.1
Development of cabbage seedlings inoculated
by Brazilian
B. thuringiensis
strains
Results of the experiment to evaluation cabbage seed
germination and seedling development three days after
planting showed that there were no statistically
significant differences when Brazilian
B. thuringiensis
strains were compared to the two negative controls
(
Table 1). This indicated that bacterial strains did not
inhibit or stimulate germination (Kruskal-Wallis:
H
5
=3.4; P=0.639) or seedling development (Kruskal-
Wallis: H
5
=11.679; P=0.039) soon after germination.
Table 1 The effect of
B. thuringiensis
strains in development of
cabbage seedlings after germination (average±standard deviation)
Treatment
Length of seedling
(
cm)
Percentual of
germination
Control
3.111
±1.079 a
100.00
±0.000a
Embrapa medium 3.694±1.742a
100.00
±0.000a
S1905
4.688
±2.496a
94.44
±9.624a
S2122
4.559
±1.648a
100.00
±0.000a
S2124
3.667
±1.590a
94.44
±9.624a
S1450–Btk
3.500
±1.620a
94.44
±9.624a
Note: Measurements followed by the same letter, in the column,
do not differ among themselves
As regards development of seedlings after 30 days,
stimulatory and inhibitory effects could be observed
and varied depending on the bacterial strains and
controls used (Table 2).
Thirty days after germination, growth of the aerial part
was positively induced by
B. thuringiensis
strain
S1905 (±27%) when compared to strain S1450 Btk,
but when compared to the controls it did not present a
Table 2 Effect of
B. thuringiensis
strains on development of cabbage seedlings
Treatment
Length of aerial part
(
cm)
Length of roots
(
cm)
Weight of fresh material
(
g)
Weight of dry material
(
g)
Number of leaves
(
unit)
Control
8.27
±1.041ab
9.88
±1.417a
0.500
±0.0636a
0.0277
±0.003a
2.9
±0.316a
Embrapa medium 8.08±1.948ab
7.52
±2.004a
0.459
±0.0705a
0.0239
±0.0041ab
3.0
±0.000a
S1905
8.96
±1.526a
8.70
±1.274a
0.285
±0.0671b
0.0193
±0.0058b
3.0
±0.470a
S2122
7.40
±1.518ab
9.07
±3.375a
0.310
±0.112 b
0.0210
±0.0055b
3.1
±0.568a
S2124
8.75
±0.995ab
9.67
±5.147a
0.319
±0.0486b
0.0205
±0.0042b
2.7
±0.483a
S1450–Btk
7.05
±0.765b
8.89
±1.025a
0.305
±0.0795b
0.0195
±0.0060b
3.0
±0.000a
Note: Measurements followed by the same letter, in the column, do not differ among themselves
