Abstract:
Cry
genes encoding Cry proteins toxic to Lepidoptera,
Coleoptera and Diptera species
were studied in thirty seven
B. thuringiensis
strains isolated from twelve naturally infested
Heliothis armigera
larvae. To further confirm the isolates, two group
s of species-indicative
biochemical tests were applied while discriminative
biochemical tests being employed to
figure out the repetitive strains. A PCR experiment
was performed using five sets of
universal primers for
cry1, cry2, cry3, cry4, cry7/8
genes. All strains reacted appropriately,
for
B. thuringiensis
, to the biochemical tests and while the reactions
to the discriminative
tests being varied. Based upon the results of the d
iscriminative tests,
twenty four non-
repetitive strains were selected and employed in th
e PCR assay. Each of the selected
strains presented one
cry
gene, at least;
cry1
being the most frequently detected one
(91.7%
), followed by
cry2
(87.6%
),
cry3
(50%
) and
cry4
(42%
) but no isolate harbored a
coleopteran-active
cry7/8
gene. All the strains presented combinations of tw
o or more
cry
genes: 20%
presenting
cry1+cry2
, 12.5%
cry1+cry3
, 4%
cry2+cry4
, 20%
cry1+cry2+cry3
,
20%
cry1
+
cry2+cry4
, 4%
cry1+cry3+cry4
and 12.5%
carrying all the four
cry
genes
studied and only one strain bearing a single
cry
gene. The
cry1-cry2
combination was
common in many strains (72.5%
). Genetic characterization of this collection prov
ides an
opportunity for selection of strains with improved
and multiple insecticidal toxicity.
Keywords
:
Bacillus thuringiensis
, Biochemical characters
, Cry
, PCR.
