Different clonal responses to cypress canker disease based on transcription of suberin-related genes and bark carbohydrates' content

In cypress, the main mechanism of resistance to the bark canker caused by the fungal pathogen Seiridium cardinale
involves
the
post-infectional
development
of a well-structured
necrophylactic
periderm
(NP). The impermeability
and

effectiveness
of
NP
against
pathogens
has
been
associated
with
cell
wall
suberization.
In
canker-resistant
and
susceptible

C.
sempervirens
clones, the
transcript
accumulation of four
genes
involved
in suberin
biosynthesis
(Acyl-CoA
thioesterase,

stearoyl-ACP-desaturase,
Caffeoyl-CoA-3-O-methyltransferase
1 and Peroxidase
21) was
studied
in inoculated and wounded

bark
tissues through
qPCR assay
during
a 3 month
trial.
Quantification of non-structural
carbohydrates
in the
same targeted

tissues
was
also performed
by
HPLC.
In the
canker-resistant
clone, transcript
accumulation of all four
examined
genes

significantly
increased
after
both
inoculation
or
wounding
more
than
in the
susceptible
clone, and
the
maximum
difference

between
the
two
clones was
observed
after
30 days.
The type of clone significantly
affected the
transcript
accumulation of all

the
four
examined
genes
(main effects ANOVA).
The total
soluble sugars
content detected
in the
bark
tissues was
constitutively
similar in both
clones, and only
slight differences
in the
carbon balance were
detected
between
the
two
clones 90 days

after
inoculation or wounding.
Histological
observations
of bark
sections stained
with
Sudan red
90 days
after
inoculation,

showed
that
in
the
canker-resistant
clone
a
greater
suberin
deposition occurred
in
the
NP,
which
resulted
thicker
and
better

structured
when
compared
to
the
susceptible
clone.