Granulosa
(
grn
)
a
new
epidermal
trichome
marker
Rick,
C
.
M
.
Department
of
Vegetable
Crops
.
University
of
California,
Davis,
CA
95616
This
mutant
(3
-
804),
induced
by
EMS
in
cv
.
Castlemart,
was
first
identified
in
1981,
contemporary
with
cactiflora
(
ccf
)
.
In
the
initial
M2
the
segregation
was
8
normal
and
one
granulosa,
the
latter
strikingly
distinct,
not
only
for
the
hair
trait
but
also
for
very
retarded
growth
and
chlorosis,
manifest
particularly
in
a
yellow
-
green
virescence
.
The
main
point
of
interest
in
grn
is
the
unusual
modification
of
the
large
epidermal
trichomes
(Luckwill's
type
I)
.
In
the
catalog
of
normal
esculentum
hair
types,
these
large
multicellular
trichomes
are
the
most
conspicuous
.
Their
main
column
or
stem
consists
of
a
series
of
8
-
12
elongate
cells
arranged
end
-
to
-
end,
totaling
2
-
3
mm,
easily
visible
to
the
naked
eye
.
It
surmounts
a
rounded
mound
of
a
few
to
many
cells,
well
detailed
at
low
magnification,
but
well
distinguished
without
magnification
if
differentially
pigmented
with
anthocyanin
as
in
the
pennellii
-
derived
punctate
(
pun
)
mutation
.
The
multicellular
or
"cushion"
bases
of
grn
are
greatly
expanded
--
up
to
1
-
2
mm
in
diameter
(see
illustration
below)
.
The
net
effect
is
a
"granular",
roughened
surface
of
stems,
pedicels,
and
leaf
bases
.
This
trait
alone
serves
to
distinguish
+
from
grn
unequivocally,
but
strongly
reinforced
by
pleiotropic
differences
in
vigor
and
chlorophyll
intensity
.
Segregation
of
a
series
of
M3
families
is
summarized
below:
Pedigree
No
.
Phenotypic
segregation
+
grn
94L666
11
3
667
15
0
668
11
4
669
12
2
670
0
15
671
11
3
672
15
0
In
these
and
other
F2
segregating
families
the
totals
are
69+
:
19
grn
,
deviating
only
slightly
from
the
expected
66+
:
22
grn
.
The
limited
data
are
thus
consistent
with
monogenic
recessive
determination
.
The
seed
yield
of
the
parent
of
fam
.
#670
was
high
enough
to
justify
hopes
that
this
mutant
is
sufficiently
fertile
to
be
a
useful
seedling
marker
.
No
linkage
data
are
yet
available
.
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