Improved
maintenance
of
the
tomato
-
like
Solanum
spp
.
by
grafting
Chetelat,
R
.
T
.
and
J
.
P
.
Petersen
C
.
M
.
Rick
Tomato
Genetics
Resource
Ctr
.
,
Dept
.
of
Vegetable
Crops,
Univ
.
of
California,
Davis,
CA
95616
We
have
struggled
over
the
years
to
reproduce
the
tomato
-
like
Solanum
species
our
collection
.
S
.
juglandifolium
is
diffi
in
cult
because
some
accessions
refuse
to
flower
under
our
greenhouse
conditions,
even
during
short
-
day
regimes
which
induce
other
sensitive
species
.
Its
close
cousin
S
.
ochranthum
flowers
somewhat
more
readily,
but
only
after
growing
so
tall
that
it
becomes
difficult
to
handle
.
Finally,
the
xerophyte
S
.
sitiens
is
hypersensitive
to
soil
-
borne
fungal
pathogens,
usually
brought
on
by
over
watering
or
transplant
stress
.
As
a
result,
many
plants
succumb
before
seed
can
be
harvested,
resulting
in
inadvertent
selection
and
loss
of
genetic
diversity
in
subsequent
generations
.
Our
repeated
attempts
to
ameliorate
this
problem
by
careful
watering,
applications
of
fungicides,
or
use
of
specialized
soil
mixes
have
met
with
limited
success
.
Each
of
these
challenges
can
be
overcome
by
grafting
the
nightshades
onto
a
tomato
rootstock
.
Rick
(TGC
37:62)
used
L
.
esculentum
cv
.
VF36
as
a
graft
rootstock
to
promote
flowering
in
S
.
juglandifolium
.
However,
during
the
time
it
takes
to
reproduce
this
species
(up
to
~
2
years),
rootstocks
would
eventually
lose
vigor
or
die
altogether
due
to
attack
by
Phytophthora
root
rot
and
other
diseases
.
We
therefore
tested
the
interspecific
hybrid
F
1
L
.
esculentum
cv
VF36
x
L
.
pennellii
LA0716
as
a
potential
graft
rootstock
.
This
genotype
has
several
advantages
for
grafting
applications
.
First,
the
hybrid
is
amazingly
vigorous
in
its
vegetative
growth,
as
anyone
who
has
had
the
misfortune
to
include
it
in
a
field
trial
can
attest
(a
single
plant
will
quickly
overwhelm
rows
on
either
side)
.
Secondly,
the
L
.
pennellii
parent
contributes
dominant
resistances
to
multiple
races
of
Fusarium
wilt
.
As
a
result,
roots
of
the
hybrid
are
either
resistant
to
or
can
‘outgrow’
our
common
soil
-
borne
diseases,
and
plants
can
be
maintained
indefinitely
in
pot
culture
.
Thirdly,
the
hybrid
has
wide
graft
compatibility,
not
only
with
the
Solanum
spp
.
in
question,
but
also
with
more
distantly
related
Solanaceous
crops,
such
as
eggplant
(
S
.
melongena
)
and
pepper
(
Capsicum
spp
.
)
.
Finally,
L
.
pennellii
and
its
hybrid
with
tomato
are
daylength
insensitive,
and
flower
continuously
throughout
the
year,
with
relatively
few
leaves
between
successive
inflorescences
(sympodial
index
=
2
in
L
.
pennellii
)
.
Although
the
hybrid
has
an
annoying
tendency
to
sprout
adventitious
shoots,
these
are
easily
distinguished
from
scion
branches
and
pruned
off
.
Standard
cleft
type
grafts
were
made
when
the
rootstock
was
at
the
~4
-
5
true
leaf
stage,
using
stems
of
roughly
the
same
diameter,
from
each
of
the
three
Solanum
spp
.
Graft
unions
were
wrapped
with
Nescofilm,
and
scion
branches
were
pruned
to
several
axillary
buds,
then
enclosed
in
a
Ziploc
plastic
bag
for
10
-
14
days
.
Only
a
small
proportion
(<10%)
of
grafts
failed
on
the
first
attempt,
generally
due
to
a
poor
match
in
stem
diameter/age,
or
Botrytis
infection
.
Both
graft
partners
recovered
readily
from
wounding,
with
shoots
of
the
Solanum
spp
.
becoming
woody
and
strong,
and
growing
vigorously
.
For
S
.
juglandifolium
(LA2120
and
LA2788)
and
S
.
ochranthum
(LA2166
and
LA2682),
grafts
were
made
starting
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