Heirloom tomato cultivars lack genetic
disease resistance and are particularly sus-ceptible
to epidemics in the field. Growers
interested in this niche market, however,
are not willing to give up the high- qual-ity
fruit that they deliver. Grafting can be
used to unite the soilborne disease resis-tance
and enhanced vigor of hybrid to-mato
cultivars with the high fruit quality
of heirloom varieties.
Grafting: An Old Technology
with a New Technique
Grafting vegetables to manage soilborne
disease is a simple process. The below-ground
portion of a plant— the root-stock—
is chosen for its genetic ability to
resist or tolerate soilborne disease. The
above- ground portion of the plant— the
scion— is chosen based on fruit quality.
“ Japanese top- grafting” or “ tube graft-ing”
is a new technique that is especially
popular for tomato production in com-mercial
greenhouses worldwide because
the process is very fast and large numbers
of grafted seedlings can be managed eas-ily
throughout the healing process ( Figure
1). Each seedling is severed just above
the cotyledon. The above- ground portion
( scion) of the heirloom variety is secured
to the root system ( rootstock) of the dis-ease-
resistant seedling. Once the grafted
transplants heal, they can be planted in
the field and managed according to the
grower’s production system.
Although vegetable grafting is rela-tively
new, it relies on an old principle.
Grafting
Grafting has been used in the horticultural
industry for woody species, such as apples
and grapes, for centuries. The first use of
vegetable grafting to reduce soilborne dis-ease
occurred in the early 1900s to dimin-ish
fusarium wilt on watermelons. More
recently, this technique has been used in
plant production systems when the ge-netic
trait for disease resistance in a crop
is closely linked to a negative quality, such
as small fruit size. For example, grafting is
often used to reduce bacterial wilt ( caused
by Ralstonia solanacearum) in tomatoes.
This disease complex is particularly dif-ficult
to manage due to its wide range of
hosts and its ability to persevere through
long crop rotations. In addition, tomato
cultivars that are resistant to bacterial wilt
are typically not capable of producing
large, marketable fruit. The worldwide
use of grafting with resistant rootstock
has significantly decreased bacterial wilt
incidence while keeping fruit quality high,
even in severely infested soils.
Figure 1. Silicon tube- shaped clips are used
for “ Japanese top grafting.”
for Disease Resistance
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May 8 and June 30, 1914.
North Carolina State Uni-versity
and North Carolina
A& T State University com-mit
themselves to positive
action to secure equal
opportunity regardless of
race, color, creed, national
origin, religion, sex, age, or
disability. In addition, the
two Universities welcome
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to sexual orientation. North
Carolina State University,
North Carolina A& T State
University, U. S. Department
of Agriculture, and local
governments cooperating.
Grafting is a simple technique that growers
can use to increase soilborne disease resistance
in tomatoes without chemical fumigants or pesticides.
in Heirloom Tomatoes