Vegetable Grafting: History, Use, and Current

Technology Status in North America

Chieri Kubota1 and Michael A. McClure
Department of Plant Sciences, The University of Arizona, 303 Forbes Building,
Tucson, AZ 85721-0036
Nancy Kokalis-Burelle, Michael G. Bausher, and Erin N. Rosskopf
U.S. Horticultural Research Laboratory, U.S. Department of Agriculture,
Agriculture Research Service, Fort Pierce, FL 34945
Additional index words. automation, controlled environment, cucurbit, methyl bromide, root-knot nematode
rootstock, scion, Solanaceae
Abstract. Grafting of vegetable seedlings is a unique horticultural technology practiced for many years in East Asia to
overcome issues associated with intensive cultivation using limited arable land. This technology was introduced to Europe
and other countries in the late 20th century along with improved grafting methods suitable for commercial production of
grafted vegetable seedlings. Later, grafting was introduced to North America from Europe and it is now attracting growing
interest, both from greenhouse growers and organic producers. Grafting onto specific rootstocks generally provides
resistance to soilborne diseases and nematodes and increases yield. Grafting is an effective technology for use in
combination with more sustainable crop production practices, including reduced rates and overall use of soil fumigants
in many other countries. Currently, over 40 million grafted tomato seedlings are estimated to be used annually in North
American greenhouses, and several commercial trials have been conducted for promoting use of grafted melon seedlings in
open fields. Nevertheless, there are issues identified that currently limit adoption of grafted seedlings in North America. One
issue unique to North America is the large number of seedlings needed in a single shipment for large-scale, open-field
production systems. Semi- or fully-automated grafting robots were invented by several agricultural machine industries in
the 1990s, yet the available models are limited. The lack of flexibility of the existing robots also limits their wider use.
Strategies to resolve these issues are discussed, including the use of a highly controlled environment to promote the
standardized seedlings suitable for automation and better storage techniques. To use this technology widely in North
American fresh vegetable production, more information and locally collected scientific and technical data are needed.
Grafting of herbaceous seedlings is a
unique horticultural technology practiced
for many years in East Asia to overcome
issues associated with intensive cultivation
using limited arable land for vegetable production. According to Lee and Oda (2003),
a self-grafting technique to produce a large
gourd fruit by increasing root-to-shoot ratio
through multiple graftings was described in
an ancient book written in China in the 5th
century and in Korea in the 17th century. The
first record of interspecific, herbaceous grafting as a yield increase and pest/disease control strategy was for watermelon [Citrullus
lanatus (Thunb.) Matsum.& Nakai], using a
squash rootstock (Cucurbita moschata
Duch.), reportedly developed by a watermelon farmer in Japan (Tateishi, 1927). This
watermelon grafting technique was quickly
disseminated to farmers through extension
research programs of regional agricultural
experimental stations in Japan, and then later
into Korea, during the late 1920s and early
1930s. Use of grafted seedlings in commercial vegetable production occurred as early
as the 1930s in Japan for watermelon grafted
on Lagenaria siceraria (Mol.) Standl. (Oda,
2002). Research on grafting cucumber
(Cucumis sativus L.) also started in the late
1920s, but wider commercial applications did
not happen until 1960 (Sakata et al., 2008).

CEAC paper number D-302430-10-07.

We thank the USDA CSREES (Project # 200751102-03822) for partial support.
1
To whom reprint requests should be addressed;
e-mail ckubota@ag.arizona.ed

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For members of the Solanaceae, the first

record was of eggplant (Solanum melongena
L.) grafted on scarlet eggplant (Solanum
integrifolium Poir.) in the 1950s (Oda,
1999). Grafting tomato (Lycopersicon esculentum Mill.) was introduced commercially in
the 1960s (Lee and Oda, 2003). Along with the
rapid development of intensive protected cultivation technologies using high tunnels and
greenhouses, which presumably prevented
farmers from continuing traditional crop rotation, vegetable grafting became a crucial tool
to overcome soilborne diseases and other
pests. In the 1990s, nearly 60% of open fields
and greenhouses in Japan producing muskmelon (Cucumis melo L.), watermelon,
cucumber, tomato, and eggplant were reportedly planted with grafted seedlings (National
Research Institute of Vegetables, Ornamental
Plants and Tea, 2001) and 81% in Korea (1990
data reported by Lee, 1994). Today, over 500
million grafted seedlings are produced annually in Japan (Kobayashi, 2005). One of the
large-scale grafting operations in Japan is
shown in Figure 1.
Although limited information is available,
it seems that grafting of tomato was practiced
at a limited scale in the United States more
than 60 years ago. According to Lowman and
Kelly (1946), grafting tomatoes using jimson
weed (Datura stramonium L.) as rootstock
was practiced for many years in the southern
United States to overcome root-knot nematodes. Isbell (1944) recommended this
method to home gardeners based on their
research conducted from 1935 to 1943 on
grafting tomato, eggplant, and sweet pepper
on selected weeds. Nevertheless, grafting

tomatoes to jimson weed was not introduced

commercially, and apparently disappeared,
presumably as a result of the potential transport of small amounts of alkaloids to the
fruits, as experimentally proved by Lowman
and Kelly (1946), and also because of the
labor-intensive propagation process.
Intensive labor input and resulting high
costs of grafted seedling production have
been issues preventing this technology from
being widely adopted outside of Asia. However, along with the development of efficient
commercial production techniques for
grafted seedlings and the introduction of
new rootstocks with desirable traits compatible with locally selected scions, grafting
technology was introduced to European
countries in the early 1990s (Oda, 2002)
mainly through marketing efforts of international seed companies and through information exchanges among research communities.
The major objectives of using grafted seedlings are: 1) to achieve resistances to soilborne diseases and nematodes; 2) to increase
yield and quality; and 3) to improve the
physiology of plants making them more
adaptable to harsh environments. Consequently, many countries in Europe, the Middle East, Northern Africa, Central America,
and other parts of Asia (other than Japan and
Korea) adopted the technology and the areas
introducing grafted plants increased rapidly
during the past two decades.
Until recently, grafted seedling production and its use were not common in North
America. The exception was the home garden
practice in the southern United States as
described previously, and there have been
HORTSCIENCE VOL. 43(6) OCTOBER 2008

Fig. 1. Grafting operations in Canada (A) and in Japan (B). Each operation has the capacity to produce more than 10 million grafted seedlings annually.

small numbers of organic growers who practiced this technique by themselves to overcome soilborne diseases and pests in their
small operations (M. Peet, personal communication). Recently, along with the success
of European-based, large-scale greenhouse
operations in North America, the improved
yield and fruit quality by using grafted seedlings became known to more growers. The
majority of users of grafted seedlings is
currently greenhouse hydroponic tomato
growers, whereas it is still a relatively
unknown technique for open-field producers.
Recently, several trials in North America
have been initiated using grafted seedlings
for open-field vegetable production. Strong
marketing efforts by seed companies and
genuine interest from practitioners in integrated pest management have driven collaboration with producers, universities, and
other research institutions. The authors currently work as an interdisciplinary team to
develop necessary technologies, collect local
information, and conduct trials in different
climatic zones in the United States considering grafted plants as a means to mitigate yield
losses to pathogens and to partially replace
methyl bromide soil fumigation. In Mexico,
Guatemala, and other countries, similar but
larger-scaled projects led by the United
Nations Industrial Development Organization contributed to disseminating information
on the efficacy of vegetable grafting
(UNIDO, 2007).
CURRENT USE OF GRAFTED
SEEDLINGS
Although estimating the growing number
of grafted plants used in North America is
challenging, surveys conducted by faculty at
the University of Arizona in 2002 and 2006
showed that the total number of grafted seedlings used in North America was over 40
million with the majority of these used in
hydroponic tomato greenhouses. A relatively
small number of grafted watermelon seedHORTSCIENCE VOL. 43(6) OCTOBER 2008

lings were used for trials in open fields (less

than 100,000 plants).
Many of the propagators supplying
grafted seedlings to greenhouse growers are
located in Ontario or British Columbia,
Canada (Fig. 1). These propagators expanded
their business successfully along with the
success of greenhouse tomato growers.
Because there are only small experimental
propagation capabilities in the United States,
large-scale propagators, each with 10
million seedling production capacity in
Canada, are still the major sources of the
grafted seedlings used in the United States
and northern Mexico. Many organic farmers
and growers who produce in small greenhouse operations graft their own tomato
seedlings because there are no local propagators available.
Grafted tomato seedling production and
use. In most propagation operations in North
America, grafting of tomato is accomplished
by using an elastic plastic tube that holds the
graft union cut at an angle (so-called tube
grafting method). Each plastic tube has a slit
so it falls off as the stem expands in diameter.
Grafting speed using this tube grafting
method varies from 300 to 500 grafts per
hour depending on the workers skill
(J. Marie, personal communication). Grafting
is usually performed 2 to 3 weeks after
seeding. Some rootstock seeds exhibit slower
germination and require seeding 1 week
earlier than the scion to develop compatible
stem sizes at the time of grafting. Propagators
need to optimize the seeding schedule for
each selected combination of scion and rootstock so as to maximize the grafting success.
Grafting young seedlings is considered
advantageous as a result of the smaller size
of seedlings, which allows greater seedling
density and reduces the cost. After grafting,
seedlings are placed under high humidity
(greater than 95%), ambient temperature
(27 to 28 C), and low light intensity (100
mmol
m2
s1 photosynthetic photon flux) for
4 to 7 d to heal the grafted union. Many North

American propagators use a humidification

chamber or a simple covered structure inside
a shaded greenhouse, whereas more sophisticated indoor healing units with better air
temperature, relative humidity, and light
intensity control capability are commercially
available in other countries. This is probably
because tomato grafting and healing methods
are relatively easy and tomato is the major
crop currently grafted in North America.
After healing, grafted tomato seedlings
are acclimatized inside the greenhouse and
then often pinched to induce two lateral
shoots. This two-headed grafted seedling
is widely accepted in greenhouse production
systems where it reduces the production cost
while maintaining the yield per head (and
therefore overall yields) (Kubota, 2008;
P. Rorabaugh, unpublished data).
Among the North and Central American
countries, use of grafted tomato seedlings in
open fields seems to be most advanced in
Mexico. After 2 years of successful trials,
tomato producers in Mexico have used
grafted seedlings on 1250 acres (500 ha) to
overcome Fusarium oxysporum f. sp. lycopersici race 3, thereby attracting the interest
of other producers (F. Knol, personal communication). Nevertheless, a recent outbreak
of seedborne bacterial disease in a grafting
trial in Mexico alerted propagators and producers to the seeds and seedlings from unreliable sources. Especially when the available
sources of grafted seedlings and rootstock
seeds are limited and, therefore, grafted seedlings travel a long distance, both propagators
and producers must be cautious to prevent
accidental introduction of diseases and
viruses through transportation of seeds and
seedlings.
Although there are many tomato rootstock varieties available worldwide, currently it seems that only one or two hybrid
tomato rootstock varieties dominate the
North American grafting rootstock market.
This is probably the result of their early
introduction and success in greenhouse

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tomato hydroponic production using the specific vigorous rootstocks. Making other alternative rootstocks available would help
develop long-term strategies for pest and
disease control, particularly for introduction
of grafting into open-field tomato production.
Grafted cucurbit seedling production and
use. Several commercial trials using grafted
watermelon and muskmelon seedlings were
conducted in multiple locations across the
country to increase yield, quality, or to
demonstrate grafting as a potential partial
alternative to soil fumigants. Unlike members of the Solanaceae, in which tube grafting
is the single dominant grafting method,
cucurbit species are grafted using many
different methods, including approach grafting, cotyledon grafting (a type of splice
grafting), cleft grafting, and hole-insertion
grafting (Lee and Oda, 2003). Some propagators use unrooted cuttings as rootstocks
harvested before grafting, and root the
grafted cuttings while the grafted unions are
healed. These nonstandardized procedures
for cucurbit grafting also make technology
transfer challenging in cucurbits. Many
North American propagators still rely on
approach grafting, the slowest but most
assured method for cucurbits.
CURRENT AND FUTURE
TECHNOLOGY NECESSARY TO
WIDELY ADOPT GRAFTING IN
NORTH AMERICA
Wider use of grafted vegetable seedlings
has considerable potential in North America.
However, several issues described subsequently have been identified as major limitations.
Limitation of available rootstock
information. Greenhouse tomato constitutes
more than 90% of grafted seedling production in North America (Kubota, 2008). The
majority of these seedlings are currently
grafted to one or two common rootstocks.
There is only limited information on the use
of other rootstocks, compatibility to open-field
cultivars, and field performance of grafted
seedlings in various climatic conditions.
Resistance information of rootstocks available from seed companies may not necessarily contain all the resistance/tolerance
potentially exhibited in local soil and environmental conditions. One example is the
recent finding that muskmelons grafted to
interspecific hybrid squash (Cucurbita
maxima Cucurbita moschata) had resistance
to vine decline caused by Monosporascus
spp. (Cohen et al., 2000; Edelstein et al.,
1999) and tolerance to charcoal rot (Macrophomina phaselina) (C. Kubota et al., unpublished data).
Other rootstock information missing but
critical in applications to North America is
efficacy over root-knot nematode (RKN)
(Meloidogyne spp.). Many tomato rootstocks
contain the Mi gene and have been incorporated into many tomato cultivars for resistance to RKN as demonstrated using
Beaufort rootstock by Cao et al. (2005). A

1666

drawback of the Mi gene, however, is its

sensitivity to temperature, and failure of
resistance can occur at high soil temperature
(Dropkin, 1969; Williamson, 1998). Nematode isolates capable of breaking Mi resistance have also been identified in many areas
of world (Williamson, 1998). Ioannou (2001)
examined a tomato rootstock for grafting
eggplant and found reduced efficacy of grafting against RKN in summer crops, presumably as a result of the high soil temperature.
More information is needed on the effectiveness of various tomato rootstocks under high
soil temperatures (critical temperatures are
generally above 28 C) (Dropkin, 1969). Wildtype-based tomato rootstocks may have other
resistance genes that are stable at higher soil
temperatures. Such high temperature-resistant genes were reportedly found in Lycopersicon spp. (Williamson, 1998). Therefore,
resistance screening tests need to be conducted at varied temperatures using RKN
species specific to the location in which
grafted plants are to be introduced. Such
information is particularly critical for applying grafting technology in Mexico and the
southern United States, including Florida and
south Texas, to identify overall resistance of
rootstocks to multiple pests and diseases
under subtropical conditions.
To our knowledge, cucurbit rootstocks
with RKN resistance are not commercially
available, but there are a few species that are
promising candidates. Igarashi et al. (1987)
examined several wild Cucumis species,
including Kiwano (Cucumis metuliferus
Naud.), for resistance to RKN and grafting
compatibility to muskmelon. Considering all
aspects, including fruit size and yield, Igarashi
et al. (1987) concluded that C. metuliferus is
the most suitable rootstock exhibiting good
resistance to RKN. Recently, a research
group in California (Siguenza et al., 2005)
reported that C. metuliferus can be used as a
rootstock for muskmelon to prevent both
plant growth reduction and nematode population increases in M. incognita-infested soil.
Siguenza et al. (2005) also found that
C. moschata rootstock, a traditional rootstock
used for cucurbits in Asia, had a high level of
tolerance to M. incognita.
Information on resistance/tolerance of
commercially available rootstocks and
potential germplasm usable for breeding
new rootstocks needs to be collected based
on locally conducted trials and research.
Germplasms that are considered as weeds
elsewhere are sometimes introduced as new
rootstocks. For example, selected lines of
Solanum torvum Swartz (Turkey berry, a
weed widespread in Florida) from germplasm
collected from Puerto Rico and Thailand
have been used for grafting solanaceous
plants in Japan (Takii Seeds, personal communication). The vigorous growth characteristics of S. torvum in various ecosystems is
an attractive feature to introduce for Solanaceae rootstocks. Introduction of biotechnology to rootstock development has been also
attempted by researchers (e.g., Gal-On et al.,
2005).

Limitations of propagators experience

with grafting. The majority of propagators
capable of grafted vegetable seedling production are located in Canada and Mexico.
Currently, U.S. propagators have limited
experience. Furthermore, a limited number
of university extension and research institutions are familiar with the specific techniques
of grafted seedling production. Consequently, many propagators in North America
had to learn grafting technologies from practitioners in countries such as Korea, Spain,
The Netherlands, and Israel.
Limited access to information on the process of grafting seedlings and production
scheduling only available in languages other
than English is an additional issue. A shortage of well-trained propagators with experience in grafted seedling production also
limits wider application in North America.
Education and dissemination of information
through workshops and short courses is important but will reach only a limited number of
stakeholders. The authors are in the process
of developing an informational web site to
reach a wider audience and a larger number
of stakeholders.
Handling large numbers of grafted
seedlings. Another issue unique to North
America is the large number of seedlings
needed in a single shipment. The labor available within a propagation operation will limit
the number of plants available for delivery at
a given time. One solution is the development
of short-term seedling storage techniques,
which can distribute available labor input
for grafting over time while targeting a
narrow shipping window. Tomato and eggplant seedlings can be stored at low temperatures under dim light for up to 4 to 6 weeks
(Kubota, 2003), but storage protocols are not
well developed for cucurbits. Lowering
temperature can slow the respiration and
metabolic processes and thereby prevent undesirable quality degradation. In postharvest
storage, temperature is generally selected to
be the lowest possible temperature that
does not cause chilling injury (CI) to the
produce. For storage of seedlings, avoiding
CI and maintaining photosynthetic and
regrowth abilities are necessary. Both temperature and light environments are important to optimize storability of seedlings
(Heins et al., 1992; Kubota, 2003). Grafting
on chilling-tolerant rootstocks may extend
the storability of the seedlings and therefore
information should be collected for different
graft combinations.
The introduction of mechanization and
automation technology will also help address
large-scale production issues. Efficient labor
management has been recognized as a key
to success in mass production of grafted
seedlings. Semi- or fully-automated grafting
robots were invented by several agricultural
machine industries (Kurata, 1994) and some
models are available in East Asia, Europe,
and more recently in the United States.
According to Kobayashi (2005), the first
commercial model of a grafting robot
(GR800 series; Iseki & Co. Ltd., Matsuyama,
HORTSCIENCE VOL. 43(6) OCTOBER 2008

Japan) became available for cucurbits in

1993 and there were various semi- and fully
automated grafting robots presented from
nine different agricultural machine industries
at an international horticultural trade show in
Tokyo in 1996. Kobayashi (2005) also noted
that grafting robots were developed in other
countries, and a semiautomated system suitable for multiple species, including cucurbits,
members of the Solanaceae, and roses, became available from Arnabat S.A. (Barcelona,
Spain) in 2000. Another semiautomated
grafting robot for cucurbits, similar to Isekis
GR800, was developed in Korea in 2004
(GR-600; Helper Robotech Co., Gimhae,
Korea). For fully automated grafting robots,
in 1994, Yanmar Agricultural Equipment Co.
(Osaka, Japan) introduced an AG1000 robot
for grafting solanaceous plants based on a
128-cell tray system, in which an entire row
of eight seedlings could be grafting at one
time, achieving a speed of 1200 grafts per
hour with one assisting operator. Unfortunately, many of these grafting robots introduced to commercial propagators in the late
1990s and the early 2000s are underused in
operations. Kobayashi (2005) pointed out
several issues, including challenges in producing scion and rootstock seedlings that
consistently meet the size and quality specifications required by grafting robots. Along
with internationalization of grafting technology and emerging demand from counties like
the United States where labor management is
a significant issue in agriculture and horticultural operations, improving grafting robots
and seedling production technology adoptable to automation is an immediate need.
Several groups of researchers and engineers
in Japan currently work on improvement of
the relatively old grafting robot technology or
on development of more flexible grafting
robots. One such effort is a fully automated
grafting robot for cucurbits, which was
recently developed based on the 1993 version
of Isekis GR800 semiautomated robot
(K. Kobayashi and K. Shigematsu, personal
communication). The prototype model (Fig.
2) has scion and rootstock feeders, which
pick, orient, and feed the scion and the
rootstock shoots to the grafting processor,
performing 750 grafts per hour with a 90%
success rate. The new robot will be commercially available in a few years.
High production costs. Our recent survey
found that the price of tomato seedlings for
fresh market tomato production is currently
$0.03 to $0.40 per seedling (excluding seed
costs), whereas the current price of grafted
melon and tomato seedlings is $0.60 to $0.90
in addition to seed costs. The high cost of
grafted seedlings is the result of intensive
labor input for propagation, a longer production period, and the additional costs of the
rootstock. Those expenses often discourage
potential users of grafted seedlings. Not often
acknowledged is that growers may be compensated for the greater initial cost of buying
grafted seedlings by additional benefits of
increased yield and reduced cost of control
measures for soilborne pests. According to
HORTSCIENCE VOL. 43(6) OCTOBER 2008

Fig. 2. A prototype of a fully automated grafting robot for cucurbits with a capability of 750 grafts per hour
(courtesy of BRAIN, Saitama, Japan).

the EPA (1997), fumigation with methyl

bromide costs $0.41 to $0.92 per plant,
almost comparable to the current cost for
buying a young grafted seedling produced in
Canada ($0.90 per a double-headed plant
or $0.45 per head), although the cost of the
grafted plant does not account for other pest
control tactics such as effective herbicide
packages required in the absence of methyl
bromide. Further investigation and economic
analyses are necessary taking local economic, agronomic, and pathologic situations
into consideration. The University of Arizona
also conducted a yield comparison in tomato
and found an increase of 15% when grafted
plants were compared with nongrafted seedlings in both a greenhouse (P. Rorabaugh,
unpublished data) and in a small field trial
with low disease pressure (C. Kubota, unpublished data). It may be possible to pair
grafting with effective, site-specific herbicide
packages to accomplish production with
yields similar to those achieved in open-field
production using soil fumigation, which
would give growers an incentive to use
grafted seedlings.
Long-distance transportation. As a result
of the limited availability of grafted
seedlings, greenhouse tomato growers often
purchase grafted seedlings from distant
propagators, risking deterioration of transplants during transportation and the consequential delayed growth or fruit development
(Kubota and Kroggel, 2006). It has been
observed that lower temperatures and illumination significantly maintained transportability of the seedlings. For mature tomato
seedlings at flowering stage, simulated transport at 6 to 13 C showed the best transport-

ability without experiencing negative impact

for the 4-d simulated transportation. Seedlings at 18 C exhibited serious quality
deterioration, delay in early season growth
and development, loss of flower buds on the
first truss, and yield reduction (Kubota and
Kroggel, 2006). Transportation conditions
need to be modified according to plant
growth stage and plant quality at the time of
transportation. Air freight is an alternative
transportation means for smaller seedlings
and plugs but has less flexibility in controlling temperature than refrigerated trucks.
Trailers temperature can be selected to prevent CI while minimizing the physiological
deterioration of plants resulting from excessive respiration and ethylene accumulation
during transportation. The vapor pressure
inside trailers is generally very close to
saturation (100% relative humidity) as a
result of the floor-to-ceiling loading of seedlings. This high humidity sometimes causes
rapid spread of disease. Damage to grafted
seedlings resulting from an unpredicted event
such as an unanticipated prolonged duration
of transportation or disease epidemic could
result in a long-term impact on plant growth
and yield.
New controlled environment technology.
One critical item necessary for successful
grafted seedling production is uniformity of
seedlings used for scion and rootstock. One
way to improve the uniformity is the use of
automatic sorting machines equipped with a
machine vision system as successfully used
in Europe and Canada. Another approach is
the use of production systems under artificial
lighting. The latter can contribute to the
ability to manipulate production scheduling.

1667

Fig. 3. High-quality seedlings with uniform size suitable for grafting produced under artificial lighting
(white fluorescent lamps) inside a closed system. The technology has been adopted by commercial
propagators in Japan.

As a result of the relatively short duration of

each growth stage of grafted seedling production, fluctuations in weather can often
change the entire production schedule, and
shipping schedules must be adjusted accordingly. As a result of a short production cycle
and the consistent seedling quality, use of
artificial environments to produce grafted
seedling plugs can be feasible, especially
for mass production systems. The advantages of using an artificial environment are
the predictable production schedule and
standardized seedling quality as a result of
the consistent environmental conditions and
therefore plant growth and development.
Production of scion and rootstock seedlings
having a standardized quality will facilitate
use of automation in the grafting process.
Failure resulting from lack of uniformity
among plants is a common cause of ineffective use of grafting robots (Kobayashi, 2005).
Techniques for producing transplants
under artificial lighting have been recently
adapted to commercial propagators after the
successful development of a commercially
available transplant production unit in Japan
(Tsuchiya, 2003) (Fig. 3). Research directed
toward transplant production using artificial
lighting systems under controlled environments was initiated in the late 1980s. Dreesen
and Langhans (1991, 1992) reported that
using such systems was profitable because
of a high value per unit of production area
and a short production time of transplants.
Ohyama et al. (2003) reported that the cost
of electricity for growing tomato seedlings
for 17 d under artificial lighting in a closed
production system with good insulation and
containment will be 116 kWh per each square
meter of production area (equivalent to 2.9 to

1668

3.2 Japanese Yen or $0.03 per seedling grown

in a 128-cell tray). Today, advanced Japanese
commercial propagators successfully use
closed-type production systems with artificial
lighting for growing uniform scion and rootstock seedlings, a critical stage in grafted
seedling production. Closed-type seedling
production systems and automatic grafting
machines should be adopted in North
American grafted seedling production to process a large number of grafted plants with
limited labor. Closed-type seedling production system also has a significant advantage
over conventional greenhouse propagation
if one considers the quarantine and certification demands of importation for out-of-state
or international production of grafted seedlings.
Conclusions
Herbaceous grafting has been practiced for
many years in countries in Asia, Europe, the
Middle East, Northern Africa, and Central
America, and now it has been introduced as
a relatively new technology in North America.
As a result of its benefits and value, demand
for high-quality grafted seedlings by growers
and interest by propagators are expected to
rapidly increase. Researchers, extension specialists, and industries need to work together
to integrate this modernized technology as an
effective tool for sustainable horticultural production in North America.
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