Southeastern U.S. Vegetable Crop Handbook - 2021 - 30

Additionally, grafting can enhance tolerance to abiotic stress;
increase water and nutrient use efficiency; extend harvest periods;
and improve fruit yield and quality in certain cucurbits. There is a
wide array of potential rootstocks: Lagenaria spp. (bottled gourd),
interspecific squash hybrids, wild watermelon, or melon. These
rootstocks can produce vigorous plants with resistance to many
soilborne diseases. However, each rootstock type provides advantages
or disadvantages under certain environmental conditions.
Check with the transplant grower to see which rootstock they
would recommend for your area.
Grafting Methods for Cucurbits. Grafting in cucurbits is the most difficult
to do and continuous practice is needed to be successful. There are
four commonly used methods to date: tongue approach graft, hole insertion
graft, one cotyledon graft, and side graft. Each of these methods are
described in detail in the following publication: R. Hassell, F. Memmott,
and D Liere (2008) Grafting methods for watermelon production in
HortScience. 43(6):1677-1679.
Only one of these methods is currently automated (one cotyledon
graft method). The other three methods are labor intensive.
Remember that grafting is an art that requires attention to detail.
The major concern with cucurbit grafting is the constant threat of
regrowth of the rootstock, which needs to be removed by hand.
Current research by Hassell and Daley at Clemson University has
eliminated any chance of regrowth by destroying the growing point
of the rootstock. You can read about this method by acquiring the
following publications. Additional information can be found at
http://www.graftingvegetables.org:
1. Daley, S.L., J. Adelberg, and R. L. Hassell. 2014. Improvement
of grafted watermelon transplant survival as a result of
size and starch increased over time caused by rootstock fatty
alcohol treatment: part 1. HortTechnology 24(3):343-349.
2. Daley, S.L., W. P. Wechter, and R. L. Hassell. 2014. Improvement
of grafted transplant survival as a result of size
and starch increase over time caused by rootstock fatty alcohol
treatment: part ll. HortTechnology 24(3): 350-354.
3. Daley, S.L., and R. L. Hassell. 2014. Fatty alcohol application
to control meristematic regrowth in bottle gourd and
interspecific hybrid squash rootstocks used for grafting watermelon.
HortScience 49(3):206-264.
Grafting Methods for Tomatoes. There are three primary techniques
used for grafting tomatoes: tongue approach grafting, cleft
grafting, and tube (or clip) grafting. Cleft grafting and tube grafting
are similar in that the shoot of the fruit-producing scion is
completely cut off from its own roots and attached to the severed
stem of the rootstock. The name 'tube grafting' originated because
when the technique was first developed; a tube was used to hold
the shoot and the rootstock together. Clips are now used to make
this graft. Tube grafting is quicker and less complicated to do
than cleft grafting because it only requires a single, straight cut on
both the rootstock and the scion. In addition, because fewer intricate
cuts are involved, this technique can be used on very small
seedlings. Grafting can be performed at various stages of seedling
growth. Grafting at the 2-3 true leaf stage is common. With both
cleft and tube grafting, the newly grafted plants must be protected
from drying out until the graft union is healed. This usually in30
volves
covering the plants with a plastic cover or protecting them
in some type of healing chamber where temperature and humidity
can be regulated. Some method should be employed to reduce
light intensity to the grafted plants for several days after the procedure.
It is critical to increase the humidity in the chamber to
near 100% for the first two days. Humidity must then be reduced
incrementally over the next five days to prohibit the formation of
adventitious roots from the scion and to provide time for the graft
union to heal. Tomato grafts heal quickly and the seedlings can be
acclimated back into the greenhouse after 4-5 days.
With both cleft and tube grafting, it is important that the
diameter of the cut ends (of the scion and the rootstock) match
up perfectly. If the diameter does not match, the graft may not
heal properly, if at all. Rootstock cultivars tend to have different
growth habits than scion cultivars so it is important to grow
a small amount of rootstock and scion seed at first to determine
their growth rate relative to each other. Rootstock cultivars tend to
be more vigorous than scion cultivars. Another critical factor is to
cut rootstock seedlings below the cotyledons. If the cotyledons are
left, they will generate suckers that will compete with the scion
and requiring pruning. For step-by-step instructions, go to http://
graftvegetables.org/.
DISEASE CONTROL IN PLANT BEDS
For the best control of all soil-borne diseases, use a good commercial
plant-growing mix. If this is not possible, use one of the following
procedures:
Preplant. The only practice that ensures complete sterilization
of soil is the use of steam. When steam is used, a temperature of
180°F must be maintained throughout the entire mass of soil for 30
minutes.
Further information on sanitizing equipment, storage houses,
produce and water can be found in Table 3-51.
Seed Treatment. Seed treatment is important to control seedborne
diseases. Use of untreated seed could lead to diseases
in the plant bed which could reduce plant stands or result in
diseased transplants and potential crop failure. See sections
on SEED TREATMENTS in Tables 3-50 and 3-51 for detailed
information on how to properly treat seeds and for materials labeled
for use as seed treatments.
Postplant. Damping-off and foliar diseases can be a problem in
plant beds. To prevent these diseases, it may be necessary to apply
fungicide sprays especially as plants become crowded in plant
beds. Refer to label clear ance before use. The use of sphagnum
moss as a top dressing will reduce damping-off because it keeps
the surface dry. See the section on GREENHOUSE VEGETABLE
CROP DISEASE CONTROL.
SEED STORAGE AND HANDLING
Both high temperature and relative humidity will reduce seed germination
and vigor of stored seed. Do not store seed in areas that
have a combined temperature and humidity value greater than 100
[e.g., 50°F + 50% relative humidity]. In addition, primed seed does
not store well after shipment to the buyer. Therefore, if you do not
use all the primed seed ordered in the same season, have the seed
tested before planting in subsequent seasons.
2021 Vegetable Crop Handbook for Southeastern United States
http://http:// http://www.graftvegetables.org/ http://www.graftingvegetables.org
Southeastern U.S. Vegetable Crop Handbook - 2021

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