Download Vine Crops - Great Lakes Fruit, Vegetable and Farm Market EXPO

Great Lakes Fruit, Vegetable & Farm Market EXPO
Michigan Greenhouse Growers EXPO
December 6-8, 2011
DeVos Place Convention Center, Grand Rapids, MI
Vine Crops
Where: Grand Gallery (main level) Room A & B
Recertification credits: 2 (1B, COMM CORE, PRIV CORE)
CCA Credits: PM(0.5) CM(1.0)
Moderator: Phil Tocco, Agriculture & Natural Resources Educator, Jackson Co.
MSU Extension
2:00 pm
Bacterial Diseases of Vine Crops

2:30 pm
Degradable Mulches: Will They Work in Melon Production?

2:50 pm
Vince Lawson, Muscatine Island Research Farm, Iowa State Univ.
The How’s and Why’s of Grafting Melons

3:20 pm
Sally Ann Miller, Plant Pathology Dept., The Ohio State Univ.
Richard Hassell, Environmental Horticulture Dept., Clemson Univ.
Effects of Watermelon Pollenizers on Yield

Josh Freeman, Horticulture Dept., Virginia Tech Univ.
Managing Bacterial Diseases of Vine Crops
Dr. Sally A. Miller
The Ohio State University, Ohio Agricultural Research and Development Center,
Department of Plant Pathology, Wooster, OH, 330-263-3678
There are a number of serious bacterial diseases of vine crops, most of which are seedborne. Bacterial
diseases are very difficult to manage in vine crops in the field, therefore practices that prevent the
establishment of these diseases are critical. Of the most serious diseases, angular leaf spot, Xanthomonas
leaf spot, and watermelon fruit blotch are seedborne, while bacterial wilt is vectored by cucumber beetles.
Yellow vine decline is a sporadically occurring bacterial disease of vine crops that is transmitted to plants
by squash bugs.
Bacterial leaf spot. This disease is caused by a species of Xanthomonas, and has become a serious
problem in some pumpkin-growing areas in the Midwest, but the disease can also cause significant
damage on other vine crops. Lesions on the leaves range from small and irregular to large and angular.
Centers become necrotic and lesions are surrounded by a chlorotic halo (Fig. 1A). Leaf marginal necrosis
can also occur. Lesions on fruit are raised and scabby, and often on the top of the fruit (Fig. 1B). Flat,
watersoaked areas on fruits may also be observed (Fig. 1C). Spotted
A
B
C
Figure 1. Bacterial leaf spot on pumpkin leaf (A); raised, scabby spots on fruit (B); watersoaked lesions on fruit (C).
Bacterial fruit blotch. Bacterial fruit blotch is caused by a pathogenic bacterium (Acidovorax avenae
subsp. citrulli). This is mainly an economic disease of watermelon, although other vine crops can be
affected. Symptoms on leaves are often inconspicuous. On seedlings, watersoaked lesions on the
underside of the cotyledons become necrotic. The typical symptom of fruit blotch is a dark olive green
spot on the upper surface of the fruit. The spot starts small but rapidly increases in size to cover the most
of the fruit surface within approx. 10 days. Secondary microbes then invade and result in fruit rotting.
Angular leaf spot. Angular leaf spot is caused by Pseudomonas syringae pv. Lachrymans, a bacterial
plant pathogen that is favored by cool, wet conditions. It is a very serious problem in cucumbers and
other vine crops. Symptoms on leaves include angular necrotic lesions surrounded by a chlorotic halo
and sunken spots on fruit. This spots begin a small watersoaked lesions that expand on the surface and
also extend well into the fruit, eventually reaching the seeds.
A
B
Figure 2. Angular leaf spot lesions on a pumpkin leaf (A) and infection of cucumber fruit (B).
Bacterial wilt. This disease is often observed on sunny days after vines begin to run. Individual leaves
begin to droop or flag (Fig. 3A), but the plant recovers at first (see OSU Fact Sheet HYG-3121-96;
http://ohioline.osu.edu/hyg-fact/3000/3121.html). Eventually the vine wilts and the entire plant dies.
Cucumber and cantaloupes are often affected, but squash, pumpkins and less often, watermelon, are also
attacked. This disease is caused by Erwinia tracheiphila and is moved from plant to plant by striped (Fig.
3B) and 12-spotted cucumber beetles. In the spring, the beetles emerge from the ground and feed on
young plants, introducing bacteria into the leaves or stems and spreading the pathogen from plant to plant.
The bacteria reproduce in the water-conducting vessels, producing gums that interfere with water
transport. A diagnostic test for bacterial wilt is the observation of sticky ooze between cut pieces of stem
after touching them together then gently pulling them apart (Fig. 3C).
A
B
C
Figure 3. Young pumpkin plant with early bacterial wilt symptoms (A); striped cucumber beetle (B);
bacterial ooze test (C) to confirm diagnosis of bacterial wilt.
Bacterial Disease Management Steps
Bacterial diseases generally can’t be controlled once they are established in a field and weather conditions
are favorable. Therefore prevention is critical, from seed purchase through field production.
1) Purchase seed that has been tested and shown to be negative for seedborne bacterial pathogens.
This is not a guarantee that plant pathogenic bacteria are absent since low populations may be
undetectable. However, using tested seed is the first line of defense against bacterial diseases.
Some seed companies advertise partial resistance in some varieties to angular leaf spot.
2) If seed has not been tested, consider seed treatment with hot water. This is somewhat risky since
in large-seeded vegetables germination may be reduced. The following method is suggested by
researchers in Australia (R. G. O’Brien and Christine Horlock, Agency for Food and Fibre
Sciences, Horticulture):
If seed has not been rated disease free, an effective seed treatment has been developed. Both
internal and external contamination can be eliminated by soaking seed for 25 minutes in a water
bath maintained at 55 °C. After treatment, place seed in running tap water to bring the
temperature down quickly, then dry seed without delay. Seed should be sown within 2 days. Note
that this treatment may lower the germination of some seed lots. Test a sample before
committing large quantities of expensive seed.
3) Do not over-water seedlings in the greenhouse; try to keep the tops as dry as possible. Minimize
touching and handling the plants. Scout seedlings for small, water-soaked spots; if water-soaked
spots are observed, send a sample to a reputable lab for diagnosis. If bacterial disease is
confirmed, throw away all flats containing symptomatic seedlings. Apply copper-based
fungicides to seedlings in the greenhouse.
4) For field production, select growing sites with good drainage and airflow, full sunlight and low
humidity.
5) Avoid overhead irrigation to prevent leaf wetness.
6) Insure adequate, but not excessive fertility.
7) Protect plants from cucumber beetle feeding at least until the 4th true leaf stage to reduce the risk
of bacterial wilt. Floating row covers can provide a barrier between plants and the beetles that
carry the bacteria. The covers also protect plants from squash bugs that may transmit the yellow
vine decline pathogen. Foliar applied insecticides may also be used – for pumpkins insecticides
should be applied after seedling emergence if the threshold of 0.5 beetles per plant at the
cotyledon stage or 1 beetle per plant at the 1st or 2nd leaf stage is exceeded. Pre-plant insecticide
application (seed treatment or in-furrow) is also effective.
8) If early in a disease epidemic, removal of infected plants may help to slow the spread of disease.
When doing this, make sure not to spread the disease by hand or infested equipment. Diseased
plants must be burned (depending on local ordinances) or buried. Cull piles only serve to spread
diseases.
9) Spray plants with copper-based fungicides to slow progress of the disease.
10) Destroy foliage and vines as soon as possible after harvest to help manage yellow vine decline.
Evaluating Degradable Mulches for Muskmelon Production
Vince Lawson, Muscatine Island Research Farm, Iowa State University
111 North St., Fruitland, Iowa 52749
[email protected]
Introduction
Plastic mulches can provide vegetable growers with earlier crop maturity, better yields and quality,
improved disease, insect and weed control, and more efficient fertilizer and water use. However, a
downside to using plastic mulches is the rather high cost of removal and disposal at the end of the season.
One solution to this problem has been the development of degradable mulches that can be left in the field
after harvest to break apart and disappear. Unfortunately, mulch performance hasn’t always met
expectations. Currently, there are different ways and means of making degradable films creating
questions for growers concerning which one is best for their operation. The objective of this study was to
evaluate three different types of degradable mulches for ease of use, speed of breakdown and how they
influence transplanted muskmelon performance.
Materials and Methods
The degradable mulches included in this evaluation were a 0.6 mil clear and a 0.6 mil black
biodegradable mulch (trade name BioTelo) from Dubois Agrinovation, Quebec, Canada; a 0.9 mil clear
and a 0.9 mil black photodegradable mulch from Poly Expert Inc., Quebec, Canada; and a 0.4 mil clear
and a 0.5 mil black oxo-biodegradable mulch from Eco-One, Ontario, Canada. All mulches were 4 ft
wide. Mulch treatments were laid in the field on April 25 using a Rain Flo raised bed mulch layer. Trial
design was a randomized complete block with three replications. A plot consisted of a single row of
mulch 50 ft long. Muskmelon plants, cultivar Aphrodite, were transplanted on May 18 using a Holland
pot transplanter capable of planting through mulch. Weed control was achieved by applying Prefar
herbicide to beds before laying mulch and applying Strategy and Sandea herbicides between the beds
after laying the mulch. Normal cultural practices were followed for irrigation, fertilization and pest
control. Mulch strength (puncture resistance) was measured once a month with a Chatillon digital force
gauge. Mature muskmelon fruit were harvested during July 21 through August 8 to determine effect of
mulch on early and total yield.
Results and Discussion
The biodegradable (0.6 mil) and the oxo-biodegradable (0.5 mil) mulches were noticeably thinner than
the photodegradable (0.9 mil) mulches. Because of their thinness, and possibly because of their
composition, they were quite fragile and difficult to install in the field, or transplant on, without tearing or
puncturing. In fact, we couldn’t use the transplanter’s press wheels without splitting the biodegradable or
oxo-biodegradable films. The thicker and stronger photodegradable mulches were similar to conventional
mulches and used without difficulty.
All the black mulches provided good weed control but weeds grew thickly under the clear mulches even
though herbicide was used, possibly because of field location and weather conditions. When the sun did
shine weeds under the clear photodegradable mulch became burnt and stunted due to high temperatures
under the mulch. But the clear biodegradable and to a lesser extent the clear oxo-biodegradable didn’t trap
the heat under the mulch due to tears and holes allowing the weeds to grow unchecked. Early and total
yield of the clear biodegradable mulch treatment, and the total yield of the clear oxo-biodegradable mulch
treatment, was reduced because of weed competition (Table 1). Special instructions that come with the
biodegradable and oxo-biodegradable mulches recommend they be laid immediately before planting to
get maximum benefit from the mulch before breakup. Regrettably, as it worked out, the mulch treatments
were laid on April 25, but due to weather conditions and time restraints, we weren’t able to transplant till
May 18, about three weeks later. Evidently, this was too long of a time period as they started breaking up
shortly after muskmelon transplanting causing weed problems.
Muskmelon yield data are presented in Table 1. All of the black mulches and the clear photodegradable
mulch produced good total yield. Normally, because of soil warming, clear mulches enhance early season
crop growth and early yield but that wasn’t the case this season. Conditions after transplanting were cool,
cloudy and rainy resulting in slow vine growth on both clear and black mulches. Then toward late June
the weather became hot and sunny resulting in vigorous growth. Under these conditions the clear mulches
didn’t produce early season yields that were any better than the black mulches.
A problem was noted on fruit picked from the black biodegradable mulch plots. By harvest time the black
biodegradable mulch was breaking down and becoming brittle and soft enough that fragments would stick
to the bottoms of the heavy muskmelon fruit where they sat on the mulch. With some effort the fragments
could be brushed off by hand but in large pickings hand brushing wouldn’t be feasible.
A digital force meter was used to determine puncture resistance of the mulches and monitor how fast they
lost their elasticity in the field after installation (Table 2). The clear biodegradable and oxo-biodegradable
mulches gave the weakest readings after field installation and lost strength fairly rapidly. The readings
also found that the buried edges of the black and clear photodegradable mulches still had good elasticity
and strength in September at the end of the season.
Summary
The photodegradable mulches, because of their strength, were the easiest to use, produced good yields,
but in the fall after disking, left the largest pieces of plastic in the field. The oxo-biodegradable mulches
were thin and fragile making them difficult to work with. However, the black oxo-biodegradable mulch
did provide good weed control and produced a good muskmelon yield. After disking at the end of the
season the oxo-biodegradable mulches left long strips in the field but they were smaller and more brittle
than the photodegradable remnants and aren’t expected to interfere with next season’s field work. The
biodegradable mulches were also fragile and needed careful handling. Due to a delay between mulch
laying and transplanting the clear biodegradable mulch broke up too quickly resulting in severe weed
competition and low muskmelon yield. Note that muskmelon production is an experimental usage as
Dubois Agrinovation recommends the clear biodegradable (BioTelo) mulch be used for early corn
production. The black biodegradable mulch worked reasonably well for muskmelon production except for
the small fragments that would stick to the bottom of the fruit at harvest. To their credit, the
biodegradable mulches were, by far, the best looking at the end of the season in terms of breakdown and
disappearance. After disking in September all that remained were small brittle pieces.
Table 1. Aphrodite muskmelon early and total yield by mulch treatments.
Early
Number
Fruit wt
Number
Mulch treatment
fruit/acre
Cwt/acre
lb
fruit/acre
Clear photodegradable
1864
106.6
5.8
5900
Clear oxo-biodegradable
1760
101.2
5.6
5072
Clear biodegradable
104
4.8
4.7
2277
Total
Cwt/acre
351.8
286.1
119.0
Fruit wt
lb
6.0
5.7
5.2
Black photodegradable
Black oxo-biodegradable
Black biodegradable
1967
2070
1035
109.8
126.8
66.9
5.7
6.0
6.3
5796
6417
5279
335.4
399.0
342.1
5.8
6.3
6.6
Trial Mean
LSD 0.05
1467
861
86.0
52.4
5.7
0.9
5123
1427
305.6
76.1
5.9
n.s.
Table 2. Mulch strength readings in lbf (pound-force) required to puncture. All readings taken from top of
mulch bed except for September 10 readings in parenthesis which were taken on buried edges.
Mulch treatment
May 10
June 10
July 10
August 10
Sept. 10
Clear photodegradable
1.35
1.12
1.19
0.97
0.87 (1.33)
Clear oxo-biodegradable
0.39
0.29
0.23
0.15
0.14 (0.24)
Clear biodegradable
0.45
0.23
0.14
0.03
0.05 (0.17)
Black photodegradable
Black oxo-biodegradable
Black biodegradable
0.95
0.61
0.49
0.91
0.57
0.39
0.81
0.56
0.33
0.57
0.39
0.11
0.48 (0.87)
0.33 (0.40)
0.09 (0.36)
The How’s and Why’s of Grafting Melons
Richard L. Hassell
Clemson University, CREC, 2700 Savannah Highway, Charleston, SC 29414
Introduction
Vegetable Grafting is most common in European and Asian countries where crop rotation
is no longer an option and available land is under intense use (Lee, 1994). Grafting is an
alternative approach to reduce crop damage due to soil borne pathogens and increase plant abiotic
stress tolerance which increases crop production (Cohen et al., 2007). We discuss and outline four
grafting methods that are available for vegetable production in cucurbits; approach graft, hole
insertion graft, one cotyledon graft and the side graft.
History of graft methods
The initial grafting method used for cucumber was cleft grafting (Ishibashi, 1959), but
after the introduction of approach grafting, this technique became widespread in Japan because of
its higher success rate and the uniform growth of grafted seedlings. In Italy the most common
have been the approach and cleft methods (Bianco, 1990; Morra, 1997; Buzi, 2002) but currently
the one cotyledon method and the hole insertion methods are used (Amadio, 2004). A high
proportion (in Spain more than 90%) of watermelon plants are grafted using the one cotyledon
method (Miguel and Maroto, 2000). In France both the side insertion and the approach grafting
have been used in cucumber (Brajeul et al., 1998). Top Insertion Grafting is the most popular
method used in China, since it is suitable for Lagenaria and inter-specific squash as rootstocks
and requires few materials, has a high efficiency, 1,500+ plants/day/worker, and simpler
management requirements.
Manual grafting
There are two methods of grafting, manual and machine. In manual grafting, the grafting
and post-grafting operations require three to four people, each assigned to a specific step in the
process (Lee and Oda, 2003). Cucurbits are usually grafted once the first true leaf appears but
before it reaches full development both in the rootstock and scion seedlings. In order to reach this
stage for both the scion and the rootstock, planting dates will vary depending on the rootstock
chosen. Uniformity in both germination and growth of the rootstock and scion are critical to the
grafting survival. Different grafting approaches have been adapted depending on scion and
rootstock purpose, grafting technique, farmers’ experience, and post grafting management
condition. Approach (tongue graft), hole insertion and one cotyledon grafts (Slant graft) are the
current preferred methods. Modifications to these methods have been done by growers adapting
to there particular operation. The approach technique, which have high survivor rate in general,
and are chosen by non-experienced farmers who are looking into grafting for the first time, have
plenty of space, and adequate labor. One cotyledon and hole insertion grafts require specialized
tools and a healing chamber for a high survivor rate and require time to learn. In addition the graft
junction needs to be above ground during transplanting to avoid the direct contact between scion
and soil since the grafted plants are susceptible to soil born disease if the adventitious root
reaches the ground.
Automatic (machine driven) grafting
The first semiautomatic grafting system for cucumber was commercialized in 1993 and
multiple others have been developed since then, a simple grafting machine can produce 600 grafts
per hour with 2 operators as compared to manual grafting making about 1,000 grafts per person
per day (Suzuki et al., 1998; Masanao and Hisaya, 1996; Lee and Oda, 2003). In Spain the
automated methods represents less than the 5% of the total but may be as high as 10% in Japan
and China. Machine grafting is done using a simple machine or a grafting robot which is
expensive. This also requires highly uniform seedlings to increase the grafting efficiency. New
machines are currently being developed in Japan and Korea that are much more forgiving and
require less labor to operate. The technique used by these machines is the one cotyledon graft. It
is well adapted for machine operation and has a high rate of success. However, they cut the
hypocotyls off the rootstock at ground level as part of the grafting procedure. The hypocotyl is
cut near the root to induce root growth. The increased production of primary roots enhances the
plant’s tolerance to cold and heat and ensures vigorous growth. However, this added procedure
needs an exclusive grafting facility and it is more dependent on the condition of the soil. At
present, 40 percent of watermelon grafting in Japan is done by this method (Suzuki et al., 1998;
Masanao and Hisaya, 1996; Lee and Oda, 2003).
Material and Graft Methods
Quality seed and proper plant growth procedures of both rootstocks and scion material
are critical for grafting to be successful. High quality seed with a uniform germination is a must
at a first step. If primed seed is available take advantage of it. Rootstock seed is generally sown
five to seven days prior to scion in cell trays or germination beds. Scion is sown in trays or
germination beds following the germination requirements of the seeds. The cotyledon of
rootstocks should be fully expanded when the scion emerges, keeping the scion at low relative
humidity before grafting can minimize microorganism problems. Watermelon scion are
harvested (1 or 2 days) after they emerge, are rinsed with clean water, treated with fungicides or
disinfectant, e.g. Physan 20 or peroxyacetic acid/ hydrogen peroxide, to minimize the
microorganism damage to the grafting. There are many requirements for cucurbit rootstock. The
compatibility between rootstock and scion should be high and stable. The rootstock should have
good tolerance to abiotic stress, resistance to soil born diseases, and not negatively affect fruit
quality. In general, grafting compatibility is related to taxonomic affinity. Luffa and melon have
higher compatibility with nettle melon compared to Chinese pumpkin and waxgourd (Wei et al.,
2006). Grafting incompatibility can occur at early stage as vascular connection can not form
properly after grafting. Grafting incompatibility can be delayed until fruiting stage, when
massive nutrition and water are needed. Grafted plants declined early and successful harvesting is
impossible. Incompatibility is less of a problem for those crops, e.g., cucumber and summer
squash, which are harvested with immature fruits. There is positive correlation between the vigor
of grafted watermelon and the similarity of protective isozymes, e.g., peroxidase and superoxide
dismutase, between grafted and regular seedlings (Zhang et al., 2006).
The age of rootstock and scion also plays an important role in compatibility. Optimal seedling
age varies for species and different grafting methods. If seedlings are too young, they are too
tender to handle during grafting process and to old may cause un-wanted meristematic re-growth
tissue.
Once the grafting has taken place, the proper healing chamber in needed to insure
complete union has taken place. Some nurseries producing grafted plants have chambers to
maintain temperature above 20 ºC in the tongue method and around 25 ºC. Air humidity (RH) is
maintained between 85% to 100% (Miguel, 1997). Most nurseries acclimate in small plastic
tunnels inside the greenhouses where it is possible to maintain a high RH (above 85%). Shading
is often required during summer months. 6-8 days after grafting, plants are acclimated to the
natural conditions of the greenhouse buy slowing dropping the humidity. The best conditions for
grafting to take: temperature 22 – 28 OC, RH close to 100%, very low light intensity for the first 5
– 7 days (Miguel, 1997). Humidifiers can be purchased, however, remember that to much free
water can lead to disease pressure and loss of graft union. A fog or mist is the preferred method.
Listed below are the standard procedures used in each of the grafting types currently used
today. These procedures for each method are provided by D. Liere (Syngenta Seeds Inc., 2007)
1. Approach graft. (Tongue Graft)
-Scion seeds should be sown 7 days before rootstock seeds are sown. 242-cell tray is used for
both.
-After rootstock has fully developed cotyledons and scion has cotyledon and first true leaf,
plants are pulled out from the tray and laid on a table (Note: 1 day before doing the grafting,
trays should be watered heavily).
-Do an angle cut into the hypocotyl of rootstock approximately half way with a razor blade, and
make an oppositely angled cut on the hypocotyl of scion. These cuts need to be made so that the
scion will be on top the rootstock when completed.
-Two cut hypocotyls are placed together, then sealed with aluminium foil to help healing and
preventing the graft from drying out.
-The two plants are transplanted into a 72-cell tray, and tray is watered heavily until soil is
completely wet. Trays should then be moved into a greenhouse (Note: After trays have been
placed in the greenhouse water only as needed).
-The top of the rootstock is cut off 5 days after grafting, and the bottom of scion is cut off 7
days after the top of the rootstock is removed.
-After the bottom of the scion is cut off, must wait 2 days for the plants to be ready to
transplant.
-Grafted plants are maintained in the greenhouse until the plants are ready for transplanting. Do
not need a humidity chamber. (Recommendation: Plants should not be older than 33 days before
transplanting).
2. Hole insertion graft.
-Scion seeds should be sown 7 days before rootstock seeds.
- Rootstock seeds are sown in a 72-cell tray. Scion seeds are sown in 242-cell tray. Trays for
rootstock should be watered very well and trays for triploid scion should be watered to the best
moisture for germination. Trays are maintained at 80 °F for germination.
- When both cotyledons and first true leaf start to develop, the rootstock plant is ready to graft
(about 10 days after sowing). Remove growing point with a sharp probe, and then open a slit on
upper portion of the rootstock hypocotyl.
- Scion is angled cut on hypocotyl, and then inserted into the slit on the rootstock.
- Two cut surfaces are matched together and held with a grafting clip.
-Grafted plants should be maintained at 77 °F and 100 % humidity in a growth room. Keep the
plants in the dark for 3 days (after the third day, keep plants in the growth chamber for one more
day with the lights on) before moving them into the greenhouse.
-After moving from growth chamber, grafted plants are maintained at 70-85 °F in the
greenhouse until scion is connected well with the rootstock (Recommendation: Plants should not
be older than 33 days before transplanting).
3. One cotyledon graft. (Slant Graft)
-Scion seeds should be sown 7 days before rootstock seeds.
-Rootstock seeds are sown in 72-cell tray. Scion seeds are sown in 242-cell tray. Trays for
rootstock should be watered very well and trays for triploid scion should be watered to the best
moisture for germination. Trays are maintained at 80 °F for germination.
-When both cotyledons and first true leaf start to develop, the rootstock plant is ready to graft
(about 10 days after sowing).
-One cotyledon with the growing point is cut with a razor blade following the angle of the leaf
petiole. The hypocotyl of the scion is cut in opposite angle.
-Two cut surfaces are matched and held together with a grafting clip.
-Grafted plants should be maintained at 77 °F and 100 % humidity in a growth chamber, and
keep the plants in the dark for 3 days (after the third day, keep plants in the growth chamber for
one more day with the lights on) before moving them into a greenhouse.
-After moving from growth chamber, grafted plants are maintained at 70-85 °F in the
greenhouse until scion is connected well with the rootstock (Recommendation: Plants should not
be older than 33 days before transplanting).
4. Side graft.
-Scion seeds should be sown 7 days before rootstock seeds.
- Rootstock seeds are sown in 72-cell tray. Scion seeds are sowed in 242-cell tray. Trays for
rootstock should be watered very well and trays for triploid scion should be watered to the best
moisture for germination. Trays are maintained at 80 F for germination.
-When both cotyledons and first true leaf start to develop, the rootstock plant is ready to graft
(about 10 days after sowing). A slit is cut on the hypocotyl of rootstock with a razor blade. An
angle cut is done on the hypocotyl of the scion, and then inserted into the slit in the hypocotyl of
the rootstock.
-Two cut surfaces are matched together and held with a grafting clip.
- Grafted plants should be maintained at 77 °F and 100 % humidity in a growth chamber, and
keep the plants in the dark for 3 days (after the third day, keep plants in the growth chamber for
one more day with the lights on) before moving them into a greenhouse.
-The top of the rootstock is cut off 5 days after grafted plants are moved from high humidity
growth chamber. Plants are maintained in the greenhouse until scion is connected well to the
rootstock (Recommendation: Plants should not be older than 33 days before transplanting).
Effect of Special Pollenizers on Watermelon Yield
Josh Freeman, Department of Horticulture, Virginia Tech Eastern Shore Agricultural Research and Extension Center
33446 Research Drive, Painter, Virginia 23420
[email protected]
Over the last decade the popularity of seedless watermelon has increased greatly and now
occupies most of the U.S. market. When growers transfer acreage to seedless watermelon production,
they must take into account that triploid (seedless) watermelon plants do not produce enough viable
pollen to pollinate themselves. Diploid (seeded) cultivars can provide the pollen for the triploid cultivar.
To achieve optimal yields, 20% to 33% of the plants in the field should be diploid. Traditionally,
dedicated rows have been set aside for seeded cultivars within the field of seedless watermelons. A wide
range of pollenizer cultivars have now been designed to be planted in-row between triploid plants. By
eliminating dedicated row space in the field for pollenizers, the number of triploid plants and watermelons
harvested per acre should increase. These pollenizer cultivars are relatively new and the concept itself is
new. Nearly all pollenizer cultivars available have thin vines that have a high degree of lateral branching
and reduced foliage. The most important characteristics of these cultivars are: 1. proliferation of male
flowers and pollen, 2. non-competitive growth habit, 3. and distinct fruit size or rind pattern. It is
important that the cultivars have high numbers of male flowers throughout the season in order to provide
adequate pollen for fruit set in the triploid crop. One of the greatest drawbacks to using special pollenizer
varieties is the cost of the seed, which is generally 3 times that of hybrid diploid watermelon seed. There
is also no return gained directly from special pollenizer varieties because they do not produce marketable
fruit. There has been interest among growers to reduce input costs by using standard seeded varieties inrow, much like special pollenizer varieties would be used.
Previous research has indicated that there are significant differences in flower production between
special pollenizer varieties and standard diploid varieties. There are also experimental results that have
shown a decreased seedless watermelon yield when a standard diploid cultivar was used as a special
pollenizer. However, other experimental data indicates that seedless watermelon yield is not reduced in
this situation. Some research has also indicated that standard diploid varieties used as in-row pollenizers
may reduce seedless watermelon yield through competition while special pollenizer varieties do not.
Another factor that could contribute greatly to the productivity of the seedless watermelon production
system is foot traffic during harvest operations. If a standard diploid variety is used in-row and is
intended to be harvested, this may increase foot traffic and subsequent vine damage. Many times, harvest
crews will not harvest seeded and seedless fruit at the same time, so this would lead to an extra trip
through the field for the harvest crew. This would also be the case if a row is dedicated to a standard
pollenizer that is intended to be harvested.
Growers must decide whether the added input costs of special pollenizers are a good investment
for their operation or if they have a significant market for seeded watermelons. Also they must decide if
the added traffic in a field of seedless watermelons are worth the seeded fruit they will gain.
Unfortunately there is no research to quantify the effect of foot traffic on seedless watermelon yield. The
results may also vary from year to year if standard varieties are used in-row based on variations in
growing conditions.
Resources
Freeman, J.H., G.A. Miller, and S.M. Olson. Performance of Selected Diploid Watermelon Pollenizers.
University of Florida IFAS Extension Publication #HS1081. http://edis.ifas.ufl.edu/hs332
Freeman, J.H. and S.M. Olson. Using In-Row Pollenizers for Seedless Watermelon Production.
University of Florida IFAS Extension Publication #HS1079. http://edis.ifas.ufl.edu/hs333