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Helping reduce vegetable ‘transplant shock’

December 22, 2009  By By Paul Schattenberg Texas A&M communications specialist

Dec. 22, 2009 – Dr. Daniel Leskovar, a plant physiologist at the Texas AgriLife Research
and Extension Center in Uvalde, has been investigating ways to help vegetable
plants make a less stressful transition from the greenhouse to the field.

Dec. 22, 2009 – Dr. Daniel Leskovar, a plant physiologist at the Texas AgriLife Research
and Extension Center in Uvalde
, has been investigating ways to help vegetable
plants make a less stressful transition from the greenhouse to the field.


“This research can aid in the successful production and possibly even the
further profitability of some vegetable crops by producing high-quality, more
adaptive plants that will establish well,” Leskovar said. “It could also enable
some vegetable plants to produce beyond their regular season or succeed within
a stressful growing environment.”

An expert in vegetable physiology, Leskovar said his research has been
“centred in the identification and understanding of plant adaptation mechanisms
to temperature, water and biological stresses as part of an integrated
vegetable cropping system.” He and his collaborators already have been
successful in creating heartier pepper, tomato, watermelon and cantaloupe
seedlings for transplantation.



Research at the Texas AgriLife Research and Extension Center in Uvalde
includes investigating the application of gibberellic acid, or GA, a
growth-stimulating hormone found naturally in plants, on artichokes. GA is used
to help the artichoke plant induce bolting in higher-than-needed temperatures
by mimicking the physiological effects of cold weather on the plants.

Researchers from the Texas AgriLife Research and Extension Centers in
Weslaco and Amarillo, as well as a researcher from the Institute for Adriatic
Crops in Croatia, have joined Leskovar in his efforts.

“Our work has primarily involved modulating naturally occurring growth
regulators in vegetable plants,” Leskovar said. “One of these is abscisic acid,
or ABA, which is a hormone naturally produced by the plant. Abscisic acid
affects the closing of plant stomates and controls plant physiology such as
leaf transpiration,” he said. “The hormone also slows plant growth temporarily,
which is important for producing compact transplants in commercial nurseries.”

In many southern regions of the U.S., high temperatures, dry winds and
rapidly drying soil after planting are detrimental to, or impair the early
growth of vegetable transplants, Leskovar said.

“Results of our previous research suggested abscisic acid was an
effective tool to modulate transplant shoot growth and enhance drought-stress
tolerance of several vegetable species,” he said. “Now our research is being
targeted toward foliar spray application to control growth of mature vegetable
transplants in the greenhouse.”

Leskovar noted vegetable plants often suffer transplant shock because of
an imbalance between water loss through transpiration and water absorption
through the roots, typically causing plant wilting. He added that windy
conditions or high temperatures could accelerate water loss.

“Abscisic acid closes the stomates and reduces water loss through
transpiration, preventing further moisture loss in times of low water

Research efforts to date have shown that external application of abscisic
acid to cabbage, watermelon and pepper transplants had reduced undesirable
excess shoot growth during plant development in the greenhouse environment,
Leskovar said. They also show that its application on pepper, tomato and
artichoke seedlings was superior to that of other commercial “film-forming
anti-transpirants” in improving overall plant water status.

“Practices that reduce plant transpiration have the potential to enhance
stand establishment, thus conserving soil moisture and reducing irrigation
frequency,” Leskovar explained. “Abscisic acid appears to be useful for
conditioning vegetable seedlings to withstand temporary stress from water
deficiency and to improve stand development under stressful field conditions.”

He said vegetable transplants quickly recovered their water potential,
stomatal efficiency and photosynthetic rates, and resumed their growth after a
short period of water stress in response to the external application of the

Leskovar added that the work he and his fellow researchers have been
doing has been supported through the interest of the industry and co-operation
with commercial greenhouses in the Rio Grande Valley and Florida.

“Another aspect of our current research is investigating the application
of gibberellic acid, or GA, to artichoke plants so they can produce in Texas,
especially in the late fall,” he said. “Gibberellic acid is a hormone which
stimulates growth and is found naturally in plants, including artichoke and
other vegetable species.”

For the past several years, Leskovar has been investigating the viability
of growing artichokes as an alternative crop in parts of Texas. He and South
Central Texas producers, including some in the state’s Winter Garden area, have
been growing and assessing several varieties of green and red artichokes.

Artichokes are normally planted in late fall, so earlier planting can be
a hit-or-miss proposition for Texas, especially South and Central Texas,
because the plants require successive days of low temperatures to trigger
bolting and produce the edible head, Leskovar explained.

“We can mimic the effects of cold weather on the plant by introducing
gibberellic acid as a natural treatment that will fulfill the plant’s
requirement for bolting during warmer-than-needed temperatures,” he said.

Leskovar noted that gibberellic acid is applied during commercial
artichoke production in other parts of the world, particularly during the
summer months.

“We’re using natural compounds that are part of existing plant physiology
to improve vegetables and make them less susceptible to different stress
factors,” he said. “The process isn’t new, but there’s still a lot to learn
about the response mechanisms in plants, the best way and amounts to apply, and
what effect these will have on a variety of vegetables during different stages
of development.”

Leskovar said the research will be useful as part of an integrated
cropping system strategy for developing more stress-tolerant vegetable plants
which can be grown not only in Texas, but also other southern states with
similar environmental and climatic challenges.

Paul Schattenberg is a communications specialist with Texas A&M


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