What Plants REALLY Want!
The Tomato Magazine
By Don Comis, Agricultural Research Service Information Staff.
The greenhouse manager of the future walks around the greenhouse, pointing
an infrared fl ashlight at potted plants. A tiny screen tells whether
each plant has too much, too little, or just the right amount of nutrients.
The manager doesnt worry about water because he lets a computer
worry about that for him. The computer reads moisture sensors that trigger
irrigations only as needed. The top two concerns of greenhouse operators
are to make sure their valuable plants arent ruined by too little
or too much water and to provide them with optimal nutrients. And these
issues should also be the top two research priorities for Agricultural
Research Service scientists working on commercial greenhouse production.
Thats what ARS plant pathologist Jim Locke and ARS horticulturist
Jonathan Frantz learned a few years ago, after extensive contact with
Ohios booming greenhouse and nursery industry. In 2001, in
response to a congressional initiative, Charles Krause, research leader
of the ARS Application Technology Research Unit (ATRU) at Ohio State University
(OSU) at Wooster, Ohio, formed a team to research ways to overcome priority
problems faced by the fl oricultural greenhouse industry in the Great
Lakes region, to make American producers more competitive globally.
In 2002, Locke relocated to Toledo, Ohio, from the Henry A. Wallace Beltsville
(Maryland) Agricultural Research Center. Six months later, Frantz joined
him there. By 2003, the ARS Greenhouse Production Research Group (GPRG),
a worksite of ATRU, was fully operational, working to shape the industrys
automated future. The group operates out of a complex of labs, offices,
and greenhouses on the University of Toledos main campus. It also
leases about 8,000 square feet of greenhouse space from the nearby public
Toledo Botanical Garden. The garden provides ARS and university researchers
with meeting space for grower focus sessions and offers expertise in transferring
research information to growers. The garden also houses 18 county horticulture
organizations, including OSU Extension, Urban and Consumer Horticulture,
the Master Gardener Volunteer Program, and Green Industry Education.
Scoping Out the Industrys Needs
At the very beginning, Locke and Frantz toured greenhouses throughout
northern Ohio to talk with industry people about priority problems and
to observe the operations themselves. When we made a short list
of the top problems that could be researched to fi nd solutions, we realized
that all of them had nutrition or water as a common theme, Frantz
says. So we made those the top research areas for our group to focus
Plants need good nutrition to grow well and avoid diseases,
adds Locke. And healthy plants need fewer chemicals, such as fungicides,
insecticides, or growth regulators. Were researching use of soilless
media as a way to further protect plants against disease and hold water
and nutrients for them. When youre growing plants in pots, you have
the opportunity to replace the soil entirely and eliminate possible soilborne
pathogensif you can fi nd a cost-effective way to do it.
Seeing Nutrient Needs, Molecularly
Locke and Frantz have made a lot of progress toward their goals in the
past 3 years. Frantz is testing commercial nutrient sensors as he tries
to design improved portable sensors. Devices like these can
give growers a few extra days to correct nutrition problems before their
plants are seriously damaged, he says.
To develop better portable sensors, he and colleagues are testing ways
to spot nutrition problems by identifying key proteins or other molecules
associated with stress. One of these ways is bouncing
infrared light off plants to analyze the molecules present. You
can see these proteins start working before you ever see any evidence
of damage in the stressed plant, Frantz says.
The GPRGs current research with silicon offers a window into how
the group operates with all the nutrients it studies, such as nitrogen,
phosphorus, potassium, and trace elements like magnesium. This
is true even thoughunlike those other nutrientsthe research
community doesnt yet agree on whether silicon is even an essential
plant nutrient. Frantz and Locke want to fi nd out whether it is essential
and, if so, just how much it can benefi t plants. To ascertain this, they
use various research tools such as hydroponic culturegrowing plants
in a nutrient-water solution.
For example, in a recent experiment with zinnias, the scientists delivered
silicon in irrigation water given to plants growing in potting mixes;
they added silicon to the hydroponic solution in which other plants were
growing. Then they exposed the seedlings to powdery mildew, a common disease
of greenhouse plants. The scientists examined leaf tissue using scanning
electron microscopy with energy dispersive spectrometry x-ray analyzers
at Wooster to determine silicon content and location. They assessed the
mildew visually and documented their observations with digital photography,
which was analyzed with special software to pinpoint the areas of powdery
After observing the zinnias daily for 4 to 6 weeks, the scientists then
harvested them and determined the fi nal total silicon content of leaf
tissue using inductively coupled plasma (ICP) spectrometry. With ICP,
plant tissue samples are burned in very hot plasma, which is created as
argon gas becomes electrically conductive after passing near a coil that
generates high-energy radio waves. The combustion creates a light spectrum
that makes it possible to identify elements including silicon, phosphorus,
potassium, copper, magnesium, and boron.
Frantz and Locke found that signifi cant amounts of silicon had accumulated
in the harvested zinnia leaves. The silicon also decreased the severity
of symptoms of powdery mildew infections in the zinnias. Next, the scientists
will use similar tests to see whether silicon accumulates in the leaves
of begonias, geraniums, and other ornamental crops.
We want to see which crops put nutrients where they are most useful
to the plant. It will help breeders choose promising lines for creating
new varieties of fl owers and ornamental plants that will need fewer pesticide
applications, Locke says.
How Do Nutrients Protect?
Locke says that he and colleagues have found that silicon helps to reduce
both insect and disease problems in geraniums and begonias as well as
in zinnias. In fact, an ARS postdoctoral researcher working with
these plants has found that silicon can reduce the incidence or severity
of the two most common foliar diseases of horticultural plantspowdery
mildew and Botrytis cinerea, Locke says. Now theyre using
these diseases as models to evaluate the role of mineral trace elements
on plant disease resistance.
Foliar fungal diseases of herbaceous bedding plants pose a serious
management challenge to greenhouse growers, says Krause. Disease
can spread rapidly in a greenhouse, where so many plants
are so close together. We want to fi nd out how nutrients protect plants
from diseases. For example, do they build protection in the cell walls,
or do they activate plant defense mechanisms?
Locke, working with Krause and OSU researchers, found that a potting mix
of composted hardwood bark, peat moss, and certain types of the benefi
cial fungus Trichoderma could combat Botrytis
gray mold on plant leaves. In begonias, it reduced this mold more
than the standard fungicide chlorothalonil did, Locke says.
But Locke and colleagues have found that more isnt necessarily better
with regard to applying nutrients. In tests on begonia and New Guinea
impatiens grown in sphagnum peat moss/perlite potting mixes, they applied
various rates of nitrogen and then infected the plants with gray mold.
They found that it doesnt pay to add more than 100 parts per million
of nitrogen. After that, you can green up the plants just before
sale, but you do so at the possible expense of more disease and poorer
overall plant growth and appearance, says Locke. In addition to
the University of Toledo and OSU, the ARS scientists work with colleagues
at North Carolina State University, the University of Florida, Michigan
State University, and the Cooperative Extension Services in Michigan,
North Carolina, and Ohio.
Were the new kid on the block, so we take advantage of the
years of expertise at the more established laboratories in those institutions,
Krause warns visitors that if you are at the Toledo Botanical Garden
and see government vehicles, individuals in white lab coats, or plants
growing with unusual equipment attached, you should think of it as the
plant equivalent of the University of Toledos medical college. To
do our research, we have many strangelooking sensors, gadgets, wires,
and computers connected to the potted plants so we can measure and record
everything from nutrient levels in their leaves to moisture in the soil
or potting media, says Krause. Weve deliberately inoculated
pathogens into some plants to help us study the various stress symptoms
resulting from nutrient defi ciencies, moisture conditions, and disease
We advise observers to think of this research area as an intensive
care unit for plantsone thats similar to hospital units where
patients are monitored with wires, tubes, and other devices to facilitate
recovery. Similarly, we need to carefully monitor the research plants
to obtain the information we need to develop better recommendations for
growing ornamentals more effi ciently and economically.
Toward Totally Automated Production
In one greenhouse, theres a small scale, called a lysimeter,
under each potted plant. The soil gets lighter as water moves through
and out of the plant. Some of the water applied to the plant is also
captured in the lysimeter box and sampled periodically for quality. The
researchers also test the quality of the water before its applied.
From these lysimeters, we gain an understanding of how much
water plants need so we can give them just the right amount and at the
right timing and pace, Locke says. We will eventually automate
watering based on the data we get from these lysimeter experiments.
Thanks to research findings to date, Frantz, Locke, and Krause have
published Virtual Grower software, which is available on the
World Wide Web. It can help growers manage their greenhouses
for greater productivity at lower costs. The current version focuses on
energy requirements, helping growers choose the best fuel and heating
schedules. It is available, free of charge, by going to www.
ars.usda.gov/services/software/software.htm and scrolling down to Virtual
Frantz and Locke will gradually expand the software to include all aspects
of greenhouse management, including applications of nutrients, water,
growth regulators, and pesticides. Ultimately, it will also
help growers to manage labor, optimize plant productivity, and set sale
prices. According to Frantz, There are many individual programs
like this, but none that considers all these factors interacting together
as this one will.
Editors Note: This research is part of Crop Production (#305)
and Plant Diseases (#303), two ARS National Research Programs described
on the World Wide Web at www.nps.ars.usda.gov.
James C. Locke and Jonathan M. Frantz are with the USDA-ARS Greenhouse
Production Research Group, 2801 W. Bancroft St., Mail Stop 604, Toledo,
OH 43606; phone (419) 530-1595 [Locke], (419) 530-1531 [Frantz], fax (419)
530-1599. Charles R. Krause is in the USDA-ARS Application Technology
Unit, 1680 Madison Ave., Wooster, OH 44691; phone (330) 347-6789, fax
© 2007 Columbia Publishing
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