Features Production Research
Grafting can help fight foliar diseases

June 2, 2010, Wooster,
OH – It’s not uncommon to use grafting to strengthen resistance against
soil-borne diseases. But Ohio State University researchers have discovered that
the method can also fight off foliar diseases.

June 2, 2010, Wooster,
OH – It’s not uncommon to use grafting to strengthen resistance against
soil-borne diseases. But Ohio State University researchers have discovered that
the method can also fight off foliar diseases.

Brian
McSpadden-Gardener, a microbial ecologist with the Ohio Agricultural Research
and Development Center, found that grafted tomato plants appear to be more
resistant to foliar diseases than ungrafted tomato plants of the same genotype.
McSpadden-Gardener’s work is part of a larger, three-year, multi-state project
that is exploring the use of grafting to improve tomato production,
specifically in high tunnels and organic production.

“We chose tomato because
it is susceptible to a number of field stresses, is very important
economically, and responds to grafting,” said Matt Kleinhenz, an Ohio State
University Extension vegetable crops specialist.

OARDC researchers
involved in the project include Kleinhenz, McSpadden-Gardener, geneticist David
Francis, and plant pathologist Sally Miller. The group genetically bred 46
rootstocks and grafted them to the tops of two popular tomato cultivars:
Cherokee Purple and Celebrity. They then compared field and high tunnel grafted
tomatoes to non-grafted tomatoes and found that in both production systems,
grafted tomatoes out-yielded non-grafted tomatoes anywhere from five per cent
to 30 per cent.

The yield increases were
greatest in the presence of soil-borne diseases and in drought conditions.

“Grafting plants is done
primarily to protect them from soil-borne diseases by using vigorous rootstocks
and scions from often less hardy, but more flavorful varieties,” said
McSpadden-Gardener. “Because root microbiology is known to be affected by
cultivars and such differences can affect the plant’s immune system, we were
interested in studying the relationships between grafting and disease
resistance. In last year’s field study, we observed that grafted plants tended
to be less severely affected by foliar diseases than ungrafted plants, which
supports our hypothesis that root-microbe interactions can affect the scion.”

Grafting-induced disease
reductions were observed for Septoria leaf spot and late blight. However,
because of the relatively small scale of the study, it is not clear how
significant those reductions might be in economic terms.

In addition, when
researchers examined the biochemistry of the grafted tomato leaves they found
increased levels of two flavonoids. Flavonoids are antioxidants found naturally
in plants that serve a wide variety of functions including giving flowers their
color and protecting plants from insects.

McSpaddener-Gardener
said that one of the flavonoids has been identified as alpha tomatine and is a
component of the plant’s immune system.

“The second flavonoid
has yet to be identified but appears to be even more responsive to grafting,”
said McSpadden-Gardener. “What was even more surprising was that the
differences were observed over eight weeks after the initial grafting event, an
indication that grafting has long-lived effects on host physiology prior to
fruiting.”

Through fruit and
vegetable consumption, flavonoids are known to be beneficial to the human body
by triggering the production of natural enzymes that help fight off diseases
such as cancer, heart disease and age-related degenerative illnesses.

“At this time, it is not
clear if the observed changes in flavonoid content in the foliage also occur in
the edible fruit,” said McSpadden-Gardener. “Future work will need to be done
to characterize the types of biochemical changes that occur in both the fruit
and foliage in order to determine if such responses have impacts on fruit
quality. But this is a good starting point.”

OARDC researchers are
collaborating with researchers from the University of Minnesota, West Virginia
State University, North Carolina State University and Penn State. Farmers have
also contributed significantly to the project from the beginning and continue
to test the performance of grafted plants on their farms.

“Most farmers have a
favorite tomato variety and heavily rely on just a few varieties that produce
fruit the market wants,” said Kleinhenz. “Consumers are looking for specific
characteristics – weight, size, colour, taste, how well it keeps, etc. Grafting
means a greater ability for farmers to provide these qualities under
challenging field conditions while maintaining ties to sustainability for
consumers.”

Future work will help
determine the range of diseases impacted by grafting and the magnitude of the
disease reductions in biological and economic terms.

For more information on
grafting, log on to http://oardc.osu.edu/graftingtomato/graft.htm.