Wooster, Ohio
June 9, 2009
Common plant-associated bacteria,
best known to suppress soil-borne root diseases, now have been
found to boost corn yields in low-pH soils. The discovery made
by Ohio State University plant
pathologists is the first-known documentation of a
root-colonizing bacterium improving plant health in acidic soil
conditions.
"No one in the past has identified such microorganisms as having
such a profound effect on protecting the plant under situations
caused by low soil pH," said Brian McSpadden Gardener, an Ohio
State University plant pathologist with the Ohio Agricultural
Research and Development Center and principal investigator of
the project. "The discovery could pave the way for more
sustainable cropping practices based on microbial inoculants.
This includes organic farmers who cannot use chemical seed
treatments, as well as those farmers in developing countries who
don’t have access to affordable lime to manage soil acidity that
often can limit crop yields."
The study, "Seed Treatment with
2,4-Diacetylphloroglucinol-Producting Pseudomonads Improves Crop
Health in Low-pH Soils by Altering Patterns of Nutrient Uptake,"
was recently published in the journal Phytopathology.
During a study to test the efficacy of DAPG-bacteria for disease
control, McSpadden Gardener and his colleagues were surprised to
find remarkable differences in plant growth in a portion of the
field, which was later found to be more acidic than the rest of
the field. Follow-up work showed that the bacterial seed
treatment prevented the development of abiotic stress disorder
and increased yields of corn plants growing in acidic soils
(i.e., with pH levels less than 5.0).
In two consecutive growing seasons, the researchers found that
corn plants treated with DAPG-producing bacteria were taking up
more essential nutrients, such as phosphorus, potassium, calcium
and magnesium, while limiting the amount of aluminum and
manganese, which can be toxic in high levels.
"In low-pH soils, most crops experience nutrient stress in the
form of phosphorus deficiencies and aluminum and/or manganese
toxicity. The plants show loss of chlorophyll with specking and
streaking of plant leaves," said McSpadden Gardener. "Seed
treated with DAPG-producing bacteria relieved that stress and
the plants grew normally."
The bacteria used in the experiments represent a widely
distributed Pseudomonas fluorescens strain that produces a
biofungicidal compound called 2,4-diacetylphloroglucinol (DAPG).
This compound is known to help suppress soil-borne diseases and
stimulate the plant's immune system. However, it is not clear
whether DAPG or some other products produced by the tested
strain are responsible for the newly discovered beneficial
effects under acidic soil conditions.
How DAPG-producing bacteria are altering plant uptake is not yet
known, but the researchers speculate that either the bacteria
are altering the plant's physiology to allow uptake of needed
nutrients while preventing the uptake of more toxic ones, or
alkalizing the soil around the plant's root zone so that the
plant is not exposed to low ph-soils around it.
DAPG-producing bacteria, with all of their myriad plant health
benefits, are not yet commercially available in the United
States. But McSpadden Gardener's research, as well as studies
conducted elsewhere, have indicated that these bacteria can
provide viable options for low-cost, natural crop protection.
The research was funded, in part, by a USDA National Research
Initiative grant and an OARDC Integrated Pest Management program
grant. |
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