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," says Brian McSpadden Gardener, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center (OARDC) 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," he explains.
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," says 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.