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Current Projects

(1) Development and application of molecular assays for characterizing the diversity and distribution of plant-associated microbes. Billions of diverse microbes colonize plant surfaces; however little is known about the ecological interactions among these organisms and how they might impact plant health. We have accumulated a collection of root and soil DNA from farms spread all across Ohio. This collection will provide the basis for long-term studies on the distribution and abundance of diverse microbial populations in agricultural fields. In order to characterize the microbial communities present in these samples, we have applied molecular profiling, specifically T-RFLP-based analyses, to identify and recover novel microbial populations that are quantitatively associated with soilborne disease suppression. Such an approach has the potential to revolutionize how new biopesticidal strains are discovered. Once recovered, strain- and species-specific markers can be used to further study their distribution and activities in the environment. For example, our laboratory's studies of biocontrol strains of Bacillus subtils has yielded a number of genetic markers for biocontrol functions in this diverse species.

Related References: 2001a, 2006, 2007a, 2009a

(2) Integrated research examining the effects of farm management practices on diverse plant-associated microbes. The environmental effects of agricultural practices on diverse, plant-associated microbial populations. We are examining the impact of different field management practices on soil and rhizosphere microbial communities and their activities in different production systems. This work initially developed through collaborations involved in the OARDC’s Organic Food, Farming, Education and Research (OFFER) program and has largely focused on tomatoes and other vegetable crops in periurban systems. However, recent work also examined impact of agronomic practices on biocontrol bacteria in corn and soybeans. To date, we have concluded three projects examining changes in soil and rhizosphere microflora associated with a) transition to organic vegetable production and b) typical management of corn and soybeans. We have found that several farm practices can significantly impact crop health in season and across seasons. Indeed, soilborne disease suppressiveness can be promoted by certain cropping strategies and the biological basis for such changes is the focus of ongoing investigations. We were the first to show that increases in certain native bacterial populations following a certain cropping strategywere positively-associated with elevated levels of disease suppressiveness and/or improved crop health. Such studies point the way to new integrated approaches for plant disease control.

Related References: 2007b, 2008a, 2008b

(3) Determining the contributions of biocontrol bacteria to crop health: Basic studies and applications for improved crop productivity. Antibiotic-producing pseudomonads represent a class of bacteria with great potential for development as biological controls of plant diseases. We have described the agricultural biogeography, ecology, and biocontrol efficacy of pseudomonads that produce the antibiotic 2,4-diacetylphloroglucinol (DAPG). Specifically, we determined the abundance and diversity of DAPG-producers that colonize the roots of corn and soybeans grown on conventional and organic farms located throughout Ohio. Recent work has focused on understanding the diverse mechanisms by which DAPG producers benefit plants. We recently showed that DAPG can alter plant root morphology, indicating that this well known antibiotic can also act directly to alter the structure of the host. We also found that at least some strains of DAPG-producers can alter nutrient uptake in plants. Specifically, we noted that strain Wood1R could reduce acid soil stress. Such work further indicates the complex interactions that a single bacterial population can have with its host.

In the field, we established that the abundance of native populations was positively correlated with stands and yields in corn. This work proved that biocontrol bacteria act in a dose-dependent manner in much the same way as had been shown for inoculated fields. In order to make use of the activities of these bacteria, we have tested the potential for DAPG-producing Pseudomonas spp. to improve crops stand and yield at multiple locations and shown their utility as a seed treatment. In those studies we also determined the feasibility of different inoculation procedures to maximize viability of the inoculum and, thus, provide greater flexibility to farmers for planting. Our novel formulation allows for convenient seed treatment at a cost of pennies to the acre. And, before biopesticides will be widely adopted, the government regulators will need to be satisfied that no undue risk can be associated with their application. Using T-RFLP we showed that disturbances in bacterial community structure following biopesticide application tend to be of small magnitude and of short duration under controlled conditions (i.e. in a growth chamber). Thus, it seems likely that biocontrol seed treatments will prove to be both effective and environmentally-friendly means of controlling soilborne root diseases of various crops.

Related References: 2001a, 2001b, 2004, 2005, 2007b, 2009b