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Optimizing the Efficacy of Beneficial Bacteria Against Botrytis Blight in Greenhouse Crops

Botrytis cinerea is the causal agent of botrytis blight or gray mold, the most common and economically devasting disease for greenhouse crops. Fungicides are routinely used to control Botrytis; however, some Botrytis strains are developing resistance to those chemicals. Beneficial bacteria have been used successfully as biological control agents for disease control. The Jones laboratory at Ohio State University has screened a collection of beneficial bacteria to identify strains that can control Botrytis blight in petunia. These experiments have identified some strains of Pseudomonas bacteria that are effective microbial biocontrol agents (MBCAs). We have characterized these bacteria to identify potential modes of action by which they inhibit the severity of Botrytis blight. This research was made possible by a research grant from the American Floral Endowment (AFE), and the complete reports can be found in part 1 and part 2.  Additional information can also be found in the research paper by South et al., 2020.

Additional resources for managing Botrytis blight can be found in AFE’s recently released Thrips and Botrytis Research Library. The library is free to all, thanks to the campaign’s generous industry sponsors, and designed to be a one-stop-shop, complete with informative webinars, insightful fact sheets, and engaging articles on the latest research and implementation strategy. It contains resources in both English and Spanish, as well as cutting-edge research reports that growers can implement into their business immediately.

METHODS

A consortium or community of bacteria may work better than a single bacteria strain to control diseases like Botrytis blight. Individual strains and combinations of strains were evaluated on detached flowers of Petunia ×hybrida ‘Carpet Red .’The flowers selected for this experiment were four days after flower opening because older flowers are more susceptible to Botrytis. The flowers were removed from the plant, and cut stems were put into a test tube filled with reverse osmosis (RO) water. Each flower was sprayed with a bacteria solution (Table 1 and 2).

After the bacteria solution dried on the detached flowers for two hours, the flowers were sprayed to run off with a solution of Botrytis spores. The flowers were closed inside Plexi-glass chambers, sealed with weather stripping to create a high-humidity environment, covered with cloth to decrease light, and kept at room temperature for optimal disease development. Each flower was rated for disease severity 48 hours after inoculation using a scale of 0 to 4 (Figure 1).

Figure 1

Figure 2. Control of Botrytis disease with single bacteria strains and combinations of strains. A. Visual symptoms of Botrytis blight on petunias with the various experimental bacteria treatments at 48 h after inoculation with Botrytis cinerea. B. Average disease severity ratings of flowers after treatment with single bacteria strains (solid bars), a mixture of two bacteria (dashed bars) or a mixture of three bacteria (cross-hatched bars). The asterisks or dots above the bars on the graph indicate that the treatment had significantly reduced disease severity compared to control flowers that were not treated with any bacteria. Cease is a commercial biofungicide that contains Bacillus subtilis.

RESULTS

Bacteria mixtures decreased Botrytis disease severity on petunia flowers. We found that 14B11, 15H3, AP54, 14B11+AP54, and 15H3+AP54 significantly decreased the disease severity caused by Botrytis (Figure 2). The combinations of 14B11+15H3 and 14B11+15H3+AP54 did not decrease disease severity. This aligns well with results found in our bacterial characterizations, which indicate that 15H3 has negative effects on the growth and function of 14B11 and should not be used together in a combined treatment. 

Combining bacteria strains together can be a powerful tool in creating an MBCA with efficacy in a diverse variety of floriculture crops. We have identified key lab assays that should be conducted to evaluate bacteria so that informed decisions can be made on what bacteria to include in a consortium for future product formulation. Through these lab assays and plant trials, we identified bacteria consortia that act as an MBCA for Botrytis,control in petunia and individual strains that are also highly efficient on their own for reducing the severity of the disease.

By Michelle Jones, Laura Chapin, and Sachin Naik, Dept. Horticulture and Crop Science, The Ohio State University, Wooster, OH