Controlling Bakanae Disease-03



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Project Leader and Principal UC Investigators

Allen Van Deynze, biotechnology specialist, Seed Biotechnology Center, UC Davis


The goal of this project is to evaluate ozone for control of Bakanae, a seed-borne disease that erupted in California during 1999. Preliminary data from laboratory tests indicate that ozone may be a safe and effective seed treatment to control this fungus.

Ozone is a pungent, unstable, bluish gas that readily breaks down organic molecules. It is routinely used as a disinfectant in the food industry to control bacterial or fungal growth for fresh fruits and vegetables. It readily breaks down into nothing more than oxygen and is ubiquitous in the environment. It has no safety issues at the exposure levels being tested or proposed for this application. Food safety experts have granted it wide acceptance in the United States. This study thus sought to tests ozone's performance against Bakanae Disease in the laboratory and in field locations and then to design a treatment method for applying ozone during aerial seeding.

Ozone had previously proven effective controlling Bakanae fungal spores on presoaked seeds but not on dry seeds. Under dry conditions, spores are dormant and resistant to biocides. Presoaked seeds, on the other hand, place the fungus in a more active and vulnerable state. UC Davis researchers examined the moisture content of presoaked seed in soaking bins and trucks prior to seeding. After a 20-24 hour soaking, rice seed showed little variation in moisture. It ranged between 16 percent and 22 percent, most of that variation occurring within a trailer as opposed to over time.

A laboratory experiment tested three different doses of ozone at three times on presoaked seeds in an effort to narrow the number of treatments necessary for field trials. All treatments showed a significant reduction in Bakanae spores relative to the control group, regardless of dose or length of time. Based on these results, researchers then turned their attention to field experiments, where ozone was again tested at three levels on seed with 20 percent moisture to simulate conditions just prior to seeding. Seed was planted within 24 hours of treatment and data was taken on stand, seedling vigor, number of Bakanae seedlings per square foot, number of dead heads, tillers per square foot and yield.

Unfortunately, as far as this experiment was concerned, 2003 proved to be a poor year for Bakanae Disease in California. Consequently, only limited conclusions can be drawn from last year's work. All ozone treatments showed a significant decrease in Bakanae relative to untreated controls. Numerically, ozone treatments were not as efficacious as bleach treatments at all sites. Further evaluations are necessary to determine whether ozone can be effective for Bakanae control in the field.

The third objective was to design a treatment for applying ozone in the field during aerial seeding. Work began on retrofitting a four-by-four foot seed bin with a lid and manifolds to deliver ozone through presoaked seed and measure the ozone concentration at various locations within the bin. Initial financial calculations included the capital cost of an ozone generator and operating costs amortized over seven years. This worked out to $1/acre based on a 200 pound per acre seeding rate. The cost drops to 20 cents per acre after the ozone generator is paid off. Generator costs ranged between $70,000 and $98,000.

The cost of using bleach to control Bakanae Disease is significantly less and may prove to be the most cost-effective alternative. Further evaluations are necessary to determine whether ozone can be an effective treatment in the field but its costs are significantly greater than a bleach alternative, as long as there are no disposal costs associated with bleach-treated water.


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