5.2.4S
COMMERCIALIZATION OF SEED BACTERIZATION FOR BIOLOGICAL CONTROL OF SEEDLING AND ROOT DISEASES

PM BRANNEN

Gustafson Inc., Route 1, Box 339-A, McKinney, TX 75070, USA

Use of seed-applied, bacterial biocontrol agents (BCAs) for control of seedling and soilborne diseases has had limited utility throughout the world. Multiple attempts have been made to upscale production of viable cells, and most of these attempts have failed. When product forms have been successfully produced, even fewer products have made market penetration. There are several key technical reasons for the failures observed in commercialization of bacterial BCAs. Often, lab models have not closely mimicked those required for commercial-scale fermentation [1]. In addition, some biologicals are subject to genetic drift during development and fermentation; consistent production and quality assessment are required. If a product form can be developed, then it has to be easy to use and readily packaged. The BCA generally needs to remain stable in its container for 2 or more years. Since treated seed are often stored for more than 2 years, seed-applied BCAs should have a shelf life of a minimum of 2 years on the seed. Therefore, when combined with container stability, the ideal, seed-applied, bacterial BCA should be stable for a minimum of 4 years. Storage conditions are often adverse, with severe fluctuations of heat and humidity, so stability under adverse conditions also has to be tested.

Seed-applied BCAs should generally be utilized as a component of an integrated pest management system, to include chemical fungicides and insecticides. Stand-alone biologicals, though possible in some circumstances, are not the norm; most bacterial BCAs have very limited activity against seedborne pathogens, so chemical eradicants are generally required for this purpose. Since bacterial BCAs will be intimately associated with chemicals on the seed coat, BCAs must be compatible with standard seed-treatment fungicides and insecticides. In addition, since spermosphere and rhizosphere colonization are generally required for activity, the BCAs have to be compatible with soil-incorporated herbicides and insecticides. The BCAs have to integrate with current production practices.

Any of the above technical difficulties may stymie commercialization. However, failures have also resulted from not following basic principles used to promote all successful agricultural products -- sound field development and marketing. There has been an assumption by many that the use of biologicals will be driven by the need to replace chemical fungicides. However, markets will not generally yield to a BCA, even though safer, when it is less efficacious or more costly than current chemical standards. Ultimately, if a biocontrol agent is to be successful, it will be driven by the same market forces that drive any chemical.

KodiakŪ (Gustafson Inc., Plano, TX) is an excellent example of a successful, seed-applied, bacterial BCA [2]. Kodiak contains formulated endospores of Bacillus subtilis strain GB03, and Kodiak is readily produced with current fermentation and formulation technologies. Endospores are extremely stable, and they are compatible with most seed-treatment chemicals. With the advent of Kodiak, cotton (Gossypium spp.) has been the first large-scale, agronomic crop in the world treated with a BCA for suppression of seedling diseases and long-term chronic diseases of the rhizosphere. However, the wheat (Triticum spp.) and bean (Phaseolus spp.) markets are also being penetrated with this product. Field responses have typically been a mixture of growth promotion (increased root mass) and disease suppression (Rhizoctonia and Fusarium spp.). Strain GB03 has shown exceptional rhizosphere competence, and it has met all of the stated requirements for a successful BCA.

To summarize, in order to commercialize a bacterial, seed-treatment BCA, it must be efficacious and dependable, provide long-term storability in the package and on seed, be compatible with standard chemical fungicides and insecticides, be compatible with current production practices, and provide an economic return to the producer. Any deviation from these principles will result in failure.

References
1. Slininger PJ, Schisler DA, Bothast RJ, 1994. 3rd International Workshop on Plant Growth-Promoting Rhizobacteria, pp. 29-32.
2. Brannen PM, Kenney DS, 1997. Journal of Industrial Microbiology and Biotechnology 19, 169-171.