Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 14, 1995
Publication Date: N/A
Interpretive Summary: Take-all is the most significant root disease of wheat world-wide. Varieties resistant to root diseases are not available, and cultural control practices are not economically feasible. Chemical methods of control face a number of barriers including prohibitive expense, unreliability in certain regions and public concern over environmental safety. Biological control methods using bacteria, which have been implicated in the natural biological control known as take-all decline, have great potential as an alternative method of disease control. A particular bacterium (Pseudomonas fluorescens strain 2-79, NRRL B-15132) produces an antibiotic which acts as the primary mechanism of disease suppression. However, the lack of liquid culture technology needed for mass producing inexpensive and storable formulations of this bacterium has been an impediment to its commercialization. The research reported herein describes the impact of liquid growth culture, cell age, metabolites and formulation on the storage survival, seed compatibility and efficacy of the biocontrol agent product. These results will be used to optimize mass production and formulation of this bacterium with maximum capacity for storage and disease control.
Technical Abstract: Strain 2-79 is a biocontrol agent against take-all, a detrimental root disease of wheat caused by Gaeumannomyces graminis var. tritici. In the rhizosphere, it produces the antibiotic phenazine-1-carboxylic acid (PCA) as the primary means of disease suppression. Barriers to the commercial use of phenazine-producing pseudomonads, such as strain 2-79, include lack of liquid-culture and formulation technologies needed to optimize cost-effective mass production and application. There is little published research concerning the impact of growth culture physiological state and associated metabolites on resultant biocontrol agent efficacy, phytotoxicity and storage survival. To explore these issues, cells of strain 2-79 in various physiological states were obtained by harvesting fermentors at 24-h time intervals after inoculation. Cells formulated in 0.5% methylcellulose (M) suspended in either water (W) or metabolite-bearing, spent culture broth (SB) were applied as wheat seed coatings, air dried and stored at 4 deg C. Younger cells had twice the drying survival rate but half of the storage life of older cells. Cell populations surviving drying were 3.5 times higher in MW than in MSB formulations and remained viable ~3 times longer. This formulation effect on viability was due to culture nutrients but not metabolites present. Disease suppression in bacterized seed treatments did not vary with culture age, encapsulation media or storage time. Seedling height increased with disease suppression and decreased with lengthening storage time. Seed batches inoculated with cells in both MW and MSB encapsulations suffered germination losses due to phytotoxic metabolites. The rate of loss per 6 months' storage of MSB- and MW-coated seeds was 54 and 11%, respectively.