Q-318. Field Plot Studies of Survival and Growth of the Biocontrol Agent Bacillus Strain 1BA Applied To Wheat Heads

B. H. Bleakley, J. Morgan;
South Dakota State Univ., Brookings, SD.

Fusarium graminearum causes Fusarium Head Blight on wheat. Biocontrol agents (BCAs), such as certain Bacillus sp., sprayed onto the wheat heads at or near anthesis can be used to control FHB. Populations of Bacillus strain 1BA, a salt-tolerant and thermotolerant BCA, were studied during 2006 and 2007 in field plots. We hypothesized that numbers of Bacillus 1BA would fluctuate over time; that different growth media (complex versus defined) used to grow the BCA would result in differences in its survival; and that addition of fungicides and/or spreaders/stickers to the spray mix would result in differences in numbers of 1BA. Field plot treatments in 2006 used cells of 1BA grown in several different broth media; and including the fungicide Folicur with a spreader or sticker in some treatments. Field plot treatments in 2007 were 1BA by itself; and 1BA + Prosaro (a fungicide mix) + Induce NIS (nonionic surfactant). Population counts were done over a 20 day period via MPN technique. Controls not receiving 1BA inoculation gave low cell counts in both years, no higher than about 3.5 X 102 CFU/g fresh plant weight. In both years, there was a rapid decline in numbers of 1BA on grain heads in the first few days after spraying, followed by an increase in numbers in some treatments to levels around 104 CFU/g fresh plant weight. Treatments using 1BA grown in defined broth yielded lower numbers of 1BA on wheat heads over time than treatments using 1BA grown in complex broth. In both years, some treatments showed a major increase in 1BA numbers around 10 days after spraying. In 2007 in the treatment with 1BA alone, vegetative cell counts peaked around day 10, then declined sharply, followed by a second increase in numbers by day 20, with an increase in endospore numbers. Compared to the treatment with 1BA alone, in the treatment combining 1BA with Prosaro and Induce NIS, population peaks shifted in time. Peak numbers of vegetative cells occurred at about day 6 then declined. As vegetative numbers of 1BA in this treatment declined, endospore numbers increased. Survival and growth of the BCA on wheat heads is greatly affected by the medium used to grow BCA inoculum, and by fungicides and adjuvants in spray mixtures.

251/Q. Microbiology of Wastes and Waste Treatment - II

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