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United States Department of Agriculture

Agricultural Research Service

Title: Twin Screw Extrusion of Pesta-Encapsulated Biocontrol Agents

Authors
item Daigle, Donald
item Connick Jr, William
item Boyette, Clyde
item Lovisa, Mary - DELTA STATE UNIVERSITY
item Williams, Kelley
item Watson, Michael

Submitted to: Journal of Microbiology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 10, 1997
Publication Date: N/A

Interpretive Summary: The problems of preparing pound quantities (semi-pilot plant) of granules containing biocontrol agents by twin-screw extrusion was studied. Water concentration was found to be critical especially with Colletotrichum truncatum, a pathogen of hemp sesbania. Hemp sesbania is a troublesome weed in soybeans, particularly in the lower Mississippi Valley. It is also a problem in rice and cotton. The granules containing C. Truncatum did incite disease but methods to reduce the loss of inoculum in preparation of the granules must be found. Loss of inoculum was not as great with Alternaria conjuncta, a pathogen of swamp dodder. Swam dodder is found in cranberry bogs. There was no loss of inoculum with atoxigenic Aspergillus spp. These strains of Aspergillus are used in biocompetition to reduce levels of aflatoxin in food crops which include peanuts and corn. Aflatoxins are known carcinogens and responsible for making the commodity unfit for consumption.

Technical Abstract: "Pesta" granules in which fungal propagules are encapsulated in a wheat gluten matrix were prepared in multi-pound quantities by twin-screw extrusion and dried in a fluid bed dryer. The colony forming units (c.f.u.)g to minus one of these granules were compared to the c.f.u. g to minus one of samples prepared in gram quantities with a small pasta maker and air dried, ground, and sieved. In the dough formulation of wheat flour, clay filler, fungus and water, low water concentration (26%) reduced the viability of Colletotrichum truncatum, a pathogen of hemp sesbania (Sesbania exaltata (Rydb.) ex. A.W. Hill) by 90%. This loss of viability was moderate with Alternaria conjuncta/infectoria (55%), a pathogen of swamp dodder (Cuscuta gronovii, Willd.), and non-detectable with atoxigenic strains of Aspergillus flavus and Aspergillus parasiticus, used in biocompetetive studies. Drying the granular product to approximately 7% moisture content further reduced the viability of Colletotrichum truncatum (98%), Alternaria conjuncta/infectoria (65%) and Aspergillus parasiticus (93%). In the greenhouse, twin-screw-extruded (1.5 mm dia. X 2 mm) granules containing C. Truncatum (5 x 10 to the fourth c.f.u. g to minus one) caused high levels of infection and mortality in the target weed, hemp sesbania.

Last Modified: 4/24/2014
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