William J. Connick

Formulation Of Microorganisms To Control Plant Diseases

Formulations affect many aspects of the success of biocontrol organisms, including the shelf-life of a product, ability of a biocontrol organism to proliferate and survive in the environment, effectiveness for disease control, ease of preparation and application, and expense. Recent review articles have discussed these topics as well as production of biocontrol organisms (Lumsden and Lewis, 1989; Connick et al., 1990; Fravel and Lewis, 1992; Harris, 1994; Lumsden et al., 1995). This chapter discusses formulation of commercially available biocontrol organisms for control of plant pathogens and research on the development of these organisms.

Seed-germination inhibition by volatile alcohols and other compounds associated withAmaranthus palmeri residues.

Effects of 3-pentanone and eight low molecular weight aliphatic alcohols and aldehydes identifed in the mixtures of volatiles released byAmaranthus palmeri S. Wats. (AMAPA) residues were determined on germination of onion, carrot, AMAPA, and tomato seeds. Three-day exposures to these volatiles significantly inhibited germination of these assay seeds, and the inhibition was dependent upon exposure time and concentration. Based on the degree of inhibition observed in both time- and concentration-dependent assays, the following activity series was obtained: 2-heptanol > 3-methyl-1-butanol, 1-hexanol > hexanal, 1-pentanol, 3-pentanone, acetaldehyde > ethanol, 2-methyl-1-propanol. The activities of this group of compounds with that of 2-heptanone appear to be additive and related to test compound volatility and hydrophilicity. 2-Heptanol and 2-heptanone also significantly inhibited the germination of other species, including shepherdspurse, soybean, lettuce, alfalfa, common purslane, oats, and lovegrass.

Stability of microsclerotial inoculum of Colletotrichum truncatum encapsulated in wheat flour-kaolin granules.

Maintaining adequate viability of microorganisms in products for biocontrol is critically important for commercial reasons. Microsclerotia (MS) of the mycoherbicide agent, Colletotrichum truncatum, are its hardy, over-wintering fungal structures. Microsclerotial inoculum at 2, 7, and 23 MS/granule were matrix-encapsulated in wheat flour–kaolin granules (‘Pesta’), in which the flour provided gluten for the matrix and a food base for the fungus. Pesta granules were dried to a water activity of 0.18–0.29. After storage for 52 weeks at 25°C, granules containing 7 and 23 MS were 100% viable and granules with 2 MS were 95% viable. Granules with 7 MS were 50% viable after 36 weeks at 35°C. Pesta granules (440 granules/g) with conidial inoculum at 3.3×105 c.f.u./g were less storage-stable than granules at the 2 MS/granule level. At all MS inoculum levels, granules stored for up to 2years produced 108 c.f.u./g in vitro when incubated on water agar. High water activity was detrimental to long-term viability. In the greenhouse, 7 MS/granule samples controlled 94% of hemp sesbania when incorporated into the soil pre-planting. The strategy of encapsulation of the naturally stable C. truncatum MS and drying to a favourable water activity led to excellent shelf-life for a live biocontrol agent.

Solid-state fermentation plus extrusion to make biopesticide granules

Five fungal biocontrol agents useful in agriculture were grown on rice flour in plastic bags. The flour, infested with Colletotrichum truncatum, an Alternaria sp., Paecilomyces fumosoroseus, or atoxigenic Aspergillus flavus and A. parasiticus, was mixed with wheat flour, kaolin, and water and extruded into granules. The inoculum survived extrusion and fluid bed drying at 50°C 3–92 times better than inoculum produced in liquid fermentation. Depending on the agent, the high level of flour infestation permitted a 1:9 to 1:1600 dilution to yield the 1×106 cfu/g in the final product which is usually needed for biocontrol efficacy.

Volatile methyl ketone seed-germination inhibitors fromAmaranthus palmeri S. Wats. Residues.

The effects of nine methyl ketones previously identified in the mixture of volatiles released byAmaranthus palmeri (AMAPA) residues upon onion, carrot, AMAPA, and tomato seed germination were determined. Three-day exposures to these volatiles significantly inhibited germination of all assay seeds, and the degree of inhibition was dependent upon seed species, exposure time, and concentration. Based on the degree of inhibition observed in both time- and concentration-dependent assays, the following activity series was obtained: 2-octanone, 2-nonanone > 2-undecanone > 2-heptanone > 2-hexanone, 3-methyl-2-butanone, 2-pentanone, 3-hydroxy-2-butanone > 2-butanone. The activities of these compounds appear to be additive and dependent on relative volatility and hydrophilicity.

Formulation of filamentous fungi for bioremediation

Mycelia of Marasmiellus troyanus embedded in calcium alginate granules with corn cob grits as a nutritive amendment were viable after one year with refrigeration but inviable when stored at room temperature. With refrigeration, Phanerochaete chrysosporium mycelia and spores embedded in alginate were both viable after one year. At room temperature, spores encapsulated in alginate granules gave good viability while mycelial formulations did not. In all trials, corn cob grits was superior to saw dust for extending shelf life. Corn cob grits-amended granules of both species were able to germinate and grow in both uncontaminated soil and chemical waste-contaminated soil.