Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2004
Publication Date: 6/4/2005
Citation: Leland, J.E., Mullins, D.E., Vaughan, L.J., Warren, H.L. 2005. Effects of media composition on metarhizium anisopliae var. acridum spores, part 1: comparison of cell wall characteristics and drying stability among three spore types. Biocontrol Science and Technology.
Interpretive Summary: A fungus that kills insects produces three different spore types. Two of the spore types can be grown in liquid culture and the third in solid culture. Growing the spores in liquid culture may be more economical, but the spores may not have characteristics suitable for storage and use in insect control. The structure of these spore types and the properties of their outer surfaces were compared. This information will help describe the spore types and relate to their ability to control insect pests. Performance characteristics, such as how fast the spores germinate and how well they survive drying, were also studied. This study shows that one of the spore types produced in liquid culture has two positive attributes, it kills insect well and survives drying. This may have practical applications for improving the economics of production, producing a spore form that can survive drying, and improving insect control.
Technical Abstract: Metarhizium anisopliae var. acridum (IMI 330189) can produce at least three spore types in vitro; blastospores, submerged conidia, and aerial conidia, as defined by culturing conditions, sporogenesis, and spore morphology. This study compares morphological characteristics (i.e. spore dimensions and cell wall cross sections), chemical properties of cell wall surfaces (i.e. hydrophobic microsites, surface charge, and lectin binding), and performance (i.e. germination rate and drying stability) among these three spore types. Submerged conidia and aerial conidia both possessed thick, double-layered cell walls, with hydrophobic regions on their surfaces. However, submerged conidia can be differentiated from aerial conidia by: 1) their greater affinity for the lectin concanavalin-A; 2) more anionic net surface charge; and 3) less distinct outer rodlet layer. Blastospores were longer and more variable in length than both submerged conidia and aerial conidia, and had thinner single-layered cell walls that lacked an outer rodlet layer. Also, blastospores had a greater affinity than either conidia type for the lectin, wheat germ agglutinin. They lacked hydrophobic regions on their surface, and had a less anionic net surface charge than submerged conidia. In culture blastospores germinated the fastest followed by submerged conidia, and then aerial conidia. Survival of submerged conidia and aerial conidia were similar after drying on silica gel, and was greater than that for blastospores. We provide corroborating information for spore type names previously based on method of production, sporogenesis, and appearance of spores. These physical characteristics may have practical application for predicting spore-performance characteristics relevant to production and efficacy of mycoinsecticides