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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVEMENT OF BIOHERBICIDE STRATEGIES FOR INVASIVE WEEDS IN SOUTHERN CROPPING SYSTEMS

Location: Biological Control of Pests Research Unit

Title: Interactions of Chemical Additives, pH, and Temperature on Conidia Germination and Virulence of Colletotrichum truncatum, a Bioherbicide of Sesbania exaltata

Authors
item Boyette, Clyde
item Hoagland, Robert

Submitted to: Allelopathy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 22, 2012
Publication Date: July 1, 2012
Citation: Boyette, C.D., and Hoagland, R.E. 2012. Interactions of chemical additives, pH, and temperature on Conidia germination and virulence of Colletotrichum truncatum, a bioherbicide of Sesbania exaltata. Allelopathy Journal. 30:103-116.

Interpretive Summary: Conidia (infective units) of a biological weed control fungus (bioherbicide) can be used to control hemp sesbania, an economically important weed in rice and soybeans. In order to be an effective bioherbicide, conidia must be able to germinate over a wide range of conditions. We found that conidia germinated over a wide pH range. Rinsing conidia with water improved germination. Low temperatures increased germination and infection compared to high temperatures. Germination was not affected by exposure to light or dark conditions. Low concentrations of some amino acids, sugars, and plant extracts (hemp sesbania and pigweed) stimulated germination and infectivity of hemp sesbania, but one amino acid was strongly inhibitory. Results from this research revealed that some factors which stimulate conidial germination of this fungus also enhance pathogenicity against hemp sesbania. Manipulation of these factors may improve the potential of this fungus as a bioherbicide.

Technical Abstract: We studied several factors that influence conidial germination and pathogenicity of the fungus Colletotrichum truncatum, which is a potential bioherbicide for hemp sesbania. The conidia germinated on 2% water agar over the pH range of 3.5 to 9.0, and the optimal pH for germination depended upon the specific buffer used. Citrate and acetate buffers of low pH inhibited germination. Percent germination decreased as buffer concentrations increased from 1 to 100 mM and as conidial density increased. Washing the conidia improved germination percentage. Temperatures of 15º and 20ºC were more favorable for germination and infection of hemp sesbania than 35º and 40ºC, but emergence of germ tubes from each cell of the two-celled conidia and growth and branching of germ tubes were greater at 35º than at lower temperatures. Increased germination and branching from both conidial cells did not result in increased infectivity. Percent germination was nearly equal under light or dark conditions. Additions of 10 mM amino acids (alanine, glycine, phenylalanine, tryptophan), 10 mM sugars (glucose, galactose, xylose) and extracts of various plants, such as hemp sesbania and pigweed stimulated germination, but cystine strongly inhibited germination. Only alanine or xylose enhanced infectivity when applied with the conidia to hemp sesbania seedling tissues.

Last Modified: 7/24/2014
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