Bioherbicidal potential of Xanthomonas campestris for controlling Conyza canadensis

Authors: Boyette, Clyde; Hoagland, Robert

Submitted to: Biocontrol Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2014
Publication Date: 11/4/2014
Publication URL: http://handle.nal.usda.gov/10113/60795
Citation: Boyette, C.D., Hoagland, R.E. 2014. Bioherbicidal potential of Xanthomonas campestris for controlling Conyza canadensis. Biocontrol Science and Technology. 25:229-237.

Interpretive Summary: Horseweed (Conyza canadensis), native to and widespread in North America, is problematic in cotton, grain sorghum, corn and soybean. Various horseweed biotypes have developed resistance to several herbicides, including glyphosate. Greenhouse and controlled-environment studies were conducted to determine the effects of incubation temperature, dew period temperature and duration, plant growth stage, and inoculum concentration on the bioherbicidal efficacy of a virulent isolate of the bacterial pathogen, Xanthomonas campestris, as a bioherbicide against glyphosate-resistant and –susceptible horseweed. X. campestris infected both glyphosate-resistant and -susceptible C. canadensis plants at various growth stages when incubated at 20, 25, 30, and 35ºC, with a 20 hr dew period following inoculation, but at 20 and 40ºC disease severity was not sufficient to cause high plant mortality. Plant mortality was also significantly lower when plants were subjected to < 12 hr of dew, or at dew temperatures of 15 or 35 ºC. Plants in the rosette leaf stage of growth were controlled more efficaciously than older plants that had bolted, and increasing cell concentration from 105 to 109 cells/ml resulted in significantly greater plant mortality and biomass reduction. Results indicate that X. campestris can infect and kill C. canadensis over a wide range of temperature, dew period, and inoculum levels, thus demonstrating that this pathogen has potential as a bioherbicidal agent against this troublesome weed.

Technical Abstract: Greenhouse and controlled-environment studies were conducted to determine the effects of incubation temperature, dew period temperature, dew period duration, plant growth stage, and inoculum concentration on the bioherbicidal efficacy of a highly virulent isolate (LVA987) of the bacterial pathogen, Xanthomonas campestris, against glyphosate-resistant and –susceptible Conyza canadensis (horseweed). X. campestris infected this weed at various growth stages during incubation at 20, 25, 30, and 35ºC following a 20 hr dew period after inoculation although at 20ºC disease severity was not sufficient to cause high plant mortality. Plant mortality was also significantly low when plants were subjected to < 12 hr of dew, or at dew temperatures of 15 or 35 ºC. Plants in the rosette leaf stage of growth were controlled more efficaciously than older plants that had bolted. Increasing cell concentration from 105 to 109 cells/mL resulted in higher plant mortality and biomass reduction. Results indicate that X. campestris can infect and kill C. canadensis over a wide range of temperature, dew period, and inoculum levels, thus demonstrating its potential as a bioherbicidal agent against this weed.