Influence of epidemiological factors on the bioherbicidal efficacy of a Xanthomonas capestris isolate on common cocklebur (Xanthium strumarium)

Authors: Boyette, Clyde; Hoagland, Robert

Submitted to: Journal of Experimental Biology and Agricultural Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2013
Publication Date: 9/20/2013
Publication URL: http://handle.nal.usda.gov/10113/60717
Citation: Boyette, C.D., Hoagland, R.E. 2013. Influence of epidemiological factors on the bioherbicidal efficacy of a Xanthomonas capestris isolate on common cocklebur (Xanthium strumarium). Journal of Experimental Biology and Agricultural Sciences. 1(4):209-216.

Interpretive Summary: The weed hemp sesbania, which is relatively tolerant to glyphosate, is a serious problem of soybean, rice, and cotton in the southern U.S., reducing quality and yield of these crops by as much as 40, 50, and 80%, respectively. The bioherbicidal fungus Colletotrichum truncatum can effectively control this weed if spores (conidia) are properly formulated. The objective of this project was to examine several adjuvants (surfactants and plant extracts) for possible augmentation of conidial germination and virulence of this organism, because components of bioherbicides should maintain or enhance conidial germination, growth, and infectivity on their target weeds. We found that some surfactants stimulated germination and virulence when formulated with conidia and applied to hemp sesbania leaves. Conidia formulated in water, a surfactant, or an emulsion of refined corn oil, were ineffective in the absence of dew or when dew was delayed. But, formulations of conidia plus surfactant in emulsified refined corn oil exhibited bioherbicidal activity when sufficient dew or free-moisture was available. This is important since previous reports indicated that refined corn oil did not enhance bioherbicidal activity, whereas unrefined corn oil promoted pathogen germination and efficacy. Aqueous extracts of several plant species also stimulated germination. This research is important since results show that formulations containing an emulsion of conidia, a surfactant and refined corn oil can improve C. truncatum efficacy, and suggest that similar formulations may also be applicable to other weed pathogens used as bioherbicides.

Technical Abstract: Greenhouse and controlled-environment studies were conducted to determine the effects of incubation temperature, dew period temperature and duration, plant growth stage, and cell concentration on the bioherbicidal efficacy of a highly virulent isolate (LVA987) of the bacterial pathogen, Xanthomonas campestris, as a bioherbicide against Xanthium strumarium (common cocklebur). X. campestris infected cocklebur at 20, 25, 30, and 35ºC but the disease achieved at 20ºC was not sufficient to cause high plant mortality. Plant mortality was also significantly lower in plants that were exposed to < 12 h of dew, or at dew temperatures of 15 or 35 ºC. Plants at the 0-4 leaf stage were controlled more efficaciously than older plants, and increasing cell concentration from 105 to 109 cells ml–1 resulted in higher mortality and biomass reduction levels. Results indicate that X. campestris can infect and kill cocklebur over a wide range of temperature, dew period, and inoculum levels and, therefore has potential as a bioherbicidal agent against common cocklebur.