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Title: Effects of elevated co2 on biomass and fungi associated with two ecotypes of ragweed (Ambrosia artemisiifolia L.)

Author
item Runion, George
item Prior, Stephen - Steve
item Price, Andrew
item MCELROY, S - Auburn University
item Torbert, Henry - Allen

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2014
Publication Date: 9/26/2014
Citation: Runion, G.B., Prior, S.A., Price, A.J., Mcelroy, S., Torbert III, H.A. 2014. Effects of elevated CO2 on biomass and fungi associated with two ecotypes of ragweed (Ambrosia artemisiifolia L.). Frontiers in Plant Science. 5:500. doi 10.3389/fpls.2014.00500.

Interpretive Summary: Growing awareness of herbicide resistant weeds may affect how they are controlled. Weed control may change since rising atmospheric CO2 can increase growth and may change effectiveness of herbicides. We grew common ragweed that were resistant or susceptible to Round-Up (glyphosate) in ambient and elevated CO2. High CO2 increased ragweed growth. Also, Round-Up resistant plants grew better regardless of CO2. A number of fungi were observed on ragweed, some of which can cause disease. Fungi were not affected by CO2 but were different on Round-Up resistant vs. susceptible plants. The common leaf disease powdery mildew was higher on Round-Up susceptible plants. Other differences in fungi were also found. This study is the first to report information on the effects of herbicide resistance and elevated CO2 on fungi associated with weeds. It is important to understand how herbicide resistance affects plant diseases and how rising atmospheric CO2 might change this in other important weeds and crops.

Technical Abstract: Herbicide resistant weed populations have developed due to the repeated application of herbicides. Elevated concentrations of atmospheric CO2 can have positive effects on weed growth, but how rising CO2 might affect herbicide resistant weeds is not known. Ragweed (Ambrosia artemisiifolia L.) ecotypes known to be resistant or susceptible to glyphosate herbicide were exposed to either ambient (375 CO2) or elevated (ambient + 200 CO2) concentrations of CO2 in open top chambers. Plants were harvested following 8 weeks of CO2 exposure when they began to exhibit disease symptoms including spots on leaves and stems. Elevated CO2 significantly increased top, root, and total plant biomass. Also, glyphosate resistant plants had significantly greater top, root, and total biomass than plants susceptible to the herbicide. There were no significant CO2 by ecotype interactions. Fungi from 13 genera were associated with ragweed; leaves yielded a greater number of fungal genera (8) than did stems or roots (5 each). Several of the fungi found can be either pathogens (i.e., Alternaria sp., Fusarium sp., Rhizoctonia sp.), aiding the decline in health of the ragweed plants, or saprophytes existing on dead plant tissues. The common foliar disease powdery mildew was significantly higher on susceptible compared with resistant ragweed. Susceptible plants also showed an increased frequency of Rhizoctonia on leaves and Alternaria on stems; however, Fuarium was observed more frequently on resistant ragweed leaves. Fungi were not affected by CO2 concentration or its interaction with plant genetics. This study reports the first information on the effects of herbicide resistance and elevated CO2 on fungi associated with weeds. How herbicide resistance affects plant diseases and how rising atmospheric CO2 might impact these affects needs to be addressed, not only with crops but also with important weeds.