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Weeds, Pests & Pathogens Beware: The Air's CO2 Content is Rising

Paper Reviewed
Goufo, P., Pereira, J., Moutinho-Pereira, J., Correia, C.M., Figueiredo, N., Carranca, C.,Rosa, E.A.S. and Trindade, H. 2014. Rice (Oryza sativa L.) phenolic compounds under elevated carbon dioxide (CO2) concentration. Environmental and Experimental Botany 99: 28-37.

In introducing their study of the subject, Goufo et al. note that crop plants need phenolic compounds "for structural support, constitutive and induced protection and defense against weeds, pathogens and insects," citing Jones and Hartley (1999). And they note, in this regard, that carbon dioxide is one of the four major raw materials that plants need in order to produce phenolic compounds, the other three being water, nutrients and light, additionally citing Bryant et al. (1983), Coley et al. (1985) and Herms and Mattson (1992).

With the objective to learn how the ongoing rise in the atmosphere's CO2 concentration might influence the production of phenolics in rice - one of the world's most important food crops - the eight Portuguese scientists conducted a two-year field study of a japonica rice variety (Oryza sativa L. cv. Ariete) that employed open-top chambers maintained at either 375 or 550 ppm CO2 over two entire life cycles of the crop, during which time numerous plant samples were collected at five different growth stages and assessed for occurrence and amounts of many plant-produced substances, including phenolics.

This work revealed, according to Goufo et al., that "during the early stages of plant development, photosynthates were mainly used to synthesize proteins and meet the growth demand of the plant," while the normal occurrence of growth reduction typically experienced at maturity "made more resources available for the synthesis of phenolic compounds." And they further report, in this regard, that all plant organs had higher levels of phenolic acids and flavonoids in response to "CO2 enrichment during the maturity stages."

As for the significance of these findings, the eight researchers write that "phenolic compounds are emerging as important defense compounds in rice," particularly noting that the phenolic compound tricin "inhibits the growth of Echinochloa colonum, Echinochloa crusgalli, Cyperus iris and Cyperus difformis," which they say "are the most noxious weeds in rice fields," citing Kong et al. (2004). And they add that several flavonoids "have also been found to exhibit antibiotic activities against the soil-borne pathogenic fungi Rhizoctonia solani and Fusarium oxysporum," which they say are "the causal agents of rice seedling rot disease," again citing Kong et al. (2004), as well as Olofsdotter et al. (2002). And they thus suggest that the ongoing rise in the air's CO2 concentration may well "increase plant resistance to specific weeds, pests and pathogens," which should be great news for rice growers.

References
Bryant, J.P., Chapin III, F.S. and Klein, D.R. 1983. Carbon-nutrient balance of boreal plants in relation to vertebrate herbivory. Oikos 40: 357-368.

Coley, P.D., Bryant, J.P. and Chapin III, F.S. 1985. Resource availability and plant antiherbivore defense. Science 230: 895-899.

Herms, D.A. and Mattson, W.J. 1992. The dilemma of plants: to grow or defend. Quarterly Review of Biology 67: 283335.

Jones, C.G. and Hartley, S.E. 1999. A protein competition model of phenolic allocation. Oikos 86: 27-44.

Kong, C., Xu, X., Zhou, B., Hu, F., Zhang, C. and Zhang, M. 2004. Two compounds from allelopathic rice accession and their inhibitory activity on weeds and fungal pathogens. Phytochemistry 65: 1123-1128.

Olofsdatter,M., Jensen,L.B. and Courtois, B. 2002. Improving crop competitive ability using allelopathy - an example from rice. Plant Breeding 121: 1-9.

Posted 3 December 2014