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CO2 Enrichment Alleviates the Disease Severity of a Rice Pathogen

Paper Reviewed
da Rosa Dorneles, K., Martins, A.C., Fernando, J.A., do Amarante, L., de Avila, L.A., Deuner, S. and Dallagnol, L.J. 2020. Increased atmospheric CO2 concentration causes modification of physiological, biochemical and histological characteristics that affects rice-Bipolaris oryzae interaction. European Journal of Plant Pathology DOI: 10.1007/s10658-020-01972-4.

Brown spot is a grain yield-reducing disease in rice caused by the fungus Bipolaris oryzae. In the words of da Rosa Dorneles et al. (2020) it infects the panicle, "causing sterility of the floral organs, reduction of the green leaf area due to plant tissue chlorosis and necrosis, and reduction of photosynthesis, due both to impaired light capture ability and decreased mesophyll capacity to fix CO2," citing the works of Sunder et al. (2014) and Dallagnol et al. (2011).

Because brown spot is prevalent in all rice-growing regions and can reduce grain yields by 50% or more, there is considerable interest in learning how this disease might fare in a CO2-enriched world of the future, especially since multiple studies have shown a reduction in plant pathogen-related diseases under higher levels of CO2 (see, for example, the following links: Growth Response to CO2 with Other Variables (Disease: Agriculture, Other Crops) and Growth Response to CO2 with Other Variables (Disease: Agriculture, Legumes)). Such was the objective of da Rosa Dorneles et al. in a recent study published in the European Journal of Plant Pathology.

To accomplish their objective the seven Brazilian researchers grew two rice cultivars (BRS Querencia and Inov CL) in open-top chambers located on the Capão do Leão Campus of the Federal University of Pelotas (Capão do Leão, RS, Brazil) under ambient (400 ppm) or elevated (700 ppm) CO2 concentrations. At phenological stage V7-V8, the scientists inoculated the leaves on half of the plants in each CO2 treatment with Bipolaris oryzae, thereafter measuring disease severity at three different intervals post inoculation (3, 8 and 16 days after).

In describing their findings, da Rosa Dorneles et al. report that "plants at 700 ppm [CO2] showed lower severity of brown spot, regardless of the evaluation time, and smaller lesions at 16 days after inoculation, compared to the plants at 400 ppm CO2." Searching for the mechanism(s) behind this favorable outcome, the scientists observed a CO2-induced alteration of plant anatomic and photosynthetic characteristics, reporting "data from the present study indicate that the reduction of the parenchyma thickness and bulliform cell size and increase of carbohydrate concentration are related to the reduction of the severity of brown spot caused by B. oryzae in rice plants cultivated at 700 ppm CO2." Such positive changes in leaf morphological traits and carbohydrate accumulation are welcomed news in the future battle over rice brown spot. As the air's CO2 rises, the negative impacts of this disease will be reduced, translating to higher grain yields to feed an increasing world population.

Dallagnol, L.J., Rodrigues, F.A., Martin, S.C.V., Cavatte, P.C. and DaMatta, F.M. 2011. Alterations on rice leaf physiology during infection by Bipolaris oryzae. Australasian Plant Pathology 40: 360-365.

Sunder, S., Singh, R. and Agarwal, R. 2014. Brown spot of rice: An overview. Indian Phytopathology 67: 201-215.

Posted 17 July 2020