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Effects of Elevated Atmospheric CO₂ Concentration on the Infection of Rice Blast and Sheath Blight

First, second, and fifth authors: National Agricultural Research Center for Tohoku Region, Iwate 020-0198, Japan; third author: National Agricultural Research Center for Kyushu Okinawa Region, Kumamoto 861-1192, Japan; fourth author: College of Agriculture and Life Science, Chonnam National University, 300 Yongbong-dong, Buk-gu, Gwangju 500-757, South Korea; and sixth author: The University of Tokyo, Tokyo 116-8657, Japan

The effect of elevated atmospheric CO₂ concentration on rice blast and sheath blight disease severity was studied in the field in northern Japan for 3 years. With free-air CO₂ enrichment (FACE), rice plants were grown in ambient and elevated (≈200 to 280 μmol mol^-1 above ambient) CO₂ concentrations, and were artificially inoculated with consist of Magnaporthe oryzae. Rice plants grown in an elevated CO₂ concentration were more susceptible to leaf blast than those in ambient CO₂ as indicated by the increased number of leaf blast lesions. Plants grown under elevated CO₂ concentration had lower leaf silicon content, which may have contributed to the increased susceptibility to leaf blast under elevated CO₂ concentrations. In contrast to leaf blast, panicle blast severity was unchanged by the CO₂ enrichment under artificial inoculation, whereas it was slightly but significantly higher under elevated CO₂ concentrations in a spontaneous rice blast epidemic. For naturally occurring epidemics of the sheath blight development in rice plants, the percentage of diseased plants was higher under elevated as opposed to ambient CO₂ concentrations. However, the average height of lesions above the soil surface was similar between the treatments. One hypothesis is that the higher number of tillers observed under elevated CO₂ concentrations may have increased the chance for fungal sclerotia to adhere to the leaf sheath at the water surface. Consequently, the potential risks for infection of leaf blast and epidemics of sheath blight would increase in rice grown under elevated CO₂ concentration.

Additional keywords: Pyricularia oryzae , Rhizoctonia solani .