Elevation in atmospheric CO(2) concentration broadly affects plant phenology and physiology, and these effects may alter the performance of plant viruses. The effects of elevated CO(2) on the susceptibility of tomato plants to Tomato yellow leaf curl virus (TYLCV) were examined for two successive years in open top chambers (OTC) in the field. We experimentally tested the hypothesis that elevated CO(2) would reduce the incidence and severity of TYLCV on tomato by altering plant defence strategies. Our results showed that elevated CO(2) decreased TYLCV disease incidence (by 14.6% in 2009 and 11.8% in 2010) and decreased disease severity (by 20.0% in 2009 and 10.4% in 2010). Elevated CO(2) also decreased the level of TYLCV coat protein in tomato leaves. Regardless of virus infection, elevated CO(2) increased plant height and aboveground biomass. Additionally, elevated CO(2) increased the leaf C:N ratio of tomato, but decreased soluble protein content in leaves. Notably, elevated CO(2) increased the salicylic acid (SA) level in uninfected and infected plants. In contrast, elevated CO(2) reduced jasmonic acid (JA) in uninfected plants while it increased JA and abscisic acid (ABA) in virus-infected plants. Furthermore, combined exogenous SA and JA application enhanced resistance to TYLCV more than application of either SA or JA alone. Our results suggest that the modulated antagonistic relationship between SA and JA under elevated CO(2) makes a great contribution to increased tomato resistance to TYLCV, and the predicted increases in tomato productivity may be enhanced by reduced plant virus susceptibility under projected rising CO(2) conditions.

AMF-arbuscular mycorrhizal fungi; Ca-ambient CO2 concentration; Ci-intercellular CO2 concentration; Chlchlorophyll; DM-dry mass; F0-minimal fluorescence yield of the dark-adapted state; F0'-minimal fluorescence yield of the lightadapted state; Fm-maximal fluorescence yield of the dark-adapted state; Fm'-maximal fluorescence yield of the light-adapted state; Fs-steady-state fluorescence yield; Fv/Fm-maximal quantum yield of PSII photochemistry; Fv'/Fm'-maximum efficiency of PSII; FM-fresh mass; gs-stomatal conductance; Ls-stomatal limitation; NPQ-nonphotochemical quenching; PN-net photosynthetic rate; ROS-reactive oxygen species; qP-photochemical quenching coefficient; ФPSII-effective quantum yield of PSII photochemistry.