The Contrasting Effects of Elevated CO2 on TYLCV Infection of Tomato Genotypes with and without the Resistance Gene, Mi-1.2

Abstract

Elevated atmospheric CO₂ typically enhances photosynthesis of C3 plants and alters primary and secondary metabolites in plant tissue. By modifying the defensive signaling pathways in host plants, elevated CO₂ could potentially affect the interactions between plants, viruses, and insects that vector viruses. <i>R</i> gene-mediated resistance in plants represents an efficient and highly specific defense against pathogens and herbivorous insects. The current study determined the effect of elevated CO₂ on tomato plants with and without the nematode resistance gene <i>Mi-1.2</i>, which also confers resistance to some sap-sucking insects including whitefly, <i>Bemisia tabaci</i>. Furthermore, the subsequent effects of elevated CO₂ on the performance of the vector whiteflies and the severity of <i>Tomato yellow leaf curl virus</i> (TYLCV) were also determined. The results showed that elevated CO₂ increased the biomass, plant height, and photosynthetic rate of both the Moneymaker and the <i>Mi-1.2</i> genotype. Elevated CO₂ decreased TYLCV disease incidence and severity for Moneymaker plants but had the opposite effect on <i>Mi-1.2</i> plants whether the plants were agroinoculated or inoculated via <i>B. tabaci</i> feeding. Elevated CO₂ increased the salicylic acid (SA)-dependent signaling pathway on Moneymaker plants but decreased the SA-signaling pathway on <i>Mi-1.2</i> plants when infected by TYLCV. Elevated CO₂ did not significantly affect <i>B. tabaci</i> fitness or the ability of viruliferous <i>B. tabaci</i> to transmit virus regardless of plant genotype. The results indicate that elevated CO₂ increases the resistance of Moneymaker plants but decreases the resistance of <i>Mi-1.2</i> plants against TYLCV, whether the plants are agroinoculated or inoculated by the vector. Our results suggest that plant genotypes containing the R gene <i>Mi-1.2</i> will be more vulnerable to TYLCV and perhaps to other plant viruses under elevated CO₂ conditions.