Photosynthetic response of citrus to Citrus tristeza virus isolates with potential for cross-protection

The objective of this work was to evaluate the photosynthetic response of citrus varieties to the inoculation of isolates T30 and T3 of Citrus tristeza virus (CTV) characterized as having potential to provide cross-protection against severe CTV isolates in citrus. Citrus plants of 'Campbell' orange, 'Persian' lime, and 'Key' lime were subjected to inoculations by both isolates by patch. Noninoculated plants were used as the control. Symptom expression, photosynthetic and transpiration rates, and stomatal conductance were evaluated by IRGA. Stomatal density and size were evaluated by epidermal impressions. The CTV isolates were also evaluated and molecularly characterized by RT-PCR and Sanger sequencing. 'Campbell' orange and 'Persian' lime plants remained asymptomatic after the inoculations. The inoculation treatments with both CTV isolates did not reduce photosynthetic capacity, transpiration rate, and stomatal conductance, in comparison with the control. Stomatal density and size varied according to the citrus species. T30 and T3 do not affect the photosynthetic responses of 'Campbell' orange and 'Persian' lime; therefore, these isolates have the potential to provide cross-protection to citrus varieties against severe isolates of CTV.