Transpiration rate and stomatal parameters of transgenic papaya conferred with papaya ringspot virus resistance

A Biosafety Level 2 (BL2) greenhouse study was conducted at the Institute of Plant Breeding, University of the Philippines Los Banos, College, Laguna, Philippines from June 2007 to April 2008, to determine if the conferment of papaya (Carica papaya L.) ringspot virus (PRSV) resistance will affect the transpirational water loss of transgenic lines (132-2.9-13.27-7, 124-3.9-21.30-9 and 132-2.17-12.37), with reference to the non-transgenic control ('Solo 7-8' from Davao, Philippines). Comparative parameters were transpiration rate; stomatal conductance and stomatal density. Transpiration rate and stomatal conductance were measured at 1.5, 3, 5 and 9 months after planting (MAP). Stomatal density was measured at 9 MAP. Total green leaf area and specific leaf area were also measured at 1.5, 3 and 5 MAP. Transpiration rates and stomatal conductance did not differ among transgenic lines and between transgenic lines and non-transgenic control at 1.5, 3 and 5 MAP. Stomatal density and transpiration rate as well as stomatal density and conductance were loosely related. These are consistent with the insignificant differences in stomatal density, transpiration rate and stomatal conductance of the papaya transgenic lines and non-transgenic control. The conferment of PRSV resistance did not affect the instantaneous amount of water transpired on per unit leaf area-basis, and the water conducting property of stomates in transgenic lines. The insignificant difference in leaf area (total green leaf area) and leaf thickness (specific leaf area) further strengthened the insignificant differences observed in transpirational water loss between transgenic lines and non-transgenic control. The results imply that the water use of the transgenic lines was not altered.