VIEW ARTICLE

Gas Exchange Studies on the Transpiration and Photosynthesis of Tomato Leaves Affected by Fusarium oxysporum f. sp. lycopersici. J. M. Duniway, National Science Foundation Postdoctoral Fellow, Research School of Biological Sciences, Australian National University, Box 475, Canberra, A.C.T. 2601, Australia, Present address of senior author: Department of Plant Pathology, University of California, Davis 95616; R. O. Slatyer, Professor, Research School of Biological Sciences, Australian National University, Box 475, Canberra, A.C.T. 2601, Australia. Phytopathology 61:1377-1381. Accepted for publication 25 June 1971. DOI: 10.1094/Phyto-61-1377.

Leaves of Bonny Best tomato plants were used for gas exchange measurements at various times after root inoculation with Fusarium oxysporum f. sp. lycopersici race 1. Simultaneous measurements of transpiration and photosynthesis, under conditions of CO₂ limitation and light saturation, allowed the calculation of stomatal and intracellular resistances to CO₂ diffusion. Photosynthesis and transpiration were unaffected by the host-pathogen interaction until 15 days after inoculation, when there were marked reductions in both. The reduction in photosynthesis was caused in part by an increase in stomatal resistance and in part by a large increase in intracellular resistance. Measurements of leaf water content and water potential indicated that the increases in stomatal and intracellular resistances preceded the onset of water stress in a given leaf. After the host-pathogen interaction had caused some water stress to occur in a leaf, the intracellular resistance became nearly infinite. Comparable levels of water stress had little effect on the intracellular resistance of healthy leaves. The increase in intracellular resistance of infected leaves was associated with reductions in both dark respiration and photorespiration, but was not associated with a decrease in the activity of ribulose diphosphate carboxylase.