© New Phytologist (2002) 154: 461– 470 www.newphytologist.com 461 Research Blackwell Science Ltd Limitations to photosynthesis in tomato leaves induced by Fusarium wilt Salvador Nogués 1 , Lurdes Cotxarrera, Leonor Alegre and Maria Isabel Trillas Departament de Biologia Vegetal, Universitat de Barcelona, Av. Diagonal 645, E-08028 Barcelona, Spain; 1Present address: Laboratoire d’Ecophysiologie Végétale (BAT 362), Université Paris-XI, 91405 Orsay, Cedex France Summary • The effects are reported here of inoculation with the soil-borne pathogen Fusarium oxysporum f. sp. lycopersici race 1 (FOL-1) on the photosynthetic capacity of tomato plants (Lycopersicon esculentum cv. Roma). • Plants were grown in cork compost with a pathogen concentration of c. 1 × 10 5 cfu ml –1 , or without the fungus, for 31 d in controlled environmental chambers. Noninoculated plants were also subjected to progressive drought by withholding water. • During the first stage of disease development, FOL-1 wilt decreased the light-saturated rate of CO 2 assimilation. This was accompanied by a decrea- ses in the maximum carboxylation velocity and the capacity for ribulose-1,5- bisphophate regeneration, in the absence of any significant photodamage to PSII, and increased stomatal limitation of the CO 2 supply. As the disease progressed, the maximum quantum efficiency of PSII photochemistry decreased in the leaves. FOL-1 wilt also decreased leaf area, therefore a reduction in the ability of the tomato plants to capture photosynthetically active radiation is also a major factor in determining the depression in the photosynthetic productivity of these infected plants. • The effect of the infection by FOL-1 on leaf photosynthesis was mimicked by water stress. Key words: chlorophyll fluorescence, Fusarium oxysporum, Lycopersicon esculentum (tomato), photorespiration, photosynthesis, vascular wilt. Abbreviations A, net CO 2 assimilation rate; A sat , light-saturated net CO 2 assimilation rate; c., ambi- ent CO 2 concentration; cfu, colony-forming units; c i , intercellular CO 2 concentra- tion; Fo′, minimum fluorescence yield in light-adapted state; FOL-1, Fusarium oxysporum Schlecht. f. sp. lycopersici race 1; Fv/Fm, maximum efficiency of PSII photochemistry after dark-adaptation; Fv′/Fm′, efficiency of energy capture by open PSII reaction centres; φ PSII , quantum yield of PSII electron transport; φ CO 2 , quantum efficiency of CO 2 assimilation; g s , stomatal conductance; J max , maximum potential rate of electron transport contributing to RuBP regeneration; l, stomatal limitation to A sat ; P i chloroplastic inorganic phosphate; PPFD, photosynthetically active photon flux density; q p , photochemical quenching; RuBP, ribulose 1,5- bisphosphate; RWC, relative leaf water content; SBPase, sedoheptulose 1,7- bisphosphate; V c,max , maximum carboxylation velocity of Rubisco; VPD, leaf to air vapour pressure difference; ψ w , leaf water potential. © New Phytologist (2002) 154: 461– 470 Author for correspondence: Salvador Nogués Tel: +34 93 4021480 Fax: +34 93 4112842 Email: nogus@porthos.bio.ub.es Received: 18 October 2001 Accepted: 9 January 2002