title: Arbuscular mycorrhiza reduces susceptibility of tomato to Alternaria solani.
abstract: Mycorrhiza frequently leads to the control of root pathogens, but appears to have the opposite effect on leaf pathogens. In this study, we studied mycorrhizal effects on the development of early blight in tomato (Solanum lycopersicum) caused by the necrotrophic fungus Alternaria solani. Alternaria-induced necrosis and chlorosis of all leaves were studied in mycorrhizal and non-mycorrhizal plants over time course and at different soil P levels. Mycorrhizal tomato plants had significantly less A. solani symptoms than non-mycorrhizal plants, but neither plant growth nor phosphate uptake was enhanced by mycorrhizas. An increased P supply had no effect on disease severity in non-mycorrhizal plants, but led to a higher disease severity in mycorrhizal plants. This was parallel to a P-supply-induced reduction in mycorrhiza formation. The protective effect of mycorrhizas towards development of A. solani has some parallels to induced systemic resistance, mediated by rhizobacteria: both biocontrol agents are root-associated organisms and both are effective against necrotrophic pathogens. The possible mechanisms involved are discussed.
authors.affiliation: Biometry and Population Genetics, Justus-Liebig-Universität Gießen, IFZ, Heinrich-Buff-Ring 26-32, 35392, Gießen, Germany. Maendy.Fritz@agrar.uni-giessen.de.
authors.forename: Maendy
authors.initials: M
authors.lastname: Fritz
authors.affiliation: Biosystems Department, Risø National Laboratory, Roskilde, Denmark.
authors.forename: Iver
authors.initials: I
authors.lastname: Jakobsen
authors.affiliation: Biosystems Department, Risø National Laboratory, Roskilde, Denmark.
authors.forename: Michael Foged
authors.initials: MF
authors.lastname: Lyngkjær
authors.affiliation: Department of Agricultural Sciences, The Royal Veterinary and Agricultural University, Copenhagen, Denmark.
authors.forename: Hans
authors.initials: H
authors.lastname: Thordal-Christensen
authors.affiliation: Biometry and Population Genetics, Justus-Liebig-Universität Gießen, IFZ, Heinrich-Buff-Ring 26-32, 35392, Gießen, Germany.
authors.forename: Jörn
authors.initials: J
authors.lastname: Pons-Kühnemann
mesh_terms: D000528:Alternaria / Q000254:growth & development* / Q000472:pathogenicity; D016014:Linear Models; D018551:Solanum lycopersicum; D038821:Mycorrhizae / Q000502:physiology*; D010935:Plant Diseases / Q000382:microbiology*; D018515:Plant Leaves / Q000382:microbiology; D011897:Random Allocation