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Front. Plant Sci. | doi: 10.3389/fpls.2018.01396

Defense compounds rather than nutrient availability shape aggressiveness trait variation along a leaf maturity gradient in a biotrophic plant pathogen

 Agathe Maupetit1,  Romain Larbat2,  Michaël Pernaci1, Axelle Andrieux1,  Cécile Guinet3, Anne-Laure Boutigny3, Bénédicte Fabre1,  Pascal Frey1 and  Fabien Halkett1*
  • 1IAM, INRA Centre Nancy Grand Est, France
  • 2Université de Lorraine, France
  • 3Unité de Mycologie, ANSES, France

Foliar pathogens face heterogeneous environments depending on the maturity of leaves they interact with. In particular, nutrient availability as well as defense levels may vary significantly, with opposing effects on the success of infection. The present study tested which of these factors have a dominant effect on the pathogen’s development. Poplar leaf disks of eight maturity levels were inoculated with the poplar rust fungus Melampsora larici-populina using an innovative single-spore inoculation procedure. A set of quantitative fungal traits (infection efficiency, latent period, uredinia size, mycelium quantity, sporulation rate, sporulation capacity and spore volume) was measured on each infected leaf disk. Uninfected parts of the leaves were analyzed for their nutrient (sugars, total C and N) and defense compounds (phenolics) content. We found that M. larici-populina is more aggressive on more mature leaves as indicated by wider uredinia and a higher sporulation rate. Other traits varied independently from each other without a consistent pattern. None of the pathogen traits correlated with leaf sugar, total C, or total N content. In contrast phenolic contents (flavonols, hydroxycinnamic acid esters and salicinoids) were negatively correlated with uredinia size and sporulation rate. The pathogen’s fitness appeared to be more constrained by the constitutive plant defense level than limited by nutrient availability, as evident in the decrease in sporulation.

Keywords: Constitutive defense, aggressiveness traits, plasticity, nutrient availability, rust fungus

Received: 20 Apr 2018; Accepted: 03 Sep 2018.

Edited by:

Christophe Le May, Agrocampus Ouest, France

Reviewed by:

Sabine Banniza, University of Saskatchewan, Canada
FOURNET Sylvain, Institut National de la Recherche Agronomique (INRA), France  

Copyright: © 2018 Maupetit, Larbat, Pernaci, Andrieux, Guinet, Boutigny, Fabre, Frey and Halkett. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: PhD. Fabien Halkett, INRA Centre Nancy Grand Est, IAM, Nancy, France, fabien.halkett@inra.fr