Symbiotic performance of diverse Frankia strains on salt-stressed Casuarina glauca and Casuarina equisetifolia plants
2016
Ngom, Mariama | Gray, Krystelle | Diagne, Nathalie | Oshone, Rediet | Fardoux, Joël | Gherbi, Hassen | Hocher, Valérie | Svistoonoff, Sergio | Laplaze, Laurent | Tisa, Louis S. | Sy, Mame O. | Champion, Antony | LMI Adaptation des Plantes et microorganismes associés aux Stress Environnementaux [Dakar] (LAPSE) ; Institut de Recherche pour le Développement (IRD) | Université Cheikh Anta Diop de Dakar [Sénégal] (UCAD) | Diversité, adaptation, développement des plantes (UMR DIADE) ; Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD [Occitanie]) | Institut sénégalais de recherches agricoles [Dakar] (ISRA) | Department of Molecular, Cellular, and Biomedical Sciences ; University of New Hampshire (UNH) | Laboratoire des symbioses tropicales et méditerranéennes (UMR LSTM) ; Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Université Montpellier 1 (UM1)-Institut de Recherche pour le Développement (IRD)-Institut National de la Recherche Agronomique (INRA)-Université Montpellier 2 - Sciences et Techniques (UM2)-Université de Montpellier (UM)-Institut national d’études supérieures agronomiques de Montpellier (Montpellier SupAgro)
Symbiotic nitrogen-fixing associations between Casuarina trees and the actinobacteria Frankia are widely used in agroforestry in particular for salinized land reclamation. The aim of this study was to analyze the effects of salinity on the establishment of the actinorhizal symbiosis between C. glauca and two contrasting Frankia strains (salt sensitive; Ccl3 vs. salt tolerant; CeD) and the role of these isolates in the salt tolerance of C. glauca and C. equisetifolia plants. We show that the number of root nodules decreased with increasing salinity levels in both plants inoculated with Ccl3 and CeD. Nodule formation did not occur in seedlings inoculated with Ccl3 and CeD, at NaCl concentrations above 100 and 200 mM, respectively. Salinity also affected the early deformation of plant root hairs and reduced their number and size. In addition, expression of symbiotic marker Cg12 gene, which codes for a subtilase, was reduced at 50 mM NaCl. These data suggest that the reduction of nodulation in C. glauca under salt stress is in part due to inhibition of early mechanisms of infection. We also show that prior inoculation of C. glauca and C. equisetifolia with Frankia strains Ccl3 and CeD significantly improved plant height, dry biomass, chlorophyll and proline contents at all levels of salinity tested, depending on the Casuarina-Frankia association. There was no correlation between in vitro salt tolerance of Frankia strains and efficiency in planta under salt stressed conditions. Our results strongly indicate that increased N nutrition, photosynthesis potential and proline accumulation are important factors responsible for salt tolerance of nodulated C. glauca and C. equisetifolia.
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