Relevance of mycorrhizal fungal origin and host plant genotype to inducing growth and nutrient uptake in Medicago species

This study reports the effects of three selected arbuscular mycorrhizal- (AM-) forming species (Glomus mosseae, Glomus fasciculatum or Glomus caledonium) in comparison with autoctone endophytes by determining changes in plant growth, nutritional and symbiotic parameters in four species of Medicago: M. trunculata, M. rigidula, M. polimorpha and M. rotata, The relative susceptibility to and dependence upon AM fungi of Medicago species was also evaluated. Results showed a high functional compatibility between Medicago species and autoctone endophytes, and a specific plant response to individual Glomus species. Differences among the Medicago species in their reaction to Glomus species ranged from negative to highly positive. A combination of host and AM fungal species indicates that a specific compatibility exists among symbionts. Nutrient uptake as a result of AM colonization also indicated a wide degree of responsiveness in each species according to the associated fungal symbiont to the plant, A positive effect on N, P and K, and negative on Ca and Mg nutrition was found in all mycorrhizal treatments, especially with the autoctone endophytes. Mycorrhizal infectivity could not be related to endophyte effectiveness, with generally fewer and larger Rhizobium nodules found on the most effective mycorrhizal treatments. Results support the role of indigenous AM endophytes in the efficacy of mycorrhizal symbiosis and the importance of host-endophyte selection to maximize growth and nutrition of Medicago. This study shows that AM symbiotic efficiency attributed to Medicago is dependent on endophyte association and plant species. The importance of selecting suitable AM fungi is of practical interest for improving the effectiveness of the tripartite symbiosis.