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 mycorrhiza l- (AM-) forming species (Glomus mosseae, Glomus fasciculatum or Glomu s caledonium) in comparison with autoctone endophytes by determining c hanges in plant growth, nutritional and symbiotic parameters in four s pecies of Medicago: M. trunculata, M. rigidula, M. polimorpha and M. r otata, 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 amo ng the Medicago species in their reaction to Glomus species ranged fro m negative to highly positive. A combination of host and AM fungal spe cies indicates that a specific compatibility exists among symbionts. N utrient uptake as a result of AM colonization also indicated a wide de gree of responsiveness in each species according to the associated fun gal symbiont to the plant, A positive effect on N, P and K, and negati ve on Ca and Mg nutrition was found in all mycorrhizal treatments, esp ecially with the autoctone endophytes. Mycorrhizal infectivity could n ot be related to endophyte effectiveness, with generally fewer and lar ger Rhizobium nodules found on the most effective mycorrhizal treatmen ts. Results support the role of indigenous AM endophytes in the effica cy of mycorrhizal symbiosis and the importance of host-endophyte selec tion to maximize growth and nutrition of Medicago. This study shows th at AM symbiotic efficiency attributed to Medicago is dependent on endo phyte association and plant species. The importance of selecting suita ble AM fungi is of practical interest for improving the effectiveness of the tripartite symbiosis.