Arbuscular Mycorrhizal symbiosis in four Al-tolerant wheat genotypes grown in an acidic Andisol

Arbuscular mycorrhizal (AM) fungi play an important role in protecting host plant against phytotoxic aluminum (Al) in soil. The aim of this work was to analyze the effect of AM fungi native from acid soil on the growth of four Al-tolerant wheat (Triticum aestivum L.) genotypes. A greenhouse experiment was conducted using three near isogenic Chilean wheat genotypes ('Crac', 'Invento' and 'Otto') and one of recognized Al-tolerance ('Atlas 66') which were grown in an acid Andisol with 34% Al-saturation. The plant dry biomass and root colonization were determined at six early growth stages and AM spore density, glomalin (as GRSP) and acid phosphatase (P-ase) activity were analyzed at two stages; i) 11 days after sowing -DAS-, and at 60 DAS. Results showed that in all genotypes AM root colonization was not inhibited in spite of high soil Al saturation in the soil and a significant root colonization degree was observed at the first phenological stage mainly in the native wheat genotypes. Also, 'Crac' and 'Invento' genotypes showed the highest densities of AM spores and GRSP production. All wheat cultivars increased the P-ase activity overtime. Root biomass correlated positive and significantly with root colonization (r=0.71; P<0.001) and inversely with AM spores (r=-0.61; P<0.001). 'Atlas 66' showed a high adaptability to grow in acid conditions but produced the lesser amounts of AM propagules, which suggest that this genotype would show Al-tolerance mechanisms not fully associated to AM symbiosis as the Chilean wheat cultivars do. In conclusion, the higher early root colonization, AM spores and GRSP production associated to native wheat genotypes could indicate that AM symbiosis play a principal role in the Al tolerance capacity of T. aestivum developed in those soils with high Al levels and fungal native populations adapted to this conditions.