Diversity of arbuscular mycorrhizal fungi in a long-term no-tillage onion production system

Onion is predominantly grown under conventional management. Alternatively, the no-tillage vegetable system uses cover crops to form a residue layer, which improves soil physical, chemical, and biological quality. Aiming to understand the effect of mycorrhizal and non-mycorrhizal cover crops on arbuscular mycorrhizal fungus diversity, we used morphological characterization of spores and high-throughput sequencing in soil from a long-term experiment with no-tillage onion. Treatments were black oats (Avena strigosa Schreb.); rye (Secale cereale L.); oilseed radish (Raphanus sativus L.); rye + oilseed radish; black oats + oilseed radish before the onion crop, and the control was a fallow area. In spring, all plots had onions, followed by velvet-bean in summer. Additionally, a conventional tillage system area and a forest, both adjacent to the experiment, were evaluated. Morphological identification of spores of arbuscular mycorrhizal fungi showed dominance of the Glomeraceae and Acaulosporaceae families. The DNA sequencing of rhizospheric soil confirmed those data and estimated 75 operational taxonomic units, with a predominance of the genus Glomus. Presence of oilseed radish, a non-mycorrhizal cover crop, did not reduce the occurrence of fungal species in relation to mycorrhizal cover crops. The use of different cover crop species in a long-term succession system maintains the natural mycorrhizal community.

Keywords
Allium cepa ; AMF; conventional tillage; cover crops; high-throughput sequencing; taxonomy