Manioc (Manihot esculenta Crantz) is an important tropical crop that depends on arbuscular mycorrhizal (AM) association for its nutrition. However, little is known about the richness and species composition of AM fungal communities associating with manioc and possible differences across soils and manioc landraces. We studied the diversity and composition of AM fungal communities present in the roots of different manioc landraces and surrounding soils in indigenous shifting cultivation fields on different Amazonian soil types. A total of 126 AM fungal virtual taxa (VT; phylogenetically defined taxonomic units) were recovered from soil and root samples using 454 sequencing of AM fungal SSU rRNA gene amplicons. Different AM fungal communities occurred in different soil types. Minor differences occurred in the composition of AM fungal community associating with different manioc landraces, but AM fungal richness was not different among them. There was a low similarity between the AM fungal communities colonizing manioc roots and those recorded in the soil, independently of differences in soil properties or the manioc landrace evaluated. Rhizophagus manihotis and Glomus VT126 were the most abundant AM fungal species colonizing manioc roots. Contrasting with the results of earlier spore-based investigations, all the AM fungi identified as indicator species of particular manioc landraces were morphologically unknown Glomus species. In conclusion, different manioc landraces growing in common conditions associated with distinct AM fungal communities, whereby AM fungal communities in soils did not necessarily reflect the AM fungal communities colonizing manioc roots.
Keywords: Amazon region; Arbuscular mycorrhizal fungal virtual taxa; Cassava; Manihot esculenta; Shifting agriculture.