Detection of arbuscular mycorrhizal fungi associated with pecan (Carya illinoinensis) trees by molecular and morphological approaches

Abstract

Arbuscular mycorrhizal (AM) fungal community associated with pecan (Carya illinoinensis) roots and rhizospheric soils was assessed by spore isolation and morphological characterisation and by pyrosequencing of AM molecular markers. The AM fungal community associated with pecan growing in the field, was always more diverse than that associated with pecan growing in containers. This was not observed when AM richness was studied, suggesting that soil disturbance by a reduction in host plant richness leads to a less equitable distribution of AM fungal species, in contrast to natural soils. The chosen primers (AMV4.5F/AMDGR) for pyrosequencing showed high AM fungal specificity. Based on 97% sequence similarity, 49 operational taxonomic units (MOTUs) were obtained and, amongst these, 41 MOTUs corresponded to the Glomeromycota phylum. The number of obtained AM sequences ranged from 2164, associated with field samples, to 5572 obtained from pecan trap pot culture samples, defining 30 and 29 MOTUs, respectively. Richness estimated by conventional species identification was 6 and 9 AM fungal species in soil and pot samples, respectively. Claroideoglomus lamellosum, Funneliformis mosseae and Entrophospora infrequens were the only taxa detected using both techniques. Predominant sequences in the pecan rhizosphere samples, such as Rhizoglomus irregulare and other less abundant (Dominikia iranica, Dominikia indica, Sclerocystis sinuosa, Paraglomus laccatum), were detected only by pyrosequencing. Detection of AM fungal species based on spore morphology, in combination with molecular approaches, provides a more comprehensive estimate of fungal community composition.