Evaluating the stability of nursery-established arbuscular mycorrhizal fungal associations in apple rootstocks

Authors: ZHANG, HUITING - Washington State University; WANG, WANYAN - Pennsylvania State University; Honaas, Loren; MAZZOLA, MARK - Stellenbosch University; Somera, Tracey

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Arbuscular mycorrhizal fungi (AMF) are promoted as bioinoculants for sustainable agriculture. Little is known, however, about the survival of AMF inoculants in orchard soil and their impacts on native or pre-established AMF communities in root tissue. The current study was designed to assess this in apple. An additional aim of this study was to explore the effect of apple rootstock genotype on AMF community structure. A greenhouse experiment was conducted in which a variety of apple rootstock genotypes (G.890, G.935, M.26 and M.7) were inoculated with a commercially available, multi-species AMF consortium. Pre-existing (nursery-derived) AMF communities were sequenced and changes to AMF community structure following cultivation in pasteurized soil (inoculated and non-inoculated) were assessed. Phylogenetic analysis showed that the inoculant colonization potential was limited and that apple rootstocks serve as a significant source of inoculum from the nursery where they are produced. Claroideoglomus spp. contained in the inoculant were, however, capable of infecting both M.26 and M.7 rootstocks. It was also found that the inoculant altered resident AMF communities regardless of colonization success. The rootstock most sensitive to changes in AMF community structure was M.26. Phylogenetic analysis also revealed that the commercial inoculant contained a very different consortium of AMF than expected, highlighting the importance of using phylogenetic-based classification for accurate characterization of AMF communities. In addition, phylogenetic analysis identified a new, unique group of AMF of unknown taxonomy. A better understanding of what “real” AMF communities look like in orchard systems will be an essential component to the successful transfer of compatible rootstock/AMF combinations from lab to field.

Technical Abstract: Arbuscular mycorrhizal fungi (AMF) are promoted as commercial biofertilizers (bioinoculants) for sustainable agriculture. Little is known, however, about the survival of AMF inoculants in soil and their impacts on native or pre-established AMF communities in root tissue. The current study was designed to assess the stability of pre-existing/nursery-derived AMF in apple rootstocks after being planted into soil containing a known community of AMF with a limited number of species. In orchard systems, root-associated endophytic communities (bacteria and fungi) are known to differ depending on apple rootstock genotype and soil-type. Thus, an additional aim of this study was to explore the effect of apple rootstock genotype on AMF community structure. A greenhouse experiment was conducted in which a variety of apple rootstock genotypes (G.890, G.935, M.26 and M.7) were inoculated with a commercially available, multi-species AMF consortium. Nursery-derived AMF communities were sequenced and changes to AMF community structure following cultivation in pasteurized soil (inoculated and non-inoculated) were assessed. In order to accurately assign high throughput sequencing data to the species level, a Glomermycota-specific phylogenetic tree was constructed. Phylogenetic analysis showed that inoculant colonization potential was limited and that the rootstock serves as a significant source of nursery-derived AMF inoculum. Claroideoglomus spp. contained in the inoculant were, however, capable of infecting both M.26 and M.7 rootstocks. It was also found that the inoculant caused alterations (taxa suppression and/or stimulation) to the resident AMF communities of both Geneva and Malling rootstocks, regardless of colonization success. The impact on specific members of the resident AMF communities varied according to rootstock genotype. The rootstock most sensitive to changes in AMF community structure was M.26. Phylogenetic analysis also revealed that the commercial inoculant contained a very different consortium of AMF than expected. Tree-based analysis identified a unique, well-supported clade of unknown taxonomy, highlighting the importance of using phylogenetic-based classification for accurate characterization of AMF communities.