Identification of arbuscular mycorrhizal fungi species preferentially associated with grapevine roots inoculated with commercial bioinoculants 

Abstract

Context and purpose of the study – Arbuscular mycorrhizal fungi (AMF) form symbiotic associations with plant roots and can help plants acquire nutrients from the soil in exchange for photosynthetic carbon. Commercial bioinoculants containing AMF are widely available and represent a potential opportunity to reduce the dependence of grapevines on agrochemicals. However, which commercially available AMF species colonize vine roots and affect vine growth remains unknown. The aim of this study was to identify the AMF species from commercial bioinoculants that colonize grapevine roots using high-throughput sequencing, and to evaluate the performance of five commercial bioinoculants and their effects on own-rooted Cabernet sauvignon.

Material and methods – Two-year-old own-rooted Cabernet sauvignon vines were potted into a non-sterile orchard-collected soil and placed in a greenhouse. The silt loam soil was low in available nitrogen, phosphorus, potassium and organic matter and had a neutral pH.  Pots were inoculated with one of five commercial bioinoculants. Root length colonized by AMF, petiole nitrogen concentration, plant biomass and root morphology were evaluated. The  AMF community present in the grapevine roots growing in non-inoculated (control) and inoculated soil were profiled using high-throughput sequencing of 18S and ITS2 rRNA gene regions.

Results – The proportion of roots colonized with AMF fungal structures significantly increased for plants in inoculated soil, but the degree of colonization differed among commercial bioinoculants. Petiole nitrogen concentration increased and carbon to nitrogen ratio decreased for plants in inoculated soil. Shoot and root dry weight were increased for plants in inoculated soil when compared with plants in non-inoculated soil. Root diameter decreased and root length density and specific root length increased with greater AMF root colonization for plants in inoculated soil. The most predominant genus of AMF species from commercial bioinoculants colonizing roots in the inoculated soil was Rhizophagus, Glomus and Funneliformis, while Diversispora, Paraglomus, and Mortierella showed a low relative abundance respectively. A high relative abundance of the genus Glomus and Rhizophagus were found in roots of plants growing in the non-inoculated soil controls while Funneliformis, Paraglomus and Mortierella  were less predominant. Interestingly the  endophytic fungus Mortierella from the order Mortierellales is considered as a beneficial root colonizing fungus. These results suggest that the native AMF community of non-inoculated soil controls had limited effect on grapevine adaptative traits while inoculated soil with commercial bioinoculants containing specific species from the genus Glomus and Rhizophagus can modify root traits under soil nutrient deficiency and may be considered an alternative to replace chemical fertilizers .