Effects of beneficial endophytic fungal inoculants on plant growth and nutrient absorption of trifoliate orange seedlings

•Effects of symbiotic AM fungi and AM like fungi on trifoliate orange were studied.•Piriformospora indica and AMF coexisted in roots, but the colonization was inferior.•Single or dual inoculation increased plant growth and affected root nutrients.•P increase in inoculated plants was associated with soil phosphatase and PT gene.•Piriformospora indica has more applied value in citrus than AMF as a biofertilizer. Citrus plants heavily depend on soil arbuscular mycorrhizal fungi (AMF), while the application of AMF in citrus is limited because of no propagation in vitro. The present work tried to apply a culturable (in vitro) endophytic fungus Piriformospora indica into trifoliate orange (Poncirus trifoliata) and to compare the role of P. indica in plant growth and nutrient acquisition especially phosphorus (P), relative to an arbuscular mycorrhizal fungus Funneliformis mosseae. After 20 weeks, roots of trifoliate orange could be colonized by P. indica, and both P. indica and F. mosseae existed in roots together. Root fungal colonization and soil easily extractable, difficultly extractable, and total glomalin-related protein concentrations were higher under single F. mosseae inoculation than under single P. indica and dual inoculation of F. mosseae and P. indica. Single or dual microbial inoculant collectively improved plant growth including plant height, leaf number, and leaf, stem, and root biomass, compared with non-inoculation. In addition, single fungal treatment raised the content of root N, P, and Mg, and dual inoculation increased only Mg and B contents. The improvement of P by single microbial inoculant was associated with the fungi-accelerated soil phosphatase activity and the fungi-induced root phosphate transporter genes (PT3, PT5, and PT6) expression levels. The positive effects on growth and nutrients were more significant under single F. mosseae than under single P. indica and dual inoculations. It concluded that P. indica has the stimulated roles in plant growth and P acquisition of trifoliate orange, and thus has more applied potentiality in citriculture than AMF as a biofertilizer.