Effects of field inoculation with arbuscular mycorrhizal fungi and endophytic fungi on fruit quality and soil properties of Newhall navel orange

Beneficial fungi - including difficult - to - culture arbuscular mycorrhizal fungi (AMF) and the culturable endophytic fungus Piriformospora indica - play positive roles in hosts under controlled conditions, whereas information regarding the application of these fungi in field citrus (a mycorrhizal - dependent plant) is scarce. The present study aims to analyze the effects of two AMF species (Diversispora spurca and D. versiformis) and an endophytic fungus (P. indica) on the fruit quality and soil properties of Newhall navel oranges (Citrus sinensis Osbeck cv. Newhall) grafted on trifoliate oranges in the field. The results showed the improvement of root fungal colonization following fungal inoculation. The fungal inoculations increased the soil's acid, neutral, alkaline, and total phosphatase activity, as well as soil Bray-P content; increased the distribution of water-stable aggregates, mainly in the size range of 2–4 mm; and stimulated the production of easily extractable, difficultly extractable, and total glomalin-related soil proteins in a fungal-species-dependent manner, which was positively correlated with soil aggregate stability. Fungal inoculations, to some extent, improved external fruit quality, depending on the fungal species. Among the three fungi, only D. versiformis significantly increased the fruits' soluble solid content, but all three together promoted fruit glucose, fructose, and sucrose content. The two AMF species dramatically increased fruit phosphorus (P) content, while P. indica distinctly reduced it. D. versiformis also significantly elevated fruit potassium (K), magnesium (Mg), and manganese (Mn) content, D. spurca improved fruit copper (Cu), zinc (Zn), K, and Mg content, and P. indica increased fruit iron (Fe) and Zn content, compared with non-inoculated controls. Our results indicate that the field inoculation of citrus with AMF and P. indica partially improved fruit quality and soil properties, providing a pathway for P. indica to partially replace AMF in field citrus applications.