Three New Species and a New Record of Arbuscular Mycorrhizal Fungi of the Genus Acaulospora Associated with Citrus from South China.

Arbuscular mycorrhizal (AM) fungi are root symbionts that play an important role in the growth of vascular plants. Four AM fungi, including three new species, Acaulospora citrusnsis, A. guangxiensis, A. jiangxiensis, and a new country record from China, Acaulospora herrerae, are reported based on morphological characteristics and molecular phylogenetic analysis. They were isolated and propagated from spores extracted from the rhizosphere soils of citrus. A. citrusnsis is characterized by forming hyaline to pale yellow globose to subglobose spores of (70.0-)85.0(-100.0) μm in diameter. Spores of A. guangxiensis are pale yellow to pale yellowish brown, with spherical to sub-spherical appearance and (103.1-)122.1(-147.1) μm in diameter. Young spores of A. jiangxiensis are hyaline, gradually turning pale yellow as they mature, with spherical to sub-spherical appearance and (78.7-)85.6(-90.0) μm in diameter. Spores of A. herrerae are hyaline and 86.3-127.2 μm in diameter. Four species have three spore wall layers, and spores form individually in the soil. The phylogenetic tree was constructed and inferred from sequences of 18S-ITS1-5.8S-ITS2-28S datasets by Bayesian inference and maximum likelihood analysis. Voucher specimens are deposited in the Center for Subtropical Arbuscular Mycorrhizal Fungi Culture Collection (CSMC).