Root-associated fungal microbiota of the perennial sweet sorghum cultivar under field growth

Root-associated fungal microbiota, which inhabit the rhizosphere, rhizoplane and endosphere, have a profound impact on plant growth and development. Sorghum bicolor (L.) Moench, also called broomcorn or sweet sorghum, is a multipurpose crop. The comparison between annual and perennial sweet sorghum cultivars in terms of plant growth, as well as their interactions with belowground fungal microbiota, is still poorly understood, although there has been growing interest in the mutualism between annual sweet sorghum and soil bacteria or bacterial endophytes. In this study, the perennial sweet sorghum cultivar N778 (N778 simply) and its control lines TP213 and TP60 were designed to grow under natural field conditions. Bulk soil, rhizosphere soil and sorghum roots were collected at the blooming and maturity stages, and then the fungal microbiota of those samples were characterized by high-throughput sequencing of the fungal ITS1 amplicon. Our results revealed that the alpha diversity of the fungal microbiota in rhizosphere soil and root samples was significantly different between N778 and the two control lines TP213 and TP60 at the blooming or maturity stage. Moreover, beta diversity in rhizosphere soil of N778 was distinct from those of TP213 and TP60, while beta diversity in root samples of N778 was distinct from those of TP213 but not TP60 by PCoA based on Bray–Curtis and WUF distance metrics. Furthermore, linear discriminant analysis (LDA) and multiple group comparisons revealed that OTU4372, a completely unclassified taxon but with symbiotroph mode, was enriched in sorghum roots, especially in N778 aerial roots at the blooming stage. Our results indicate that Cladosporium and Alternaria, two fungal genera in the rhizosphere soil, may also be dominant indicators of sorghum yield and protein content in addition to Fusarium at the maturity stage and imply that the perennial sweet sorghum N778 can primarily recruit dominant psychrotolerant bacterial taxa but not dominant cold-tolerant fungal taxa into its rhizosphere to support its survival below the freezing point.