Abundant and diverse fungal microbiota inhabit the white females and brown cysts of the cereal cyst nematode

Cysts of plant-parasitic nematodes containing eggs with secondary-stage juveniles represent entities for long-term survival in soils and serve as an inoculum source for the next cropping season. Fungi are considered to be one of the major factors regulating population densities of cyst nematodes in natural and agricultural ecosystems. However, our understanding regarding the structure of fungal communities colonizing white females and cysts of the cereal cyst nematode (CCN, Heterodera avenae) and information on microbial succession from female to cyst is still limited. Herein, CCN white females attached to wheat roots and mature brown cysts in soil were collected from wheat grown fields at four different locations in central China, and their associated fungal communities were investigated using high-throughput sequencing. The results showed that there were no significant differences in the observed OTUs and Shannon diversity of fungal communities in the white females and cysts across the four locations. However, the mycobiota composition was different between white females and cysts. The phylum Mortierellomycota was more abundant in the white females than in cysts, while Ascomycota had higher relative abundance in the cysts than in white females. An operational taxonomic unit (OTU) enrichment analysis using combined samples for the white females as well as for the cysts from four locations revealed that only a small subset of OTUs were significantly enriched in white females (15 OTUs) and cysts (12 OTUs). These OTUs belonged to genera such as Mortierella, Fusarium, Alternaria, Aphroditeola, Cladosporium, Cryptococcus, Olpidium, Penicillium, Periconia, Volvariella, Phaeosphaeria and Moleospora, and most of them were assigned to functional traits such as endophyte, plant pathogen, animal pathogen, fungal parasite and saprophyte. However, the relative abundances of previously well-documented nematode egg-parasites such as Pochonia chlamydosporia, Purpureocillium lilacinum and other potent taxa were not significantly different between white females and cysts. Our results indicated that white females and cysts harbor diverse mycobiota, and the majority of fungal taxa maintain a steady-state composition from the white females to mature brown cysts.