Endogenous fungi isolated from three locoweed species from rangeland in western China

Abstract

Leguminous locoweeds cause toxicosis to grazing animals in western China and western USA. Swainsonine, a toxic alkaloid, is produced by the endophytic fungus Alternaria section Undifilum sp. living within the locoweed plants. Nothing is known of the other endogenous fungi associated with locoweed and it is unknown if the presence of Alternaria sect. Undifilum sp., a potential mutualist, in a locoweed influences the fungal microbiome associated with the plant. To help address these questions, endogenous fungi associated with three locoweed species (Oxytropis glabra, Sphaerophysa salsula, and Astragalus variabilis) collected from grasslands from western China were evaluated. Fungi were isolated from the tissues and identified by morphological features and sequencing of the internal transcribed spacer (ITS) regions. A total of 1209 fungal isolates were obtained from 1819 tissues for an isolation rate of 66.5%. Alternaria sect. Undifilum oxytropis, Alternaria spp. and Fusarium spp. were most commonly isolated. Plant host species, plant part, and environment influenced the endogenous fungal communities isolated from the locoweed plants. There were significant differences in the diversity of fungal species isolated from O. glabra from two sites, and no differences between the diversity of fungi isolated from A. variabilis from two sites. Alternaria sect. Undifilum was found most frequently associated with toxic locoweeds. Plants or plant parts that did not yield this endophyte had more plant pathogenic fungi associated with them. This is the first report of the diversity of fungi associated with these locoweeds and the first to suggest a beneficial role for Undifilum.

Host Genotype and Precipitation Influence of Fungal Endophyte Symbiosis and Mycotoxin Abundance in a Locoweed

“…Sequence alignment of the digested bands suggested those partially digested amplicons represented both the A. oxytropis ITS sequence (Figure S5) and the chloroplast sequence and was, therefore, considered an A. oxytropis -positive plant. In all the 90 samples sequenced, no other Alternaria species were identified despite their high genetic homology to A. oxytropis [35]. Infection rates reflected the number of infected individuals as a proportion of the total number of plants in each accession.…”

Evidence for nonpathogenic relationships ofAlternariasectionUndifilumendophytes within three host locoweed plant species

“…Since locoweeds hosting A. oxytropis do not show any adverse symptoms, the relationship between locoweed and A. oxytropis are non-parasitic and possibly mutualistic similar to the grass/Epichloë system. The Alternaria section Undifilum species may help to prevent other D r a f t pathogenic fungi or microorganisms from plant invasion (Zabalgogeazcoa 2008;Martinuz et al 2012;Lu et al 2017). In addition, the endophyte may prevent other pathogenic infection by utilizing available nutrients and niches.…”

Rethinking of the Roles of Endophyte Symbiosis and Mycotoxin in Oxytropis Plants

“…Undifilum is present in the soil remain unambiguous. Lu et al [21] isolated several fungi from the soil locoweeds grew, and although those fungi produce swainsonine they did not belong to A. sect. Undifilum.…”

“…However, recent studies showed that A. sect. Undifilum might help their locoweed hosts against pathogens [21], or regulate the endophytic fungi assemblage [22]. Therefore, the ecological role of locoweed symbiosis awaits further investigation.…”

“…Endophytes, including A. sect. Undifilum could be successfully cultured from plant leaf material from locoweeds [21]. This strategy can be supplemented by microscopic approaches to observe endophyte in planta.…”