Relationship Between the Endophyte Embellisia spp. and the Toxic Alkaloid Swainsonine in Major Locoweed Species (Astragalus and Oxytropis)

Abstract

Locoweeds (Astragalus and Oxytropis spp. that contain the toxic alkaloid swainsonine) cause widespread poisoning of livestock on western rangelands. There are 354 species of Astragalus and 22 species of Oxytropis in the US and Canada. Recently, a fungal endophyte, Embellisia spp., was isolated from Astragalus and Oxytropis spp. and shown to produce swainsonine. We conducted a survey of the major locoweeds from areas where locoweed poisoning has occurred to verify the presence of the endophyte and to relate endophyte infection with swainsonine concentrations. Species found to contain the fungal endophyte and produce substantial amounts of swainsonine were A. wootoni, A. pubentissimus, A. mollissimus, A. lentiginosus, and O. sericea. Astragalus species generally had higher concentrations of swainsonine than Oxytropis. Swainsonine was not detected in A. alpinus, A. cibarius, A. coltonii, A. filipes, or O. campestris. The endophyte could not be cultured from A. mollissimus var. thompsonii or A. amphioxys, but was detected by polymerase chain reaction, and only 30% of these samples contained trace levels of swainsonine. Further research is necessary to determine if the endophyte is able to colonize these and other species of Astragalus and Oxytropis and determine environmental influences on its growth and synthesis of swainsonine.

Selenium Distribution and Speciation in the Hyperaccumulator Astragalus bisulcatus and Associated Ecological Partners

“…Considering the life cycle and host colonization of vertically transmitted fungal endophytes, it is possible that the same endophyte occurs throughout the plant. Systemic endophytic colonization in the apoplast of leaves, stems, and reproductive structures has been documented for several Astragalus species (Ralphs et al, 2008). If this is the case here, it may explain the occurrence of Se 0 in the seedling root, the taproot, and particularly the stem.…”

Plant Bioactive Metabolites and Drugs Produced by Endophytic Fungi of Spermatophyta

“…It has been observed that a fungal endophytic species occurring in locoweeds, the vertically-transmitted Undifilum oxytropis [324,325], previously described as Embellisia sp. [326,327], is capable to produce swainsonine in vitro. Novel species of Undifilum, U. fulvum and U. cinereum, have been later reported for production of this compound, respectively in Astragalus lentiginosus and A. mollissimus [328], along with strains of an unidentified Undifilum sp.…”

Solutions to Locoweed Poisoning in New Mexico and the Western United States: Collaborative research between New Mexico State University and the USDA–Agricultural Research Service Poisonous Plant Lab

“…4 The concentration of swainsonine also varies within a species and within a population of a species. For example, some populations of Lambert locoweed (O. lambertii), and plants within each population of white, woolly, and spotted locoweed, contain very low levels of the endophyte, thereby producing only trace amounts of swainsonine.…”

“…For example, some populations of Lambert locoweed (O. lambertii), and plants within each population of white, woolly, and spotted locoweed, contain very low levels of the endophyte, thereby producing only trace amounts of swainsonine. 4 This suggests that the endophyte must grow and colonize the plant at some critical threshold before swainsonine is produced at toxic levels. Offspring from these plants also had low levels of the endophyte and only traces of swainsonine.…”