Seasonal Variation in Swainsonine and Endophyte Concentrations of Undifilum oxytropis in Different Plant Parts of Oxytropis sericea
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AbstractLocoweeds (Astragalus and Oxytropis spp.) are widely distributed in the rangelands of the western United States. The primary toxin present in locoweeds is identified as the alkaloid swainsonine. The consumption of locoweeds by domesticated cattle, sheep, and horses leads to significant economic losses due to locoism, a neurological disease caused by swainsonine. The fungal-endophyte Undifilum oxytropis, found in locoweed plant species of Astragalus and Oxytropis spp., is thought to be responsible for the synthesis of swainsonine. It has been shown that the swainsonine alkaloid and fungal endophyte are not uniformly distributed within the different parts of Oxytropis sericea. To understand better how swainsonine and endophyte are influenced by the phenology of the plant, both swainsonine and endophyte concentrations were measured in different plant parts (leaf, flower, and crown). These concentrations were determined at five developmental stages (vegetative, early flower, early pod, full pod, and pod shattered) of O. sericea at four different geographic locations. The results showed that the overall swainsonine concentration of O. sericea increased significantly from early flower stage to full pod stage, while endophyte concentration significantly increased from early flower stage to pod shattered stage. There were location× stage× part interactions in swainsonine concentration, but not in endophyte concentration (P < 0.0001 and P = 0.1147, respectively). Swainsonine and endophyte concentrations differed among locations (P < 0.0001 and P < 0.0001, respectively) but did not mirror each other. While endophyte and swainsonine concentrations were correlated (all P < 0.05 except for Harstel, CO), other factors may influence the products of swainsonine in these plants, such as environment, endophyte and plant genotypes.