Correlation of an Endophytic Fungus (Alternaria spp.) with the Presence of Swainsonine in Lambert Locoweed (Oxytropis lambertii)

摘要

Locoweed poisoning is the most widespread poisonous plant problem in the western USA (Kingsbury, 1964; James and Nielsen, 1988). The term 'locoweed' is defined and used as a general name for those Astragalus and Oxytropis species known to contain toxic levels of the trihydroxy indolizidine alkaloid swainsonine (Molyneux and James, 1982). The presence of swainsonine in locoweeds is believed to be the result of secondary plant biosynthesis (Harris et al., 1988a). Swainsonine is also known to be produced by the plant fungal pathogen Rhizoctonia leguminicola (Harris et al., 1988b), often associated with red clover; Metarhizium anisopliae (Hino et al., 1985), a known insect pathogen; and most recently Alternaria sp. nova (Braun, 1999), a new endophytic fungus associated with locoweeds. Braun (1999) isolated A. sp. nova from several Astragalus and Oxytropis species and found a strong relationship between locoweeds and presence of the endophytic fungus. In addition, A. sp. nova was found to produce swainsonine in vitro. From these findings questions are being asked as to the possible correlation between endophyte infection, swainsonine concentration and toxicity of locoweed plants (Molyneux and James, 1991; Braun and Liddell, 1999).