Transmission of the locoweed endophyte to the next generation of plants

Locoweed species of the legume genera Astragalus and Oxytropis (Fabaceae) contain the toxic alkaloid swainsonine, and poison livestock in semi-arid regions throughout the world. Recently, the endophyte Undifilum oxytropis (previously characterized as Embellisia spp.) was found in species of Astragalus and Oxytropis, and was shown to produce swainsonine. A survey of major locoweed species was conducted throughout the western U.S. in 2005 to verify the presence of the endophyte and swainsonine. Seed from these plants was collected to verify the transmission of the endophyte to progeny. In study 1, seed from each parent plant from which the endophyte could be cultured was germinated and seedlings were grown for 4–6 months and then harvested. The presence and quantity of the endophyte was determined by real-time PCR, and swainsonine concentration by LC/MS. The endophyte was transmitted to nearly all of the progeny, however, it was extremely low (<0.38 pg endophyte DNA/ng total DNA) in 15 % of the samples, and swainsonine was near the detection threshold or not detected. In the remaining 85 % of the samples, the endophyte ranged from 3.2 to 36.2 pg ng−1, and swainsonine concentration ranged from 0.21 % to 0.79 %. In study 2, seeds were taken from parent plants in the original 2005 survey from which the endophyte could not be cultured, though its presence was detected by PCR. The seeds were germinated and seedlings were grown for 4 months. The endophyte was detected by PCR in 94 % of the progeny, but the amounts were very low (<0.29 pg ng−1) and swainsonine was not detected in any of the samples. It appears that U. oxytropis has near perfect (approaching 100 %) vertical transmission to the next generation of seedlings. However, a small proportion of the progeny had low endophyte/low or no swainsonine, and this characteristic was inherited in the next generation.