Transmission of the locoweed endophyte to the next generation of plants

Authors: Ralphs, Michael; Cook, Daniel; Gardner, Dale; Grum, Daniel

Submitted to: Fungal Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/17/2010
Publication Date: 8/1/2011
Citation: Ralphs, M.H., Cook, D., Gardner, D.R., Grum, D.S. 2011. Transmission of the locoweed endophyte to the next generation of plants. Fungal Ecology. 4(4):251-5.

Interpretive Summary: A fungal endophyte in locoweeds produces the toxic alkaloid swainsonine. The objective of this study was to determine if the fungus is passed to succeeding generations in seed. The endophyte was successfully transmitted and actively colonized 85% of seedlings from parent plants in which the endophyte was cultured. It was present in the remaining 15% of seedlings, but did not grow and colonize them. In a small number of parent plants, the endophyte could not be cultured, though its presence was detected by PCR. The endophyte did not colonize the new seedlings from these plants, and swainsonine was not detected. There appears to be some mechanism by which the endophyte is suppressed or the fungus does not grow. Further research is necessary to determine why and how it is suppressed.

Technical Abstract: 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.