Skip to main content
ARS Home » Pacific West Area » Logan, Utah » Poisonous Plant Research » Research » Publications at this Location » Publication #358179
Title: Evidence of non-pathogenic relationship of Alternaria section Undifilum endophytes within three host locoweed plant species

Author
item NOOR, AZIZA - New Mexico State University
item NAVA, AMY - New Mexico State University
item COOKE, PETER - New Mexico State University
item Cook, Daniel
item CREAMER, REBECCA - New Mexico State University

Submitted to: Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2017
Publication Date: 1/4/2018
Citation: Noor, A.I., Nava, A., Cooke, P., Cook, D., Creamer, R. 2018. Evidence of non-pathogenic relationship of Alternaria section Undifilum endophytes within three host locoweed plant species. Botany. 96(3):187–200. https://doi.org/10.1139/cjb-2017-0117.
DOI: https://doi.org/10.1139/cjb-2017-0117

Interpretive Summary: Locoweeds are legumes of the Astragalus and Oxytropis genera that live symbiotically with the fungal endosymbionts belonging to Alternaria section Undifilum. These endophytes produce the toxin swainsonine that causes a neurological syndrome (locosim) when the plant is ingested by grazing animals. Here we characterize the growth of the endophytes within plant tissues using confocal and scanning electron microscopy (SEM) to define the physical relationship. Microscopy results reveal the endophyte distribution to be densely networked, with the mycelia aligned parallel to the long axis of the plant stem and with no pathology to plant cell walls, xylem or phloem. The autofluorescent mycelia were located intercellulary in the pith of stems. Stereofluoroscope observations of Alternaria oxytropis, A. cinerea, and A. fulva in phytoagar showed that mycelial growth occurred at the tip of hyphae. The growth rate of A. cinerea was significantly faster than for A. oxytropis or A. fulva. All three species of endophytes grew significantly faster at 3 days age of culture and grew slowly or not at all at 20 or 30 days. Analysis of the growth of these fungi support the hypothesis that there is a non-pathogenic symbiosis between the fungal endophytes and their host plants.

Technical Abstract: Locoweeds are legumes of the Astragalus and Oxytropis genera that live symbiotically with the fungal endosymbionts belonging to Alternaria section Undifilum. These endophytes produce the toxin swainsonine that causes a neurological syndrome (locosim) when the plant is ingested by grazing animals. Here we characterize the growth of the endophytes within plant tissues using confocal and scanning electron microscopy (SEM) to define the physical relationship. Microscopy results reveal the endophyte distribution to be densely networked, with the mycelia aligned parallel to the long axis of the plant stem and with no pathology to plant cell walls, xylem or phloem. The autofluorescent mycelia were located intercellulary in the pith of stems. Stereofluoroscope observations of Alternaria oxytropis, A. cinerea, and A. fulva in phytoagar showed that mycelial growth occurred at the tip of hyphae. The growth rate of A. cinerea was significantly faster than for A. oxytropis or A. fulva. All three species of endophytes grew significantly faster at 3 days age of culture and grew slowly or not at all at 20 or 30 days. Analysis of the growth of these fungi support the hypothesis that there is a non-pathogenic symbiosis between the fungal endophytes and their host plants.