Morphological and phylogenetic characterization of Alternaria section undifilum fungal endophytes from Astragalus and Swainsona spp

Authors: NEYAZ, MARWA - New Mexico State University; ADEBISI, OLABISI - New Mexico State University; Cook, Daniel; CREAMER, REBECCA - New Mexico State University

Submitted to: The Journal of Fungi
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/16/2025
Publication Date: 7/19/2025
Citation: Neyaz, M., Adebisi, O., Cook, D., Creamer, R. 2025. Morphological and phylogenetic characterization of Alternaria section undifilum fungal endophytes from Astragalus and Swainsona spp. The Journal of Fungi. 11(7). Article 541. https://doi.org/10.3390/jof11070541.
DOI: https://doi.org/10.3390/jof11070541

Interpretive Summary: The locoweeds Astragalus and Oxytropis in the Americas and China, and Swainsona in Australia harbor Alternaria section Undifilum spp., endophytes that produce swainsonine and induce “loco-ism” or “pea struck” diseases in grazing animals. This study characterizes swainsonine-producing Alternaria species isolated from Astragalus wetherilli, Astragalus pubentissimus, Swainsona canescens, Swainsona galegifolia, Swainsona luteola, and Swainsona brachycarpa. The fungi were isolated from their hosts onto media and expressed slow growth resulted in colonies diameter of 10 mm after 30 days. Morphological identification revealed production of conidia that produced a wavy germ tube for the endophytes from Astragalus pubentissimus species, Swainsona canescens, and Swainsona galegifolia, which is a distinctive feature of Alternaria section Undifilum spp. Sequence analysis of the ITS region and the swnK gene and the swnH2 – swnK intergenic region of these fungi suggest that the fungi isolated from Astragalus are closely related and distinct from the fungi isolated from Swainsona. Fungi isolated from Astragalus spp. differed in color, growth, and conidium size, and/or their se-quences. Fungi isolated from Swainsona canescens and Swainsona galegifolia endophytes differed in color, growth, and conidium size. The endophytes isolated from Swainsona luteola and Swainsona brachycarpa did not produce conidia, and showed similar colony growth rate, and similar sequences. They differed slightly in mycelial diameter and color. Sequence from all Swainsonina endophytes from all three sequenced regions did not vary by more than a single base and were concluded to be the same species. The new species described here are Alternaria wetherum, Alternaria pubentissuin, Alternaria pubentiwy, and Alternaria swainsonum, Characterization of this important group of fungi aids in the understating of their morphology and their association with the host and provide insight into their evolution.

Technical Abstract: The locoweeds Astragalus and Oxytropis in the Americas and China, and Swainsona in Australia harbor Alternaria section Undifilum spp., endophytes that produce swainsonine and induce “loco-ism” or “pea struck” diseases in grazing animals. This study characterizes swainsonine-producing Alternaria species isolated from Astragalus wetherilli, Astragalus pubentissimus, Swainsona canescens, Swainsona galegifolia, Swainsona luteola, and Swainsona brachycarpa. The fungi were isolated from their hosts onto media and expressed slow growth resulted in colonies diameter of 10 mm after 30 days. Morphological identification revealed production of conidia that produced a wavy germ tube for the endophytes from Astragalus pubentissimus species, Swainsona canescens, and Swainsona galegifolia, which is a distinctive feature of Alternaria section Undifilum spp. Sequence analysis of the ITS region and the swnK gene and the swnH2 – swnK intergenic region of these fungi suggest that the fungi isolated from Astragalus are closely related and distinct from the fungi isolated from Swainsona. Fungi isolated from Astragalus spp. differed in color, growth, and conidium size, and/or their se-quences. Fungi isolated from Swainsona canescens and Swainsona galegifolia endophytes differed in color, growth, and conidium size. The endophytes isolated from Swainsona luteola and Swainsona brachycarpa did not produce conidia, and showed similar colony growth rate, and similar sequences. They differed slightly in mycelial diameter and color. Sequence from all Swainsonina endophytes from all three sequenced regions did not vary by more than a single base and were concluded to be the same species. The new species described here are Alternaria wetherum, Alternaria pubentissuin, Alternaria pubentiwy, and Alternaria swainsonum, Characterization of this important group of fungi aids in the understating of their morphology and their association with the host and provide insight into their evolution.