Identification and distribution of a fungal endosymbiotic Alternaria species (Alternaria section Undifilum sp.) in Astragalus garbancillo tissues

ABSTRACT

Plants belonging to the genera Astragalus, Oxytropis, Ipomoea, Sida, and Swainsona often contain the toxin swainsonine (SW) produced by an associated fungal symbiont. Consumption of SW-containing plants causes a serious neurological disorder in livestock, which can be fatal. In this study, a fungal endophyte, Alternaria section Undifilum, was identified in Astragalus garbancillo seeds, using polymerase chain reaction (PCR) followed by direct sequencing. In seeds, the SW concentrations were about 4 times higher than in other parts of the plant. Furthermore, microscopic examination demonstrated that the fungus mycelium grows inside the petioles and stems, on the outer surface and inside the mesocarp of the fruit, in the mesotesta and endotesta layers of the seed coat, and inside the endosperm of the seeds. Our results support the notion that the SW-producing fungus is vertically transmitted in the host plant A. garbancillo.

KEYWORDS:

• Astragalus garbancillo
• endosymbiont
• microscopy
• swainsonine
• Undifilum
• vertical transmission

ACKNOWLEDGMENTS

We thank the two anonymous reviewers for their timely suggestions that helped to improve the manuscript.

DISCLOSURE STATEMENT

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was supported by grants from the Secretaría General de Ciencia y Técnica, Universidad Nacional del Nordeste [UNNE; grant no. PI17B007] and by the Agencia Nacional de Promoción Científica y Tecnológica (PICT 2020/01484).