1. Evidence for nonpathogenic relationships of Alternaria section Undifilum endophytes within three host locoweed plant species
- Author
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Noor, Aziza Ibrahim, Nava, Amy, Cooke, Peter, Cook, Daniel, and Creamer, Rebecca
- Subjects
Legumes -- Diseases and pests ,Ascomycota -- Health aspects ,Plant-pathogen relationships -- Observations ,Biological sciences - 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, which 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 revealed 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 after 20 or 30 days. Analyses of the growth of these fungi support the hypothesis that there is a nonpathogenic symbiosis between the fungal endophytes and their host plants. Key words: confocal microscopy, autofluorescent mycelia, hyphal growth, endophyte, locoweeds, symbiosis. Les oxytropsis sont des legumineuses des genres Astragalus et Oxytropis qui vivent en symbiose avec les endosymbiotes fongiques appartenant a Alternaria, section Undifilum. Ces endophytes produisent une toxine, la swainsonine, qui provoque un syndrome neurologique (locoisme) lorsque la plante est ingeree par les animaux de paturage. Les auteurs caracterisent ici la croissance des endophytes a l'interieur des tissus vegetaux a l'aide de la microscopie confocale et la microscopie electronique a balayage (MEB) afin de definir leur relation physique. Les resultats de la microscopie revelent que la distribution de l'endophyte est en reseau dense, les myceliums etant alignes parallelement a l'axe long de la tige de la plante, sans pathologie apparente au niveau des parois cellulaires, du xyleme ou du phloeme de la plante. Les myceliums autofluorescents etaient localises a l'interieur des cellules dans le coeur des tiges. Des observations en stereomicroscopie a fluorescence d'Alternaria oxytropis, A. cinerea et A. fulva sur << Phyto Agar >> montraient que la croissance des myceliums se deroulait a l'extremite des hyphes. Le taux de croissance de A. cinerea etait significativement plus rapide que celui de A. oxytropis ou A. fulva. Les trois especes d'endophytes croissaient significativement plus rapidement a 3 jours de culture et croissaient lentement ou plus du tout a 20 ou 30 jours. L'analyse de la croissance de ces champignons appuie l'hypothese a l'effet qu'il existe une symbiose non pathogene entre les endophytes fongiques et leurs plantes hotes. [Traduit par la Redaction] Mots-cles : microscopie confocale, mycelium autofluorescent, croissance des hyphes, endophytes, oxytropis, symbiose., Introduction Locoweeds are toxic perennial flowering plants of the genera Astragalus and Oxytropis. Astragalus is a very large genus found in many geographic areas including the United States, Canada, South [...]
- Published
- 2018
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