PubMed · 14518372
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Dieter Neumann. 2003. Silicon in plants.. https://doi.org/10.1007/978-3-642-55486-5_6
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Asexual, seedborne endophytic fungi in perennial grasses are often viewed as strong mutualists because fitness of the symbiont and host grass are closely coupled. However, at least for some native grasses, the asexual endophyte, Neotyphodium, acts parasitically, yet remains at high frequencies in natural populations. Most previous studies of Neotyphodium effects on host survival have been short term relative to the long life span of the perennial grass host. We therefore tested the hypothesis that Neotyphodium alters the survival in various life stages and long-term survival of adult native Arizona fescue (Festuca arizonica). To test the former, we planted 40 infected (E+) and 40 uninfected (E-, endophyte removed) seeds from four different maternal plants in the field under ambient conditions. We followed survival of seeds, seedlings, and adult plants over a 5-year period. To test the latter, we determined the infection of 1633 adult plants and followed their survival over the next 5-7 years. E+ seeds did not differ from uninfected seeds in terms of overall survival from seed germination to seedling to adult. However, the shape of the survival curve differed, with E+ plants showing higher mortality in early life stages. E+ adult plants did not differ from E- plants in long-term survival. Survival was generally very high during the study, which included a severe and prolonged drought. Infection by asexual Neotyphodium does not increase survival in early life stages or that of adult plants. Because asexual, vertically transmitted symbionts are predicted by evolutionary theory to be strong mutualists, the persistence of high infection frequencies in natural populations without long-term benefits to the host remains enigmatic. One possible explanation is that the long life span of the perennial host and low seedling recruitment may obscure either the costs or benefits of endophyte infection.
Laboratory screening studies were conducted to evaluate the allelopathic potential of fine leaf fescues. Of the seven accessions selected from prior field evaluations for weed-suppressive ability, all inhibited root growth of large crabgrass and curly cress in laboratory assays. Grown in agar as a growth medium and in the presence of living fescue seedlings for 14 or 21 days, test species were sensitive depending on the fescue cultivars. Growth inhibition increased when fescue was grown for increasing periods of time in agar. Seedling fescues produced significant quantities of bioactive root exudates, which were released into the agar medium. Bioactive root exudates were extracted from living fescue roots by using methylene chloride. Shoot tissue was extracted in water and the aqueous extract was partitioned against hexane, ethyl acetate, and methylene chloride. Extracts were tested for inhibitory activity on seedling growth as measured by inhibition of curly cress germination and radicle elongation. Root exudates were more toxic (70% inhibition) than shoot extracts (up 40% inhibition), when formulated at 0.25 mg/ml concentration. Light microscopy and transmission electron microscopy were utilized in an attempt to identify the cellular location of production of secondary products contained in bioactive root exudates. Ultrastructural analysis indicated that the exudate is produced in actively dividing tips of fibrous root cells. The mode of release of these exudates into the environment remains unknown.
Growth of a filamentous fungus endophyte, Neotyphodium, and its host plant, tall fescue, Festuca arundinacea, was examined during the seed germination process under pseudo-microgravity [correction of micrgravity] generated by three dimensional (3D-) clinorotation. The shoot growth of tall fescue infected with the endophyte was remarkably suppressed on a 3D-clinostat compared with that of the ground control. Without being infected, shoot growth of tall fescue was not strongly affected by the 3D-clinorotation. Many aggregated hyphae were observed in the plant seed incubated for 1-day on the 3D-clinostat [correction of clinost] than in those kept on the ground. These results indicate that the clinorotation induces responses in the endophyte and its host plant different from those under normal gravity.