Hereditary symbiosis in the grass genus Danthonia

Abstract

SUMM.'\RYHereditary svTnbiosis between the systemic, clavicipitaceous fungus Atkinsonella hypoxylon (Pk.) Diehl and five taxa of eastern North American Danthonia (Poaceae) was investigated by cultural and histological techniques. Many species of Danthonia, including D. alleni (or D. spicata var. alleni), D. compressa, D. epilis. D. scricea, and D. spicata produce both terminal panicles of wind-pollinated florets and obligately se!f-pollinated cleistogamous florets in the lower leaf axils, unlike most grasses. Terminal florets are aborted by infection while the basal florets produce viable, infected seeds (caryopses). The fungus grew out of surface-sterilized cleistogamous seeds and seedlings at high frequency in progenies from infected plants but not from uninfected plants. Infection of seeds from terniinal panicles from apparently healthy plants was tacking in 11 of 13 population samples from all taxa and was infrequent in two other populations. Growth chamber tests indicated that germination rates of infected and uninfected seeds of D. epilis were similar. Microscopic observations of sections of seeds and seedlings revealed that the fungus occurred epiphytically on meristems, in leaf axils, and on leaf primordia. Because infected plants are partially fertile, the fungus may be repeatedly transmitted for many generations via self-fertilized cleistogamous seeds. The basal, and often subterranean, location of cleistogamous seeds may facilitate high infection frequencies in those Danthnnia populations where cleistogamous seedling establishment predominates.

Occurrence of Fungal Endophytes in Species of Wild Triticum

“…Although the role these Neotyphodium and Acremonium endophytes play in Triticum evolution is unknown, their occurrence in indigenous plants may have contributed to the genetic diversity and persistence of the Triticum species. Endophytic fungi have been found to be involved with the evolution, distribution and, phenotypic plasticity of other grasses such as Danthonia (Clay, 1994), Festuca (Leuchtmann, 1994), and Lolium (Cheplick, 1997) However, a close association between the nonpathogenic, seedborne, fungal endophytes and their hosts does not necessarily imply coevolution between the fungus and host. Evidence within Festuca suggests that the mutualistic, symbiotic relationship between the host and Neotyphodium species may have occurred quite late in Festuca speciation (Schardl and Siegel, 1993)…”

Drivers of grass endophyte communities in prairies of the Pacific Northwest, USA

“…We suspect that Neotyphodium and related clavicipitalean endophytes are more common in our host species than this study suggests because they are often highly localized in plant tissue such as leaf axils, stems, and meristems. They are rarely found in leaf tissue (which we sampled here), and their frequency can depend on season and age of the leaf (Clay 1994, Schardl et al 2004.…”

Genomes of Plant-Associated Clavicipitaceae

“…In most cases, even the ovary and eventually the embryo are infected but undamaged, leading to vertical transmission. Among the Clavicipitaceae, this heritability is known only for Epichloe¨and Periglandula species and for Atkinsonella hypoxylon (Clay, 1994). It seems somewhat ironic, then, that sexual Epichloe¨species fruit on immature host inflorescences and arrest their development, thereby preventing seed production from the symptomatic tillers.…”