The Relationship of Endophytic Fungi to the Gametophyte of the Fern Schizaea pusilla

Abstract

Schizaea pusilla is a rare and threatened fern restricted in North America to acidic bogs of Nova Scotia, Newfoundland, and New Jersey. The gametophyte lives in close association with two endophytic fungi. To characterize the nature of this fern's relationship with these fungi, we introduced axenic gametophytes to bog soil for colonization. Following colonization, the endophytic fungi were isolated and reintroduced to axenic gametophytes. The gametophytes introduced to bog soil were colonized by an aseptate fungus that formed vesicles and arbuscules within the gametophyte. However, culture of colonized gametophytes produced two fungal isolates: an aseptate fungus (fungus B) and a septate fungus (fungus A). Upon reintroduction of fungal isolates to axenically grown gametophytes, the aseptate fungus demonstrated a positive growth response to the presence of the gametophytes and colonized the gametophytes without harm to the host. The septate fungus did not exhibit any specific recognition but contacted the gametophytes randomly, leaving a large percentage of the host nonviable. We propose that the relationship of the septate fungus to the gametophyte of S. pusilla is nonmycorrhizal while the relationship of the aseptate fungus to the gametophyte is mycorrhizal. Furthermore, based on lack of nutrient availability in local soils, formation of specialized structures in the gametophyte for harboring fungi, and dependence of the fern on fungal presence for completion of its life cycle, we propose that S. pusilla maintains an obligatory relationship with the aseptate mycorrhizal fungus.

Liverworts (Marchantiophyta) of Mahogany Hammock, Everglades National Park, Florida

“…55 temperate A. pusilla has long been cultivated and studied. Britton and Taylor (1901) reported mycorrhizal associations of both the gametophyte and sporophyte stages of A. pusilla, and this association was further described as an obligatory relationship for the gametophyte by Swatzell et al (1996), which was further supported by Merckx and Freudenstein (2010) who reported that the gametophytes of Schizaea (including Actinostachys) are mycoheterotrophic.…”

Fungal associations in gametophytes and young sporophytic roots of the fern Nephrolepis exaltata

“…To our knowledge, the presence of septate endophytic fungal colonization in green fern gametophytes is being reported for the second time. SWATZELL et al (1996) isolated a septate fungus from the gametophytes of Schizaea pusilla. However, the fungus failed to exhibit any specific recognition and rendering 10.3% of the host non-via-…”

Mycorrhizal association in gametophytes and sporophytes of the fern <i>Pteris vittata</i> (Pteridaceae) with <i>Glomus intraradices</i>

“…Previous studies showed that gametophytes of different genera as: Pteridium, Histiopteris, Todea, Cyathea, Asplenium, Blechnum and Schizaea pusilla grown in natural environments were colonized by arbuscular mycorrhiza when they were found in places where nutrients were unavailable (Cooper 1976, Swatzell et al 1996. Although, as it was shown in this study, the development of the symbiosis between the gametophytes and the Glomalean fungi is not obligatory, we observed that the sporophyte was usually colonized by Glomus intraradices, leading to the notion that sporophytes could be colonized by other mycorrhizal fungus.…”