An Epiphytic/Endophytic Fungal Associate of Danthonia spicata Transmitted through the Embryo Sac

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Abstract
A fungal associate of D. spicata (L.) Beauv. is described at the light and electron microscope levels over the life cycle of the host plant. During vegetative growth of the grass, the fungus inhabits the closely ensheathed external surfaces of the shoot apex and ajoining rudimentary leaves, where it produces a microscopic array of fine white filaments around the apex and leaf primordia. With the change of the host to the reproductive phase, the fungus becomes incorporated into the developing ovary and ovule and proliferates between all surfaces, penetrating the micropyle to the megagametophyte wall. During early embryogenesis, hyphae enter the embryo sac and remain there during normal development of the embryo. Invasion of the surface of the embryonic shoot apex occurs before the coleoptile rim encloses it. At germination, hyphae continue to invest the apex of the seedling and so progress into the tillers of the new plant. The fungus functions as both an epiphyte and an endophyte during different phases of the life cycle of the host plant. The fungus, a species of Ephelis, is of sparsely septate, filamentous form, with simple pores and Woronin bodies, indicating an ascomycetous affinity. A thick capsule of apparently mucopolysaccharide composition is a constant component of the hyphal structure in the plant and in culture. Conidia have been observed in culture, but sporulation has not been detected with certainty when the organism is associated with the host plant.

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