ABSTRACT
The fossil record indicates that fungal symbionts have been associated with plants since the Ordovician period (approximately 400 million years ago), when plants first became established on land (Pirozynski and Malloch, 1975; Simon et al., 1993; Remy et al., 1994; Redecker et al., 2000). Transitioning from aquatic to terrestrial habitats likely presented plants with new stresses, including periods of desiccation. Because symbiotic fungi are known to confer drought tolerance to plants (Read and Camp, 1986; Bacon, 1993), it has been suggested that fungal symbiosis was involved with or responsible for the establishment of land plants (Pirozynski and Malloch, 1975). Symbiosis was first defined by De Bary in 1879, and since that time, all plants in natural ecosystems have been found to be colonized with fungal and bacterial symbionts. It is clear that individual plants represent symbiotic communities with microorganisms associated in or on tissues below-and aboveground.
