Fungal diseases of plants, animals, and humans have altered tree population diversity and forest ecosystem dynamics, devastated agricultural crops, triggered global population declines and extinctions in wildlife, and contributed to death and disability in humans. Cryptococcus gattii (C. gattii), a pathogenic fungus that emerged in 1999 on Vancouver Island, British Columbia, Canada, is causing a growing epidemic of human and animal infections and deaths (Galanis and MacDougall, 2010). Since its initial recognition, the pathogen has spread from Vancouver Island to mainland British Columbia and south into the Pacific Northwest of the United States. This fungal pathogen has been associated with 338 confirmed human infections and 40 deaths1 in these regions, which represents the largest documented population of C. gattii infected people in the world (Datta et al., 2009a; Galanis and MacDougall, 2010). Bat white-nose syndrome (WNS) and amphibian chytridiomycosis2 have caused massive population declines and threaten local extinctions of New World bat and amphibian species, respectively (Frick et al., 2010; Skerratt et al., 2007). By 2009, the geographic range of two virulent and highly aggressive strains3 of yellow “stripe” rust—first detected in North America in 2000—expanded to include major wheat-producing areas on five continents, threatening the global wheat supply (Hovmøller et al., 2010). The recent observation that a fungus (Nosema spp.), in combination with a DNA virus, might be associated with “colony collapse” disorder—a disease that has destroyed 20–40 percent of the honeybee colonies in the United States since 2006—underscores the direct and indirect impacts and ecosystem dynamics of fungal diseases in human, plant, and animal communities (Bromenshenk et al., 2010).

Fungal organisms interact with humans, animals, and plants in beneficial as well as pathogenic ways. A dozen fungal diseases are considered “life threatening” to humans. At the same time, human health has benefited immensely from fungal-derived antibiotics, such as penicillin (Blackwell et al., 2009; Buckley, 2008; Casadevall, 2007). Indeed, fungi are indispensible to life on this planet through their ability to break down complex organic matter and recycle essential nutrients back into the environment (Wainwright, 1992).

The fungal kingdom is among the most diverse kingdoms in the Tree of Life (Blackwell, 2011). Yet, fewer than 10 percent of fungal organisms have been formally described (Hawksworth, 1991, 2001). For the purposes of this chapter, the terms fungi, fungal, and fungus are used inclusively to describe all organisms traditionally studied by mycologists—including species that are now excluded from Kingdom Fungi (e.g., Phytophthora spp. which are members of Oomycota) or whose relationship to the fungal kingdom have yet to be determined (e.g., the


1 As of December 2010.

2 In this chapter, we will refer to this disease as amphibian chytridiomycosis and to the associated pathogen (Batrachochytrium dendrobatidis) as Bd.

3Puccinia striiformis Westend. f.sp. tritici Eriksson.

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