Pity the stinking yew

image indicating the health of normal (top) and diseased (bottom) leaves of Torreya taxifolia (the Florida torreya or stinking yew), an endangered conifer endemic to Florida and Georgia. A close relative of the torreya, the Pacific yew Taxus brevifolia, produces the potent anti-cancer drug taxol — so the torreya's rapid decline to the scant 1 500 trees alive today is of even greater concern than usual for the loss of a species. A fungus, Pestalotiopsis microspora, has recently been found to be associated with around 90 % of the remaining torreyas, in both healthy trees and those showing disease symptoms such as canker and needle spots. Infection of greenhouse-grown torreyas leads to the development of disease symptoms seen in the wild; the diseased leaves shown here are from a plant inoculated with the fungus. The image was obtained using an imaging fluorometer specially designed to assess the photosynthetic function of the plant: dark red/magenta corresponds to the highest quantum yield (healthiest tissue), and dark blue/green to the lowest (least healthy tissue). The damage caused to the torreya is likely to be due to fungal metabolites. Three toxic compounds can be isolated from fungal cultures and two of these can also be isolated from infected plant tissue: all three are toxic to the torreya, and one, pestaloside, is also toxic to various species of fungus. Pestaloside may kill off other fungi that could compete with P. microspora for nutrients, allowing it to become the dominant fungal species growing in the torreya. P. microspora may have become a threat to the torreya because of its introduction with non-native pines, or large scale cultivation in the surrounding areas may have soured a previously healthy coexistence.