Exotic Brome-Grasses in Arid and Semiarid Ecosystems of the Western US

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infl orescences. These infl orescences abort because disease development at the base
of the plant apparently blocks the vascular tissue and causes water stress in the
fl owering shoots, in a manner similar to a vascular wilt disease. If surface-sterilized
stem bases of diseased plants are incubated in the laboratory, the irregularly shaped
black stromata characteristic of the family Rutstroemiaceae are produced within the

a

b

Fig. 7.5 ( a ) A patch of Bromus tectorum monoculture that suffered epidemic disease caused by
the bleach blonde pathogen (Rutstroemiaceae sp. n.). Inset shows a close-up of a sterile infl ores-
cence from a diseased plant and a comparison of a sterile fl oret ( left ) with a normal fi lled fl oret
( right ). ( b ) Effect of disease caused by the bleach blonde pathogen on whole plant biomass, num-
ber of fl orets per tiller, and mean mass per fl oret in a greenhouse pathogenicity test. (Florets with
a mean mass of <1.5 mg are nonviable)

7 Community Ecology of Fungal Pathogens on Bromus tectorum