Perennial Infection

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Science  06 Apr 2007:
Vol. 316, Issue 5821, pp. 19
DOI: 10.1126/science.316.5821.19a

Although grazing and fire have been proposed as explanations for the remarkable success of exotic annual grasses in California, where they have established themselves among the native perennials over wide swathes of the landscape despite being inferior competitors for resources, active management based on these factors has failed to stem the invasions. It is known that disease can alter the competitive balance between species in ecological communities, and Borer et al. have developed a model showing quantitatively how invasion has been mediated by viral disease (barley and cereal yellow dwarf viruses, which are a major pathogen in crops, including wheat, barley, and oats). They find that the key to the success of the annual grasses is that virus is horizontally transmitted by aphids, rather than vertically via seeds; hence, seed survival is unaffected, and each generation suffers infection anew. In contrast, perennial grasses serve as long-term reservoirs for the virus and experience deleterious effects on survival and on lifetime seed production, thus facilitating the invasion by annuals. — AMS

Proc. Natl. Acad. Sci. U.S.A. 104, 5473 (2007).

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