Morrison, Janet .
Spatial and temporal population dynamics of a smut fungus – grass interaction.
Disease dynamics and host population dynamics in natural plant pathosystems remain poorly understood, with only a handful of well-studied systems. We investigated an interaction in which the common perennial old-field grass Andropogon virginicus (broomsedge) is attacked by the parasitic smut fungus Sporisorium ellisii, which replaces the plant’s reproductive structures with its own teliospores. From 2004-2006, in a 100 x 100 m population, we investigated the relationship between host population density and disease frequency by counting infected and healthy plants within 480 permanent 1 m2 plots each year. The effect of disease on individuals was measured on focal plants. Mean plants/m2 ranged from 5.47 in a 2002 pilot study to 3.59 in 2004, 5.52 in 2005, and 3.26 in 2006. Plant density in plots was positively correlated across all pairs of years (all r > 0.64, all P< 0.0001, correlation with CRH correction for spatial autocorrelation). Mean disease frequency in plots ranged from 29.8% in the 2002 pilot study to 10.6% in 2004, 8.9% in 2005, and 5.9% in 2006, and was positively correlated across adjacent years only (2004-2005, P<0.0001; 2005-2006, P = 0.0005). In plots with disease present, disease frequency was negatively correlated with plant density in each year (r = -0.50 in 2004, -0.45 in 2005, -0.63 in 2006; all P < 0.001, with CRH correction). Fully infected plants were smaller than healthy plants, were at significantly higher risk for mortality, and produced no seeds. Although 21.2% of infected individuals recovered from disease, 70% of infected plants died after two years compared to 43% mortality in healthy plants. Sporisorium ellisii has a negative effect on A. virginicus and may act both in population regulation and, potentially, as an agent of natural selection that drives the evolution of A. virginicus populations toward increased resistance.
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1 - The College of New Jersey, Department of Biology, P.O. Box 7718, Ewing, NJ, 08628, USA
Presentation Type: Poster:Posters for Sections
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM