Submitted to: Biocontrol Science and Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/30/2006
Publication Date: 12/5/2006
Citation: Caesar, A.J. 2006. Uromyces Scutellatus as a keystone species affecting Euphorbia spp. in Europe as shown by effects on density in the field. Biocontrol Science and Technology. 16:1079-1086. Interpretive Summary: The potential impact of a rust fungus to affect the density of the European forebears of leaf spurge was demonstrated by comparing the relative densities stands of rust-diseased spurge plants with the densities of plants in nearby stands with no or little disease. Densities estimated from measuring the 2-3 of the second and third nearest plants to 10-20 plants exhibiting symptoms of systemic rust (characterized by yellowed, spindly growth) were 48-73% of densities of Euphorb plants estimated from symptomless stands. This study is the first concerning a plant pathogen to fulfill an approach recommended by Wapshere in 1985 that impact of a candidate biocontrol agent species be assessed in its native range.
Technical Abstract: Nearest neighbor spatial analysis was used to assess the effect of systemic rust caused by Uromyces scutellatus on stands density of Euphorbia esula/virgata, a highly invasive deep-rooted perennial weed of rangelands and natural areas in North America. ANOVA applied to nearest neighbor measurements within four pairs of stands in close proximity, with and without rust, in Hungary and Austria indicated that the stand densities of plants of E. esula/virgata in three of four rusted stands were less than companion stands with little or no rust. Using the nearest neighbor distance data, E. esula/virgata densities within stands where rust was prevalent were 48-73% of those with little or no rust. The fourth stand with rust was denser than a symptomless companion stand in 2004, but nearly all plants had symptoms. The same diseased stand was dramatically reduced in density when surveyed the following year and all plants observed in 2005 displayed rust symptoms. These findings indicate the potential impact of the microcyclic autoecious rust U. scutellatus should it be introduced as a biocontrol agent for E. esula/virgata in North America.