Genetic variation among 38 isolates of Stagonospora sp. and 10 isolates of Septoria sp. from bindweed was studied using (a) restriction fragment length plymorphism (RFLP) analysis of the internal transcribed spacer (ITS) region, and (b) random amplified polymorphic DNA (RAPD) PCR analysis RFLP analysis revealed three types of fragment patterns among the isolates A total of 26 distinct groups, based on common fragment patterns, were identified using cluster analysis of the RAPD-PCR data. When the grouping results of the two methods were compared the fragment pattern types and clusters were generally in agreement. The degree of pathogenicity of six genetically characterized isolates of Stagonospora sp. was assessed on three ecotypes of field bindweed (Convolvulus arvensis). Disease symptoms were observed with all isolates on all ecotypes, but only Stagonospora convolvuli strain LA39, a potential biocontrol agent, showed a high degree of pathogenicity on all ecotypes A mixture of two Stagonospora sp. enhanced the mean necrotic leaf area on bindweed from 33.9 and 39.0% (when applied alone) to 64.9% applied together at the same final concentration of 5 x 10(6) spores ml(-1). Molecular methods were used to identify the two pathogens Both were present on the same plant when applied together; but never found in the same lesion.
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