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Molecular Plant Pathology

Genetic Differentiation Between Phaeosphaeria nodorum and P. avenaria Using Restriction Fragment Length Polymorphisms. Peter P. Ueng, U.S. Department of Agriculture, Agricultural Research Service (USDA-ARS), BARC-West, Bldg. 006, Plant Molecular Biology Laboratory, Beltsville, MD 20705; Weidong Chen, Illinois Natural History Survey and Department of Plant Pathology, University of Illinois, 607 East Peabody Drive, Champaign 61820. Phytopathology 84:800-806. Accepted for publication 2 May 1994. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1994. DOI: 10.1094/Phyto-84-800.

Genetic variation among 14 isolates of Phaeosphaeria nodorum and 10 isolates of P. avenaria that originated from diverse geographic locations was assessed by the use of restriction fragment length polymorphisms (RFLPs). Genomic DNAs were digested with the restriction enzyme EcoRI and hybridized with 38 anonymous DNA probes. Twenty of the 38 probes were isolated from P. nodorum, and the other 18 probes were isolated from P. avenaria. Most of the probes hybridized with one or two DNA bands per isolate. Each isolate was assigned a RFLP genotype, which is a combination of the banding patterns with all 38 probes. Isolates of P. nodorum showed a significantly lower degree of genetic variation than the isolates of P. avenaria. There were seven genotypes among the 14 isolates of P. nodorum, whereas each isolate of P. avenaria had a different genotype. In addition, the minimum number of shared alleles was 34 out of a total of 38 RFLP loci among isolates of P. nodorum in pairwise comparisons, and the minimum number of shared alleles was as low as five among isolates of P. avenaria. In cluster analyses based on individual hybridizing bands (total 155 bands), isolates of P. nodorum formed a tight cluster with a minimum similarity value above 0.9. Bootstrap analysis strongly supported the separation of P. nodorum from P. avenaria. Considerable genetic variation was observed among isolates of P. avenaria. Several RFLP alleles were useful for differentiation of P. nodorum from P. avenaria, and some probes were specific for certain isolates. Those isolate-specific probes may be used as natural markers in epidemiological studies.