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Abstract
A polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was developed to identify and differentiate genotypes of Rhizoctonia solani anastomosis group 3 subgroup PT (AG-3 PT), a fungal pathogen of potato. Polymorphic co-dominant single-locus PCR-RFLP markers were identified after sequencing of clones from a genomic library and digestion with restriction enzymes. Multilocus genotypes were determined by a combination of PCR product and digestion with a specific restriction enzyme for each of seven loci. A sample of 104 isolates from one commercial field in each of five counties in eastern North Carolina was analyzed, and evidence for high levels of gene flow between populations was revealed. When data were clone-corrected and samples pooled into one single North Carolina population, random associations of alleles were found for all loci or pairs of loci, indicating random mating. However, when all genotypes were analyzed, the observed genotypic diversity deviated from panmixia and alleles within and between loci were not randomly associated. These findings support a model of population structure for R. solani AG-3 PT on potato that includes both recombination and clonality.
We thank Dr. H. Corby Kistler (USDA/ARS, Cereal Diseases Lab, St. Paul, Minnesota), Steven Leath, (USDA/ARS, Dept. of Plant Pathology, NCSU), Tim James, and Daniel Snyder (Dept. of Biology, Duke University,). Special thanks for Pamela Puryear (Tobacco Literature Service, NCSU) for locating literature. This research was supported in part with a research assistantship from CNPq (Conselho Nacional deDesenvolvimento Científico e Tecnológico)—Brasília, DF, Brazil (200873/92–8) and with a graduate student fellowship and E.E. Butler travel award from The Mycological Society of America awarded to PC. A leave of absence was also granted to PC by UNESP (Universidade Estadual Paulista “Júlio de Mesquita Filho”), Ilha Solteira, São Paulo, Brazil, for attending the Ph.D. program on Plant Pathology at North Carolina State University. Special thanks to Drs. Ana Maria R. Cassiolato and Marli F. Stradioto Papa for assuming the teaching responsibilities of PC at UNESP during his absence.