Ribosomal DNA Restriction Fragment Length Polymorphisms inRhizoctonia solani

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Abstract
Restriction fragment length polymorphisms (RFLPs) in the nuclear encoded ribosomal DNA repeat of the fungal pathogen Rhizoctonia solani revealed considerable molecular variation among and within intraspecific groups that have been recognized previously on the basis of anastomosis, morphology, and pathogenicity. Genomic DNAs from 87 isolates of R. solani were surveyed for RFLPs by digestion with the restriction enzymes EcoRI and BamHI and analyzed by Southern blotting against a ribosomal DNA probe originating from anastomosis group 4. Each of the 15 intraspecific groups of R. solani are characterized by one or more unique RFLPs. Levels of intragroup RFLP variation were within the ranges of RFLP variation of the different anastomosis groups (AGs) and their subgroups. Isolates from anastomosis groups 3, 4, 7, 8, and BI all possess a single, invariant RFLP unique to each intraspecific group. A relatively low level of RFLP variation also was characteristic of isolates within AG-1-IB, AG-1-IC, AG-2-2, and AG-9. In contrast, a relatively high level of RFLP diversity was observed among isolates within AG-1-IA, AG-2-1, AG-5, and AG-6. We did not observed any obvious relationship between levels of RFLP within intraspecific groups and variation of other biological factors (host range, morphological variation, etc.). Instead, we propose that the pattern of RFLP variation observed is most likely the results of genetic diversgence within and among intraspecific groups.