DNA-FINGERPRINTING PROBE SPECIFIC TO ISOLATES OF RHIZOCTONIA-SOLANI AG-3

Anastomosis group 3 (AG-3) isolates of Rhizoctonia solani that cause b lack scurf were recovered from diseased potatoes in Virginia and Lensw ood in South Australia. A highly repeated and specific DNA fingerprint ing probe, pR3718, prepared from AG-3 isolate R37, hybridized to South ern blots of all AG-3 isolates tested, but had no or very weak reactio ns with isolates from other anastomosis groups. Genetic variation amon g the isolates was observed using the fingerprinting probe. Sac I or H ind III restriction endonuclease digests of DNA prepared from 136 AG-3 isolates revealed 38 fingerprint patterns, each containing 12-19 Sac I or Hind III fragments. Because the pR3718 clone recognizes a DNA seq uence with a high number of copies per genome and appears to be specif ic for AG-3 isolates of Rhizoctonia, it has the potential to be used a s a diagnostic tool to study the epidemiology, genetic diversity and p opulation dynamics of this important plant pathogen.