DNA fingerprinting probe specific to isolates of Rhizoctonia solani AG-3

Anastomosis group 3 (AG-3) isolates of Rhizoctonia solani that cause black scurf were recovered from diseased potatoes in Virginia and Lenswood in South Australia. A highly repeated and specific DNA fingerprinting probe, pR3718, prepared from AG-3 isolate R37, hybridized to Southern blots of all AG-3 isolates tested, but had no or very weak reactions with isolates from other anastomosis groups. Genetic variation among the isolates was observed using the fingerprinting probe. Sac I or Hind 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 sequence with a high number of copies per genome and appears to be specific for AG-3 isolates of Rhizoctonia, it has the potential to be used as a diagnostic tool to study the epidemiology, genetic diversity and population dynamics of this important plant pathogen.