RAPD PCR for Diagnosis of Phytophthora parasitica var. nicotianae Isolates which Cause Black Shank on Tobacco

Phytophthora parasitica var. nicotianae is the fungal pathotype of tobacco black shank (TBS, Disease severity ³ 2.0). Random ampli®ed polymorphic DNA (RAPD) analysis was used to di€erentiate isolates which cause TBS from those which do not. Greenhouse assays combined with zoospore inoculation were performed to assess the virulence of the fungal isolates, and the results were compared with the RAPD pattern analysis. The RAPD results exhibited total correlation with the virulence assay results. Ampli®cation patterns generated by RAPD reactions were used to generate a phenogram depicting the genetically distinct nature of the cluster de®ned by the TBS isolates. This cluster was exclusive and distinct from P. parasitica var. nicotianae isolates which do not cause TBS. Thus, RAPD proved to be a sensitive and highly reliable method for quickly identi- fying fungal pathotypes which cause TBS.