During visiting different greenhouses in Mahalat (Markazi province, Iran) in 2012-2013, bacterial soft rot symptoms were observed on Opuntia and Haworthia spp. These consisted of small brown to black water-soaked lesions that increased in size with time, heavily damaging the affected plants. After evaluation of the pectolytic activity on a medium containing polygalacturonic acid using two indicators, 17 bacterial isolates were selected and identified as Pectobacterium carotovorum subsp. carotovorum based on phenotypic features and specific PCR amplification using two sets of primers. All tested isolates were pathogenic and caused the same type of symptoms upon artificial inoculation. A hypersensitive reaction was induced in tobacco leaves infiltrated with bacterial suspensions. In a phylogenetic tree constructed with sequences of the housekeeping genes recA and pmrA based on individual and combined data sets the Iranian isolates clustered together with Pc subsp. carotovorum ATCC15713, in two subgroups with high statistical support. Those from Opuntia sp. were in the same cluster separated from the Haworthia strains by strong bootstrap values, indicating that the two selected genes could identify Pectobacterium at the subspecies level and monitor the diversity of Pcc subspecies.

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