Abstract:
Twenty isolates of Erwinia carotovora subspecies atroseptica (Eca) causing blackleg of potato, were collected from tubers and diseased stems of potato plants grown in both plains and mountains of the North-Western Pakistan. The isolates were identified as Eca by biochemical tests and their identity was further confirmed by polymerase chain reaction (PCR) using subspecies-specific primers Eca 1F and Eca 2R which amplified the Eca-specific band of 690 bp. Pathogenicity test divided these 20 isolates into 4 aggressiveness groups or AGs. AG 1 (7 isolates) was the most aggressive group causing an average of 5.69 cm rot on potato stem. AG 2 (4 isolates) and AG 3 (5 isolates) were moderately aggressive producing potato stem rot of 4.93 cm and 4.49 cm, respectively. AG 4 (4 isolates) was the least aggressive, causing stem rot of 3.98 cm only. These isolates were also characterized using the technique of random amplified polymorphic DNA (RAPD). The Unweighted Pair-Group Method using Averages (UPGMA) analysis of the bi-variate data obtained as a result of RAPD,
divided the isolates into four well-defined clusters showing a considerable level of genetic diversity. However, these clusters were not specific to AGs, origin or particular potato variety. Isolates with different aggressiveness levels, originated from plains or mountains and cultured from different potato varieties shared the same clusters. This means that the isolates probably derived from the same source population and got dispersed from one area to another through their hosts.
