STUDIES ON THE CHARACTERIZATION AND PCR IDENTIFICATION OF THE PATHOGEN OF THE BACTERIAL BLACKLEG/SOFT ROT OF POTATO

In order to get cultures of the causal organisms, large number of potato plants and tuber samples showing symptoms of blackleg/soft rot disease were analyzed in the lab. using nutrient agar (NA) and/or the enrichment host (bell pepper). Successful isolations were made from 44 samples out of these 44 isolates 20 were found to be Erwinia carotovora ssp. atroseptica (Eca) and 24 were identified as either Erwinia carotovora ssp. carotovora (Ecc) or Erwinia chrysanthemi (Ech). The twenty candidate Eca isolates were confirmed by PCR using Eca-specific primers. The key diagnostic tests (such as acid production from α-methyle glucoside, production of reducing substances from sucrose, sensitivity to erythromycin and growth at 36°C) which differentiate between Eca, Ecc and Ech gave inconclusive results in case of some isolates. This situation was successfully clarified by using sub-species-specific PCR primers.