Evaluation of Phytopathogenic Effect of Pectobacterium carotovorum subsp. carotovorum isolated from Symptomless Potato Tuber and Soil

Aims: The comparison of the four combination method to detect and isolate the Pectobacterium spp by using or not the step enrichment and evaluation the effect of the bacterial concentration and assessment date to symptoms expression on the infected plant potatoes.
Place and Duration of Study: Laboratory Virology Hygiene and Microbiology, department Biology, Faculty of Sciences and Techniques, University Hassan-II Mohammedia Casablanca.
Methodology: One hundred fifty samples were collected from symptomless tubers and twenty eight soil samples from the target field. Four combination procedures were performed with or without step enrichement by using DPEM and DIECA to detect and isolate Pectobacterium. The strains were isolated in the CVP (Cristal Violet Pectate) medium after enrichement step with DPEM. The strains S603TM3, S603TM5,P603A1, P303AH2, P303T1, P303K2, P303K4, P303MN2, P603GH2 were identified by biochemical and pathogenecity tests, the confirmation species was performed by PCR using primers Y1 and Y2. During this study, one strain was choice to evaluate the capacity of the Pectobacterium to develop symptoms non–emergence (NE) symptomless plant (SP), chlorosis (Chl); blackleg (Blg); desiccation (Dst).under the following conditions: the combination between the assement date (40 and 70 days) and bacterial concentration ( 104and 108 CFU/ml).
Results: The isolates were performed on medium Crystal Violet Pectate. Their biochemical tests allowed us to conclude that all the isolates belonged to the Pectobacterium. The strains were able to develop the soft rot in the slices of potato, confirmed by PCR yielded an amplified fragment of the size (434 bp). The results of the combination test to detect the Pectobacterium revealed that the enrichment step was.the most efficient technique for Pectobacterium sp isolation comparing to direct plating on CVP medium, 23% of strains were isolated by enriched medium DPEM as compared without enrichment step 13%, detection of Pectobacterium sp was improved by adding Sodium Diethyldithiocarbamate (DIECA). The results of the combination conditions assessment date and bacterial concentration show no effect between the concentration 104 and 108 CFU/ml to develop the symptoms, in the otherwise, chlorosis and blackleg symptoms attenuated and increased after 70 days, the desiccation symptom was also significantly affected by an assessment date.
Conclusion: The detection and isolation of Pectobacterium from asymptomatic potato tubers were improve by enrichement step. Some of these strains were belong to Pectobacterium carotovorum subsp. carotovorum. The development and expression symptom (no emergence, chlorosis, blackleg and dessication) of Pectobacterium in the potato plant is not correlated with assessment date and inoculums level. Otherwise, some physiological and environemental conditions can affect their development.