Impact of Good Seed and Plant Practices on the Incidence of Bacterial Canker in a Commercial Tomato Nursery

W. Chuis, N. Amkraz, E. Boudyach, A. Aoumar and H. Boubaker

Background and Objective: In tomato commercial nursery, Clavibacter michiganensis subsp. michiganensis, the causal agent of bacterial canker, is mainly transmitted by infected seeds and seedlings, so, microbiological analysis of seedlings to prevent the dissemination of contaminated transplants is crucial in bacterial canker management. The purpose of this study was to evaluate the impact of Good Seed and Plant Practices (GSPP) on the incidence of bacterial canker in grafted tomato seedlings produced in a commercial nursery. Materials and Methods: During the 3 years of study (2018, 2019 and 2020), the detection of Clavibacter michiganensis subsp. michiganensis in tomato-seedlings samples was done by dilution plating of stem extract on different culture media. To confirm the molecular identity of the pathogen, one bacterial isolate from each suspected sample was tested by PCR using the primers RZ-ptssk 10 and RZ-ptssk 11. After the PCR analysis, each suspected bacterial isolate was further tested for its pathogenicity by using the cotyledons test on tomato seedlings. Results: During the 3 years, more than one thousand tomato seedlings samples were analyzed for Clavibacter michiganensis subsp. michiganensis contamination and only fifteen samples were identified positive for this bacterial pathogen by using culture isolation on non-selective and semi-selective media. Of these, only four bacterial isolates were positive by using the PCR technique. However, pathogenicity was not confirmed in cotyledon inoculation tests for the four suspected isolates obtained from tomato seedling samples. Conclusion: This study demonstrated that the rigorous application of good seed and plant practices standards and implementation of strict sanitary measures significantly reduce the risk of contamination of grafted tomato seedlings by Clavibacter michiganensis subsp. michiganensis in a commercial tomato nursery.

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