Scientific Opinion on the pest categorisation of Clavibacter michiganensis subsp. michiganensis (Smith) Davis et al.

Abstract

The European Commission requested the EFSA Panel on Plant Health to perform the pest categorisation for Clavibacter michiganensis subsp. michiganensis (Cmm). The agent responsible for vascular tomato wilt and canker is the clearly defined and valid gram‐positive taxon C. michiganensis subsp. michiganensis. This pathogen can be accurately identified based on a range of sensitive and specific methods. Tomato (Solanum lycopersicum) is the main host, but peppers (Capsicum annum and C. frutescens) are also naturally susceptible to Cmm. These host plants are cultivated throughout Europe and conditions are conducive to disease development in open fields in southern Europe and in greenhouses. The disease is present in many EU Member States. Outbreaks are rare but usually severe. It causes a range of symptoms on the aerial parts of plants, including the fruits. Detection methods are available for any type of plant material either presenting symptoms or symptomless. Seed testing has proven to be a good control option by discarding contaminated seed lots. Despite tomato seed production being done under strict sanitation using recommended practices, seed contamination still occurs occasionally. Contaminated seeds and transplants are responsible for long‐distance dissemination of the pathogen. Under conducive conditions, even low levels of seed contamination can result in disease outbreaks. Cultivation practices can favour secondary spread of the bacterium and an increase in disease incidence both in greenhouse and in open‐field crops. No effective biological or chemical control agents are registered for bacterial canker in Europe. Cmm meets all criteria defined in International Standard for Phytosanitary Measures (ISPM) 21. Cmm meets all ISPM 11 criteria, although it has been observed in 16 EU Member States. The outbreaks are usually severe but sporadic.

Tomato and Pepper Seeds as Pathways for the Dissemination of Phytopathogenic Bacteria: A Constant Challenge for the Seed Industry and the Sustainability of Crop Production

“…Tomato seed contamination by Cmm may occur systemically, through the vascular tissue, or by its penetration through fruit lenticels and stomata. Then, being the bacterium highly tolerant to desiccation, it can survive on/in seeds for years [37].…”

“…Seeds are a recognised and very efficient pathway for the introduction and dissemination of several pests and pathogens [83] and this is particularly true for tomato seeds, as the most important vegetable crop [84]. Therefore, to ensure their phytosanitary quality and allow their safe trade worldwide, seeds should be treated (or disinfected or sanitised) to reduce the presence of pathogens to a minimum [37]. An excellent example of hygiene in tomato seed production and pathogen control of Cmm is published by the international business chain system, Good Seed and Plant Practices (GSPP), to prevent tomato seeds being infected by Cmm [85].…”

Tomato and Pepper Seeds as Pathways for the Dissemination of Phytopathogenic Bacteria: A Constant Challenge for the Seed Industry and the Sustainability of Crop Production

“…Alternatively, Cmm entry through fruit stomata causes the development of circular lesions in the exo-and mesocarp where the bacteria multiply; such bacteria may then reach the seeds through the endocarp or the locular cavity when the tomatoes ripen, thus infecting the seed testa [43]. The bacterium is highly tolerant to desiccation and can survive on/in seeds for years [44].…”

“…Seed is a recognised and very efficient pathway for the introduction and dissemination of several pests and pathogens [110] and this is particularly true for tomato, as the most important vegetable [111]. Therefore, to ensure their phytosanitary quality and allow their safe trade worldwide, seeds should be treated (or disinfected or sanitised) to reduce the presence of pathogens to a minimum [44]. An excellent example of hygiene in tomato seed production and pathogen control of Cmm is published by the international business chain system, GSPP, to prevent tomato seed to be infected by Cmm GSPP [112].…”

Antibacterial Activity of Essential Oils and Trametes versicolor Extract against Clavibacter michiganensis subsp. michiganensis and Ralstonia solanacearum for Seed Treatment and Development of a Rapid In Vivo Assay

“…Latently infected young plants or asymptomatic infections during late stages of plant development, resulting in the production of contaminated seeds, are also considered important for disease spread [7][8][9]. Prevention, based on seed testing and maintaining pathogen-free seeds and transplants, is currently the most appropriate approach for disease control, and cultural practices such as eradication of infected plants and disinfestation of materials are recommended [2,7,10]. Zero tolerance import and export restrictions have been implemented for Cmm in the European Union with the Commission Implementing Regulation (EU) 2019/2072 of 28 November 2019.…”