Resistance response to Clavibacter michiganensis subsp. michiganensis in different available tomato cultivars in Iran

Tomato bacterial canker caused by Clavibacter michiganensis subsp. michiganensis (Cmm) is a destructive tomato disease in the world and Iran, which can seriously affect the quality of the product. An integrated management program using pathogen-free seeds and resistant cultivars is necessary for disease control. In this study, the reaction of 24 cultivars of tomato was assessed against the disease under greenhouse conditions. Inoculation of seedlings at the 4-5 leaf stage was carried out by injecting a bacterial suspension of 1 × 104 CFU ml-1 at the axil, where the petiole meets the stem. The response of cultivars to the disease was evaluated via three indices, including the time of disease onset, disease severity (DS), and the area under the disease progress curve (AUDPC). The results indicated that AUDPC positively correlated with the time of disease onset (r = 0.85) and disease severity (r = 0.86). Based on the current findings, applying different indexes in response of tomato cultivars to bacterial canker disease provides accurate information about host resistance. The AUDPC index is the most reliable as it has a high positive correlation coefficient with two other indexes. In this study, cultivars ‘Rio Grenade’, ‘King Stone’, ‘Early Urbana Y’, ‘CalJ N3’, and ‘Hyb. Firenze’ showed more resistance against the disease than other studied cultivars. Usage of the mentioned cultivars is recommended in the integrated management program of tomato bacterial canker disease.