Distribution and Variability of Clavibacter michiganensis subsp michiganensis in Tomatoes from Northern Hill Region of India

Abstract

The objective of this research was to monitor the existence of Clavibacter michiganensis sub sp. michiganensis (Cmm) in tomato growing region in the northern hill region and to assess its cultural, morphological and pathogenic variability. Tomato samples showing symptoms of Cmm infection were collected and the causal agents were isolated from these samples. On the basis of the presence of characteristic symptoms of Cmm infection in tomato, the mean disease incidence and severity of suspected pathogen was found to be 19.57% and 16.11%, respectively in the middle Himalayan region. From a total of 80 tomato plants sampled, 17 bacterial isolates exhibiting similar colony morphology to Cmm were obtained. After the cultural, morphological and pathogenicity tests, 9 isolates were identified as Cmm. The results of this experiment can be a warning sign for all tomato growers in the region especially those involved in seed trade and vegetable export. For all the collected nine Cmm isolates studies on cultural and pathogenic variability were conducted under laboratory and greenhouse conditions. The design used for the experimental studies was completely randomised. Different strains of Cmm exhibited varied cultural and pathogenic variability while the morphological difference amongst the strains was observed to be non-significant, wherein all the ten isolates were of rod-shaped. During studies on cultural variability, most of the bacterial colonies were initially small, (1-4 mm diameter), mucoid and concave with three different pigmentations viz., yellow, pale-white and orange which became glistening with the increase in age. Amongst the nine isolates studied the isolate, Cmm 10 was most virulent leading to complete plant death within 18th day of inoculation.