Prevalence of (Clavibacter michiganensis subsp. Michiganensis) Causal Organism of Bacterial Canker in Weed Species in Tomato Fields of North West Pakistan

Bacterial canker is becoming one of the serious pests in vegetables in Northwest Pakistan. We investigated primary sources of inoculum for bacterial canker of tomato (BCT) caused by Clavibacter michiganensis subsp. michiganensis (Cmm), in a set of 20 weeds commonly found in tomato fields of major tomato growing areas of Khyber Pakhtunkhwa (KP) province, Northwest Pakistan. Based on agroclimate, KP was divided into five zones as Northern KP, Southern KP, Eastern KP, Western KP and Central KP. A total of 100 collected weed samples were analyzed in laboratory for the presence of bacteria. The samples were crushed homogenized in 0.85% TBE buffer and platted on YDC (Yeast extract-Dextrose-CaCO3) for bacterial growth. For identification of the characteristic bacterial colonies Cmm-specific primers CMM-5 and CMM-6 were used for amplification of 614bp product from pat-1 gene of bacterial plasmid. The whole bacterial DNA was used as template, extracted with standard procedures using commercially available kit i.e. protinase-K (sigma). 27 out of 34 isolates were confirmed as Cmm having 614bp band. Black nightshade (Solanum nigrum L) was the only weed from which pathogen was consistently isolated. From Northern KP, a total of nine weeds including; Solanum nigrum L., Solanum americanum Mill., Solanum Sarrachoides Sedntner, Amaranthus blitoides S. Wats, Amaranthus albus L., Lactuca serriola L., Amaranthus retroflexus L., Malva parviflora L. and Sisymbrium irio L.were found to be possible sources of primary inoculum of the pathogen in tomato fields.