Abstract
A total of 100 tomato plant samples exhibiting typical symptoms of bacterial canker were collected from tomato-growing areas of north-western areas of Pakistan. On isolation of the causal agent of this disease, 47 out of 100 samples yielded typical colony morphology of Clavibacter michiganensis subsp. michiganensis, when grown on Nutrient agar (NA) medium. 34 isolates out of the 47 exhibited Clavibacter michiganensis subsp. michiganensis like cultural characteristics when grown on Yeast extract-Dextrose-CaCO3 (YDC) medium. However, 27 isolates only out of these 34 were confirmed to be Gram positive. Pathogenicity of the 27 Clavibacter michiganensis subsp. michiganensis isolates were confirmed using cotyledon, young seedlings and old seedlings assays. Results showed that all these isolates were able to cause bacterial canker disease symptoms on tomato plants. Cotyledon assay was negative for isolates from Mansehra (MNS2); whereas, MNG1 isolate didn't produce any symptoms for all three tests. Old seedlings test was negative for four isolates mainly; MKD2, MNG1, DIK1 and NWS2. To investigate the hypothesis that appearance of symptoms depends on inoculum concentration of pathogen; two aggressive isolates of Clavibacter michiganensis subsp. michiganensis i.e., MKD1 (from Malakand) and KLM1 (from Kalam) were inoculated into tomato plants at different concentrations (i.e. 1×102 - 108 cells/ ml). Results reported that earlier and more severe disease symptoms of bacterial canker were produced by the more aggressive isolate (MKD1); compared to the moderately aggressive isolate (KLM1), which produced milder and delayed disease symptoms on tomato plants.
Highlights
Tomato (Solanum lycopersicum) is grown worldwide for its edible fruits
The current study aimed to evaluate the pathogenicity of Clavibacter michiganensis subsp. michiganensis isolates on three different tomato growth stages; and to find the effect of inoculum concentration on disease severity of bacterial canker of this crop
Surveys conducted in various locations of Khyber Pakhtunkhwa (KP) resulted in the collection of a total of 100 tomato samples showing typical symptoms of bacterial canker such as; bird’s-eye-spot on leaves/ stems or/ and fruits, wilted leaves, tunneling and splitting of stem, retarded growth, and necrosis of leaf margins
Summary
Tomato (Solanum lycopersicum) is grown worldwide for its edible fruits. Due to its high nutritive value; tomato consumption is believed to benefit the heart and reduce cardiovascular diseases (Shidfar et al, 2011). There are about 7500 varieties of tomato which were grown for different purposes (Allen, 2008). Regarding the annual production of tomatoes worldwide; it reached 148.26 million tons (MT) in 2013. Pakistan produced 0.57 MT of tomatoes during 2013 Tomato crop is grown all over the Pakistan, and about 58196 hectares areas were grown with different varieties of this crop. Regarding the average per hectare global production of tomatoes; Belgium and Netherland were on top with 5.0×106 and 4.9×106 kg/ ha; respectively. Pakistan holds 142th position with a much lower average production of 9.8×103 kg/ ha
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