A Tomato Canker, 



719 



as caused by Bacillvs lafJiyri, is characterized, as Uie name suggests, 

 '' by the formation of dark brown or black sunken patches on the 

 stem, varying from small spots to long furrows or blazes." On the 

 fruit it forms lig'ht or dark brown sunken patches, with lound or 

 iiregular outline. 



The effects of the canker organism on leaf stem and fruit are 

 widely different from any of these, as will be evident from the detailed 

 description given later. 



Symptoms of Disease. 



On the lea\es tlie first indication of infection is the appeaiance 



of numerous dark green, semi-translucent, water-soaked points on the 



•under surface. In cases of artificial infection in autumn weather this 



occurred 7-8 days after inoculation ; under summer conditions the 



Tomatoes showing Typical "Cankers." 



progress of the disease may be more rapid. The spots increase in size 

 and become round or irregular, and about 2 mm. in diameter; they 

 are slightly sunken and are often present in such numbers in the 

 neighbourhood of the lateral veins and leaf margins that they coalesce, 

 and produce irregular, discoloured streaks. The colour soon changes 

 from dark green to a purplish grey. The discoloration penetrates to 

 the upper surface, and the spots eventually consist of a smoke-grey 

 centre, which is thin and membranous, and surrounded by a deep 

 brown margin. 



Where the spots are numerous the intervening leaf tissue becomes 

 dry and brown. In this way the affected portions of the leaf, epecially 

 the edges and the tips, become dead and dry, and break away, giving 

 the leaves a very raggy appearance; and many of the smaller leaflets 



