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A TOMATO CANKER. 



By ETHEL M. DOIDGE, 



(Assistant Chief and Senior Research Officer, 

 Division of Botany, Pretoria.) 



(With 5 Text-figures and Plate XXVI.) 



Introduction. 



A disease which may be described as a canker of tomatoes was first 

 noticed in fruit on the Pretoria market during the summer of 1914. 

 It is most prevalent from January to March, and during that period 

 each year (1914-20) a large percentage of the fruit offered for sale 

 was disfigured. Affected fruit rapidly becomes attacked by soft rot 

 organisms which enter the fruit through cracks caused by the scab 

 lesions and destroy it within a few days. 



The incidence of the disease has a direct relation to the rainfall. 

 Tomatoes which ripen in the early summer are seldom attacked, being 

 grown under irrigation, and the disease is seldom observed up to the 

 end of November. From November to January the temperature is 

 high, and there is usually a considerable amount of rain; moist, humid 

 conditions are favourable to the development of the disease. The fruit 

 can only become seriously scabbed when it is attacked by the organism 

 in the early stages of its development; this would account for the non- 

 appearance of the disease before December or January. A few lesions 

 are to be found on fruits as late as June, but the disease can be regarded 

 as serious only during the summer months. 



The occurrence of canker in fruit on the Pretoria market was sug- 

 gestive of the fact that the disease occurred in market gardens in the 

 district; several tomato growers were visited and the surmise found to 

 be correct. Canker is a very common trouble in market and private 

 gardens in the Pretoria district; it is reported to occur also in the 

 Rustenburg district, but I have seen no specimens from there, and 

 beyond this nothing is known of the distribution of the disease. It is 

 not regarded as being of a very serious nature, but a large percentage 

 of the fruit is disfigured, and much of it decays if it is kept for a few 



