718 Journal of the Department op Agriculture. 



A TOMATO CANKER. 



By E. M. 1)<)11)(;f., M.A., D.Sc, F.L.S.. Assistani C^hief, 

 Division of Botany. 



Introduction. 



A DISEASE which may he 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 (1914-1920) a large percentage of the fruit offered for sale 

 is disfigured, and 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 irrig-ation, 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 recorded as serious only during the summer 

 months. 



The occurrence of canker in fruit on the Pretoria market was 

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

 the district; several tomato growers were visited and the surmise 

 was found to be correct. Canker is a veiy 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 days after ripening. The siimmer of 1919-20, when 

 most of the observations were made, was exceptionally dry; during 

 another season with heavier or more continuous rainfall the losses 

 would probably be far more serious, and the disease mig-ht ruin the 

 whole crop. 



The "canker" lesions differ from those caused by other tomato 

 diseases attributed to bacteria. The wilt disease caused by Bacterimn 

 solanaccmum, Erw. Sm. is a distinctly vascular trouble, and causes a 

 characteristic wilting of the plants. AjyJanoharfer wichirjanense is 

 also found in the vessels. "Streak," described by Paine and liewley 



