ROOT KNOT IN THE TOMATO. 



Bv Professor Hokac f. Athet,stax Wager, A.R.C.Sc. 



The life history of the Nematode worm Hcterodcra radicaJc 

 causing this disease in America has been fully worked out by 

 Ernest Bessey, but the results of my own observations on a 

 similar disease in the Transvaal — notably in the Tomato — appear 

 to ditfer somewhat markedly from his account, so that I am 

 doubtful if the Transvaal species is quite the same. It has been 

 thought that the worm has been introduced into South Africa 

 from America, but it is more probable that the worm is in- 

 digenous, as it has been found on uncleared and uncultivated land. 

 However, it is easy to see how the worm could be disseminated if 

 once introduced, as small quantities of soil containing the worm 

 are easily carried from one place to another by the hoofs of 

 animals, cart-wheels, etc. The list of infected plants in America 

 contains now over 500 names, whereas the South African species 

 appears to show preference for only a few hosts, having a re- 

 luctance to attack others. 1 have grown likely hosts quite close 

 to badly-infected Tomato plants without the slightest trace of 

 infection appearing. In the Transvaal it forms a most destruc- 

 tive pest on Tobacco, it being impossible to grow Tobacco in some 

 districts. It is practically impossible to cure or prevent the 

 disease, at an}' rate without great expense. The worm evidently 

 lives in the soil, and enters the root, causing the disease, which 

 shows itself on the serial portions of the plant at any time, but 

 usually just as the fruit is ripening. Pathologically, however, I 

 do not consider it as a disease, but as an animal pest which so in- 

 terferes with the work of the root as to finally kill the plant. The 

 symptoms of the attack in the Tomato appear to be as follows : — 

 The whole plant becomes covered with a soft down of small 

 white hairs, especially on the young shoots and young fruits, 

 giving the plant a whitish appearance not unlike that due to a 

 mildew fungus. The young shoots soon become stunted, the 

 leaves begin to curl and shrivel up, and the fruit ripens very 

 slowly. The plant eventually comes to consist of bare stems with 

 a few green fruits still attached. 



The significance of the w-hite down on the leaves appears to 

 be explained by an efifort of the plant to correlate the transpira- 

 tion with the lessened amount of moisture absorbed by the 

 attacked roots. The roots of most of the attacked plants are 

 found to be beset with numerous swellings, probably true galls. 

 These vary in size from about i mm. on the small rootlets to 

 large warty continuations on the thicker roots. At first they are 

 hard, but soon they begin to rot, and become soft and pulpy. 

 Some attacked plants show no galls, although the presence of the 

 worm in the root can be demonstrated. The plants do not seem 

 at all able to ofifer any resistance after once being attacked, as 



