358 DISEASES OF CROP-PLANTS 



Since wilting of the same type is produced by Fusarium dis- 

 ease, and would ensue from any other cause which cut off the 

 supply of water through the stem, it is necessary for the purpose 

 of a field diagnosis to have some further evidence of the presence 

 of this particular disease. Confirmation fairly satisfactory for 

 this purpose may be obtained by cutting across the stem at 

 intervals with a clean sharp knife. When the region of infestation 

 is reached the woody ring in the stem is found to be discoloured 

 brown, and in a short time dirty white or brownish beads of 

 bacterial ooze collect on the ends of the cut vessels. In the 

 region of serious infestation this discharge is copious enough to be 

 quite apparent to the naked eye. The pith may or may not be 

 discoloured ; the principal seat of the disease is in the vascular 

 tissues, from which circumstance, when the infestation of any 

 section of the stem is complete, the wilting of all parts of the 

 plant beyond that section follows. 



Susceptibility. 



There seems to be no evidence of varietal resistance in tomatoes 

 given in connection with the published studies of this disease. 

 Solanum mammositm is reported from Porto Rico to be resistant, 

 and the suggestion has been made to use it as a stock for grafting 

 tomato and egg-plant. At the St. Vincent Station natural 

 infection occurred to a considerable extent in American varieties 

 of the Ponderosa type (which includes Earliana). The type with 

 small round fruits, common in these islands and reputed to be 

 native, proved fully susceptible to inoculations. A bed of F 2 

 hybrids between Ponderosa and Native was with few exceptions 

 destroyed when in full bearing. It is very much open to doubt 

 whether the survivors were really resistant to the disease, in view 

 of the known lessening of susceptibility to infection in matured 

 plants. From whatever circumstances arising, some of the plants 

 did resist artificial infection at this stage, and cuttings were taken 

 from the survivors for further trial. A batch of hybrid seedlings, 

 inoculated through needle pricks when a few inches high, suc- 

 cumbed in five days, showing at the point of introduction of the 

 bacterium an infestation which was greatest in the protoxylem 

 and the immediately adjacent cortical parenchyma. Attempts 

 to infect tomato fruits with Bact. solanacearum resulted in slight 

 local injuries which developed no further. This is in agreement 

 with the results of previous investigators. 



Infection. 



The plants in which natural infections occurred were trans- 

 planted seedlings, in some cases very widely spaced, and the 

 distribution of the diseased plants was of a sporadic type. In 

 one rather close-planted row of Earliana several scattered plants 

 died when coming into fruit without infecting their neighbours^ 



