1920.] 



Stripe " Disease of Tomatoes. 



999 



are allowed to develop, although it is not unusual to find the 

 disease in the spring when the lirst pickings are being made. 



The plants are generally attacked underground, the causal 

 organism being introduced into the cortex of the root or stem 

 through wounds caused by biting insects. The aerial parts of 

 the plants are likewise subject to infection through insect bites, 

 and also by the organism being carried on to them by the 

 pruning knife. 



The organism travels through the stem in the parts of tlie 

 pith adjacent to the vascular bundles, and is rarely to be 

 found in the wood elements themselves. From the pith the 

 disease passes by way of the medullary rays to the cortex, 

 forming lesions in the outer cells and causing the sunken 

 furrows to be formed at the surface. The attacked tissue 

 becomes stained a dark brown colour and, on cutting the stem 

 or petiole, the diseased patches can at once be recognised by 

 the naked eye. The organism enters the fruit through the 

 stalk and finds its way to the outside by channels which, 

 when the fruit is cut open, can often be seen as narrow- brown 

 streaks in the neighbourhood of the vascular bundles ; in the 

 same way the seed may become infected or, if not actually 

 infected, since it has often been found in the loculus, the 

 organism may be dried upon the seed coat so that on germi- 

 nation the young seedling may become infected. 



The causal organism is a small, yellow bacillus closely related 

 to, if not identical with, Bacillus lathy ri (Manns and Taubenhaus), 

 which causes a very similar disease in the sw^eet pea. 



Varieties of tomatoes differ markedly in their susceptibility 

 to the attack of this organism ; " Kondine Red " and " Comet " 

 were found to be much more affected than " Ailsa Craig " when 

 grown on the same soil and under the same conditions. 

 Generally, those varieties which show rapid, soft growth in the 

 early stages are the most susceptible. 



Manurial treatment has considerable influence upon the 

 susceptibility of the plants. As has been frequently shown in 

 connection with other diseases, excessive nitrogen and a lack of 

 potash in the fertiliser tend to lower the resistance of the plant 

 to the invasion of the parasite. The effect of too much 

 nitrogen can be largely counteracted by an increase in the 

 amount of potash. 



Preventive and Remedial Measures. — i. Bacteria have been 

 isolated from the loculi of tomatoes which before cutting 

 showed very little sign of disease ; hence, owing to the difiicuity 

 experienced in thoroughly removing the glairy coating from 



