Dityl:2 



Kirjanova, in Russia, uses the name Ditylenchus allii , but she does not 

 give any good morphological differences. So far, we can only distinguish 

 the different forms of the stem nematode by doing host range tests. 

 Thus, the nematodes are actually host races. Even if we were to find 

 morphological differences, we should not neglect the host range test, 

 because we cannot be sure that there would not be more different forms 

 of the nematodes than we could distinguish morphologically. 



At the present time, from my own experience and from the literature, I 

 estimate that there are at least twelve host races of the stem nematode. 

 Thus, there is the question of how these different races are related to 

 one another. As far as I know, all of the races are rather polyphagous. 

 One may find large numbers of different host plants which the different 

 races have in common. There are only a few hosts where one finds differ- 

 ences. These are the plants we utilize for possible tests to separate 

 the different races. For example, the onion race of the stem nematode 

 has beeh considered for a long time to be the same as the rye race or 

 the race occurring on oats, but it does not attack teasel nor red clover, 

 and it does attack peas. However, in at least some regions of England 

 the stem nematode on onions does attack teasel and onions may be attacked 

 by the teasel race. In Holland, onions are attacked by a race which is 

 different from the rye race and different from the teasel race. So we 

 can go on and by host testing make twelve races of the stem nematode. 



Different forms of the stem nematode are distinguishable by different 

 reactions of the plants to the presence of these nematodes. It is not 

 just simply attack resulting in symptoms or no symptoms, m-ultiplication 

 or no multiplication. There are different kinds of symptoms. Feeding 

 and multiplication of the stem nematodes seem always to go together 

 tidth one parti ular symptom, and that is dissolution of the middle lamella. 

 Wlien stem nematodes invade the parenchymous tissues, the middle lammelae 

 begin to dissolve and finally the cells are lying loose within the tissue. 

 They cannot, of course, stay alive for a long time like this, so they die 

 soon. If you were to take an attacked rye or onion plant, for example, 

 and place some of the infected tissue in water, you would see that the 

 cells just fall apart from each other. In addition to brcakdovm of the 

 middle lamellae, in most plants there will also be swelling. Dissolu- 

 tion of the lamallae causes swelling because the intercellular spaces 

 become larger. At the same time, the presence of more air in these 

 spaces make the tissues appear whitish or silvery. Also, other disease 

 symptoms may be found. Ifepecially in growing parts of the plants, there 

 may occur distortions, stunting, swelling, and development of extra 

 parts or extra tillering in onions and in cereals. 



^ In the case of rye field plantings, attack by the stem nematodes 

 most3.y occurs in patches and the affected plants are stunted. In the 



•55- Editor's note: Beginning at this point. Dr. Seinliorst presented a 

 series of lantern slides illustrating symptoms of disease caused by 

 DJtylenchu s. Some of his descriptive comments are incliidcd here for 

 their value even though the illustrations arc not repx-oduccd. 



