Meter: 



H. schachtii, H. trifolii , and H. galeopsidi£ where vrc have species 

 that are fairly polyphagous and attack plants in several families. They 

 may be a bit choosey in some plant families, m.issing out on some genera 

 and attacking others, but they do cover quite a range of families. As 

 far as the beet nematode is concerned, which is fairly polyphagous, the 

 two chief families are the Chenopodiaceae and the Cruciferae. Other 

 minor host families are ones like the Caryophyllaceas and Polygonaceae. 

 It is interesting to know that host range studies done by Dr. Raski in 

 the U.S.A., by Oostenbrink in Holland, and by myself and Vlinslow in 

 England, do agree very well, although there is quite a difference between 

 the source of our materials. The only difference that I have detected is 

 that in America one would include the Labiatae. We so far have not found 

 this. When we turn to the other species, species like H. major, H. 

 crucif erae, H. rostochiensis, H. tobacujn (which is fairly similarT, 

 H. gottingiana, H. hujim'li, and H. carotae, they are a good deal less 

 polyphagous and tend to attack plants in one family and sometimes restrict 

 themselves to only one or two genera. I suppose of all of these, based 

 on our present knovrledge of host ranges, which I must say is far from 

 complete, the most specialized is H. £arotai3 which attacks only one or 

 two species of the genus Daucus. I don't think we can divide up the 

 groups on the basis of host ranges beyond thisj that is, divide them up 

 soundly on the basis of scientific evidence. It is of great interest 

 that some of these host ranges overlap. For example, H. schachtii and 

 H. cruciferae may have their host ranges overlap among the Cruciferous 

 plants. This would, I think, make a very interesting bio-chemical study 

 to see what it is that these two eelworms find in their ccmumon host 

 plants and yet do not find in the parts of their host ranges which do 

 not overlap. In other words, what are these substances which go into 

 making up the differences in host ranges? The same thing is seen, perhaps 

 more acutely, with H. rostoc hiensis and H. toba cum where we have tvro 

 very similar eelworms with a certain amount of overlapping of their host 

 ranges within the same genera, Solanum and Nicotiana. This would be a 

 very interesting study indeed for a bio-chemist. 



Well now, it is all very well to study a host range and find which 

 plants are attacked, but there are varying degrees of host efficiencies 

 in raising the nematode population. There are some hosts that are more 

 efficient than others and that is a matter of some importance to the 

 farmer. There are, in fact, two attributes of host plants. One is this 

 business of supporting invading nematodes and the production of new cysts 

 and the other is susceptibility to invasion by the nematodes. I submit 

 that these two things are not necessarily related. For example, in H. 

 schachtii you have a host like the sugar beet which is an efficient 

 plant, but which is highly susceptible to injury by the larvae. On the 

 other hand, you have in the Cruciferae plants which are perhaps even 

 more efficient in raising the nematode population, but which don't suffer 

 to anywhere near the same extent due to larval invasion. If you vrere 

 to put sugar beets and these crucifers in the same soil, the sugar beet 

 may collapse whereas the crucifers may continue to grow showing only a 



