30, 



6» Sunimary ana conclusions 



The plant parasitic nematodes can be divided into two 

 groups . 



A. Those showing a very close relation to crops rotation 

 in their population dynamics, e.g. Heterodera species, 

 Anguina species. 



B. Those being relatively independant of host crops for 

 their persistence in the soil at a certain level of 

 infestation. This level depends on soil type. Also 

 top levels of infestation and persistence of the 

 nematodes in tne soil at higher levels of infestation 

 is highly dependent on soil type ( Dityiencnus dipsaci , 

 Pratylenchus spp., and Hoplolaimus unif oralis) ." 



In areas of optimum conditions for the nematode the 

 species of group B. show more or less the same benavior towards 

 the growing of host plants as those of group A. As, however, 

 the species of group B. mostly have a veiy wide host range 

 they also show a high persistence level under such conditions, 

 and tne effect of crop rotation on population numbers and dam- 

 age is limited. 



Demonstration of the damaging nature to plants of certain 

 nematode species combined with knowledge of its area of distri- 

 bution is an insufficient base for evaluation of its importance. 

 It is also necessary to know at wnat degree of infestation of 

 the soil damage can be expected and in what part of the distri- 

 butional area sucn degrees of infestation are likely to be 

 built up under cropping practices favorable to the nematode. 



In some cases these areas coincide. Tnis occurs wnen 

 damage already begins at degrees of infestation just detect- 

 able with the present means of investigation. This is the 

 case with stem nematodes, Belonolaimus gracilis , and Praty - 

 lenchus penetrans on daffodils, raspberries and probably 

 some otner plants, but not on potatoes and many other host 

 plants. 



The higher the number of specimens of a certain species 

 required to cause damage the larger the ratio between distri- 

 butional area and area where damage occurs will be. 



