la. 



factor. On resistant plants only a very small nimiber 

 of small mostly empty cysts are formed. However, a 

 good number of. males completes development to the adult 

 stage. The testing of the plants can easily be done hy 

 growing them in pots with infested soil. 



After SIX years of breeding a few very promising 

 varieties are ready to be released. 



Recently a race of ino potato cyst eelworm has 

 been foiina, both in England (JUW'^ 19b>7) ana in tne 

 Netherlands, wnich attacks tne originally resistant 

 material. 



C. hesisLance of beets against Heteroaera schactii 



Despite repeated efforts, no Beta species resistant 

 against the beet cyst eelworm which can be crossed with 

 Beta VTilgaris have been found. 



3. Crop rotation 



The possibilities of crop rotation are discussed in the 

 following lecture. It is particularly effective against Heter- 

 odera species, when the farmer can afford to grow susceptible 

 crops with several years intervals. As with several other 

 nematodes, rotation possibilities depend on soil type, crop, 

 or both and often it has no effect at all. 



