13. 



Europe snow a certain degree of resistance against 

 the rye race of the stem eelworm. As early as 1910 

 some breeding had been done by an agronomy teacher 

 in Ottersum, "Netherlands. He applied mass selection 

 on an infested fxeld. It seems to be impossible in 

 tnis way to ootain material with more than 2b% fully 

 resistant and ;?0% somewnat resistant plants. The 

 latter group of plants always yields susceptible 

 plants in the offspring. In the field they cannot be 

 distinguished from the fully resistant plants. 



S'PlIWHUrtST (I9i>3) worked out a method for the in- 

 vestigation of seedlings in the laboratory. Here the 

 fully resistant plants can be distinguished from the 

 sligntly susceptible ones, and by tnis method plants 

 could be selected after three years of breeding work 

 in whose offspring more tnan ;pO% fully resistant and 

 no susceptible plants occurred. The breeding work is 

 now done by two professional plant breeders. 



Red clover . In South Sweden an eelworm resistant 

 variety was selected from a local variety by mass 

 selection (SYLVEW 193b). BIWGEFOhS (1937) worked out 

 a method for the investigation of clover seedlings 

 on filter paper strips in the laboratory. He selected 

 plants wtach looked completely healthy. 



SEII>;HORST (19!?b) described a difference in reaction 

 to attack of resistant and susce-^tible red clover by 

 the red clover race of the stem nematode. The sus- 

 ceptible plants show stunting and svrelling, the resis- 

 tant ones some stunting and necrosis. 



DIJKSTHA (19!??) worked out the selection of resis- 

 tant red clover on the basis of tne findmj^s of SPIW- 

 HOhST (19h)t)). Resistance of this type appeared to ocevu 

 in all red clover varieties. DIJKSTHA also found a 

 small percentage of plants which shox'/ed no symptoms 

 at all after inoculation. 



B. Resistance of potatoes against Heterodera rostochiensis 



In 19Ui? ELLEl^bj' found that some Solanimi andigrnum 

 lines were resistant against the potato cyst c«1voitii, 



TOXOPEUS and HUYS^IAN (19I?2) used tnis material as 

 a basis for breeding; an eelworm resistant potato variety . 

 The resistance appeared to be dominant and based on one 



