Rea.(Dityl.)tl 



BREEDING FOR P£3ISTANCE TO DITYLEU'CHUS 

 Dr. J. W. Seinhorst 



Breeding for resistance against the stem nematode, Ditylenchus , has been 

 tried now in three agricultural crops: rye, red clover, and alfalfa. 

 The breeding work for resistance in rye is the oldest of the three. In 

 Europe there are a few varieties of rye which appear to be more or less 

 resistant against attack by stem eelworms. This disease of rye occurs 

 in Germany, Holland, Belgium and Erance. We do not know much about the 

 stem eelworm of rye in France. 



In Holland there appear to be two local varieties of rye which are more 

 or less resistant. There is one variety in Germany and one or two in 

 Belgium. The German variety .lad been reported resistant in Holland some- 

 where around 1903. Some breeding had been done just after the first 

 Vforld War on the so-called Ottersum variety. Otters-urn is a small locality 

 in the southern part of our country. Actually Ottersum rye was derived 

 from the German local variety of rye. 



The breeding in red clover has been done in the field by making crosses, 

 sowing the seed in the infested land, and doing the selection in the field. 

 Starting from material developed by field selection, it was possible to 

 improve the variety and to get reasonable commercial quality and resist- 

 ance against stem nematodes. 



The alfalfa breeding work for resistance against the stem eelworm has 

 been done in t'.e United States. Attacks by stem nematodes in alfalfa 

 seem not to be very bad in Europe. In the United State, South Africa, 

 and Australia the disease occurs more or less regularly. Breeding for 

 resistance in this crop was certainly done in the first part by field 

 selection. 



In all these crops, field selection has only limited possibilities. Take, 

 for instance, the difficulties with tye breeding. If one sows rye in 

 infested fields, one is by no means sure that all the plants will be 

 infected. To have a chance of obtaining a reasonable degree of infection 

 of rye in our country, we have to sow the rye in October or November. If 

 we chose another time of year when the breeding of rye sometimes is pos- 

 sible, we would have little chance of attack of the plant occurring. 



Although the soil is infested when sowing rye in Spring, the chance of 

 infection occurring is very small. Moreover, even in an infested field 

 and soiidng the rye at the right time of the year, the degree of infection 

 is extremely variable. So, vrhen we decided in Holland to take ud the 

 breeding of resistant rye again, we decided that a good result could be 

 obtained only by devising laboratory methods for the inoculation of the 

 rye. 



