50 MASS. EXPERIMENT STATION BULLETIN 202. 



Vakietal Susceptibility. 



The list of commercially grown varieties of snapdragon, such as, for 

 example, Nelrose, Silver Pink, Phelp's Wliite and Keystone, is not large. 

 But there is a large number of varieties listed and grown outdoors. Since 

 there seemed to be but little information available as to which varieties 

 are resistant and which susceptible, the writer tested forty-six varieties. 

 The plants were grown from seed, and when the potted plants had reached 

 a height of 6 inches they were inoculated by being sprayed with water 

 in which urediniospores had been distributed, and placed under bell jars 

 at 10° C. Each variety tested was represented by twelve to twenty 

 individuals. 



Two weeks after the date of inoculation the plants were examined 

 and the number of rust pustules and infected leaves were counted. The 

 plants were examined at weekly intervals for the next five weeks, and 

 observations recorded as to the number of rust pustules and infected 

 leaves. In the following table the varieties are grouped according to 

 color, and under each color the most resistant varieties are named first, 

 and the most susceptible varieties are named last, the intermediate 

 varieties being so arranged that any variety is more resistant than those 

 which follow it. Varieties equally resistant or susceptible are connected 

 with brackets. By means of the relative numbers in the table it is possible 

 to compare varieties of different colors as regards resistance. 



Unfortunately, the most valuable commercial varieties, such as Nelrose 

 and Silver Pink, are very susceptible to the rust. 



The following table is perhaps not of great value to florists, since they 

 must grow the varieties most in demand. But this table of relative 

 susceptibility could be used as a basis in breeding resistant varieties, 

 and by its use the amateur grower of snapdragons can avoid the more 

 susceptible varieties, and still have a satisfactory garden of snapdragons. 



