76 



PROTECTIOI^J OF PLAISTS, 1920-21 



organism of bean anthracnosc will be used to illustrate both the possibilities 

 and the difficulties of this method of immunization of plants. A few illustra- 

 tions from work dbne along this line with other crops will be inicluded for pur- 

 pose of comparison and of more fully demonstrating the possibilities of this 

 phase of investigation. Biff en (16) and Nilsson-Ehle (17) were each able to 

 secure a member of hybrid wheats resistant to yellow rust from the segregates of 

 crosses between resistant wheats and those susceptible to this disease. Orton 

 (18) obtained the wilt resistant water-melon Conqueror by crossing the citron 

 and watermelon. Tisdale (19) was able to secure a hybrid strain of flax resis- 

 tant to flax wilt by crosses between resistant and susceptible varieties. 



In the case of bean anthracnose two strains of the causal organism have 

 been isolated by Barrus, (20) and the resista'nce and susceptibility to these 



H J 



Figure .3. — Four varieties of beans that have been inoculated with strain A. of the bean anthracnose 



fungus. 



Figure 4. — The same four varieties (see Fig. 3) inoculated with strain B. of the bean anthracnose 

 fungus. It is evident that variety No. 1 is resistant to both strains, variety No. 2 resistant 

 to the A. strain but susceptible to the B. strain, variety No. 4 susceptible to the A. stram but 

 resistant to the B. strain, while variety No. 6 is suceptible to both strains of the fungus. 



