212 AGRICULTURE OF IMAIXE. 



A plant may be resistant to two or more diseases, or may 

 be resistant to some and subject to others, indicating that dis- 

 ease-resistance is specific. Thus Orton d i ) cites Centerville 

 cotton as being resistant to wilt, and also to black arm, Rivers 

 resistant to wilt, but susceptible to black arm and Iron cowpea 

 as immune to wilt, root knot, and Cerocospora leaf spot, but 

 subject to powdery mildew and other fungous leaf spots. 



It has been noted by various workers in obtaining disease- 

 resistant plants that plants brcfl to be resistant to a certain 

 disease in one locality have been susceptible to this disease 

 when transferred to another locality where soil and climatic 

 conditions are different. Bolley, (12) in speaking of wilt- 

 resistant flax, says that "A particular strain bred to resistance 

 is resistant for that particular grade of sick ground upon which 

 it is developed but may vary upon different soils," and that ''A 

 certain percentage of wood ashes added to the soil is sufficient 

 to break down the resistance which is otherwise perfect." 



The writer in the pursuit of his investigations on the anthrac- 

 nose of beans artificially inoculated a large number of varieties 

 to determine their susceptibility or resistance to this disease. 

 He found eleven varieties of kidney beans that were apparently 

 quite resistant or entirely immune. These, later in the year 

 when inoculated with a strain of the fungus from an entirely 

 different source proved to be as susceptible as any of the 

 others, and what is most surprising, the varieties Navy Pea 

 and Golden Refugee, which had given excellent infection to 

 the first strain gave slight or no infection when inoculated with 

 the second strain. This indicates that not only do the hosts 

 vary in constitutional ability to resist infection, but the parasite 

 itself varies in its power to infect. Subsequent experiments 

 confirmed the reliability of these results. It would seem, 

 therefore, that it is not safe to conclude because an individual, 

 a strain, or a variety is resistant from one inoculation and in 

 one locality that it will continue to be resistant from other 

 inoculations and in other localities, and the reason thereof 



11. Orton, W. A. On the Theory and Practice of Breeding Disease- 

 Resistant Plants. Am. Breed. Assoc. Rept. 4 : 144-156, 1908. 



12. Bolley, L. H. Some Results and Observations Noted in Breeding 

 Cereals in a Specially Prepared Disease Garden. Am. Breed. Assoc. 

 Rept. 5 : 177-182, 1909. 



