82 



Journal of Agricultural Research 



Vol. XVII. No. 2 



in the early stages of growth, must penetrate this infested soil before 

 reaching large areas of uninfested soil. The ability to resist the disease 

 will therefore determine roughly the number of roots and rapidity with 

 which they pass through this infested area and become established, and 

 should be roughly proportional to the resistance of the different varieties 

 under similar environmental conditions. 



To determine the influence of transplanting varieties differing widely 

 in relative resistance to the rootrot, ii such varieties were sown in a 

 seed bed infested with T. basicola, and also in a sterilized bed as controls. 

 The relative resistance in the seed bed is about the same as that in the 

 field. The susceptible varieties especially did very poorly in the infested 

 beds, but most of them reached a sufficient size for transplanting. About 

 40 plants of each variety from infested soil and the same number from 

 uninfested soil, were then transplanted side by side in uninfested soil 

 (PI. 5, V). The results are given in Table XI in which the green weights 

 of 25 healthy plants and 25 diseased plants of each variety are shown, 

 together with the decreases in weight due to the use of infested seedlings. 

 It will be noted that a reduced yield occurred in all cases, but whereas 

 the disease was small in the case of varieties known to be resistant to 

 T. basicola it was relatively very high in those varieties which are sus- 

 ceptible. The results are not exactly comparable on this basis on account 

 of the difference in yield of varieties under normal conditions but serve 

 to illustrate the point in question. 



Table XI. — Influence of transplanting diseased tobacco plants in uninfested soil 



Variety. 



White Burley 



Maryland Broadleaf 



Big Oronoco 



Yellow Pryor 



Pennsylvania Broadleaf 

 Kentucky Greenleaf. .. . 



Italia Kentucky 



"Pease Seed" 



Ohio Seedleaf 



"Northern Hybrid". . . 

 Brasile Beneventano. . . 



Weight of 25 green plants. 



Healthy 

 plants. 



Gm. 

 66. 50 

 65. 00 



57-75 

 59.00 

 82. 50 



49-75 



60. GO 

 49. GO 

 70. 50 

 65. GO 

 56.50 



Infected 

 plants. 



G7n. 

 25. 00 

 38.00 



32- 50 



35- 50 

 27.25 



33- 50 

 49. 00 

 40. 00 

 51. 00 

 55- 00 

 53- 00 



Decrease 

 due to 

 disease. 



Gm. 

 41. 50 

 27. 00 



25-25 

 23- 50 



55-25 



16. 25 



II. 00 



9. CO 



19-50 



10. 00 



3-50 



Gilbert {12) reports an experiment in which "Havana Broadleaf" 

 tobacco was used and in which the yield from infected and healthy 

 plants was practically identical. By "Havana" Broadleaf was meant, 

 it is presumed, the relatively resistant variety better known as "Con- 

 necticut Broadleaf. ' ' If environmental conditions were favorable for the 



