246 MASS. EXPERIMENT STATION BULLETIN 280 



individual plants within these strains which seemed to be satisfactorily resistant 

 Eight of the new strains seemed to be approximately as resistant to black root-, 

 rot as Havana 142 A3, as determined by comparision of producng capacities 

 and infections of black root-rot when grown in soil which was heavily infested 

 with Thielavia basicola. 



The producing capacitj'^ of the four common strains, of Havana 142A3, 

 and of these eight new strains, as indicated by the yields in 1930 on soil free or 

 nearly free of Thielavia basicola, are shown in the following table: 



Eight of the eleven new strains were satisfactory for resistance to black root- 

 rot and for yielding capacity; but one of these eight was definitely unsatis- 

 factory for type of plant and type and quality of leaf, and for this reason was 

 discontinued. Thus far it appears that seven of the new strains of Havana Seed 

 may be acceptable for resistance to black root-rot, type of plant, type and 

 quality of leaf, and yielding capacity. These deserve further testing. 



Mosaic. (C. V. Kightlinger). It has been determined experimentally that 

 tobacco mosaic virus, contained within tobacco debris mixed with moist sandy 

 loam soil, clay soil, or sandy soil and kept under out-of-doors conditions except 

 for leaching, in each case retained its viability for two seasons sufficiently to 

 produce infections of mosaic when suspensions of such mixtures of soil and 

 debris were inoculated into healthy tobacco plants by the needle method. 



In inoculation tests by the needle method, it has been found that formalde- 

 hyde, acetic acid, and several other substances, when mixed directly with the 

 expressed juices of mosaic-diseased tobacco plants, were able to inactivate the 

 virus sufficiently to prevent infections. Whether these chemicals, when used as 

 seedbed disinfectants in the usual manner and in the usual amounts and con- 

 centrations, may be able to inactivate the mosaic viruses contained in seedbed 

 soil, has not been definitely determined. Preparations have been made for final 

 tests of this point, and the actual tests will be made next spring and summer. 



