ANNUAL REPORT, 1941 15 



5. A good stand of alfalfa was obtained in all of the hay-pasture mixtures 

 (Series II), but only weak stands were obtained when an early period of grazing 

 took the place of a crop of hay (Series I). Apparently alfalfa must be allowed 

 to become well established before grazing is begun. 



6. Bird's-foot trefoil, under the condition of these experiments, showed no 

 promise whatsoever. 



COOPERATIVE TOBACCO INVESTIGATIONS 



Conducted by the Bureau of Plant Industry, United States Department of Agri- 

 culture in Cooperation with the Massachusetts Agricultural Experiment 



Station 



C. V. Kightlinger, U. S. D. A., in Charge 



Black Root-Rot. (C. V. Kightlinger.) Black root-rot is one of the most com- 

 mcn diseases of tobacco, and probably the most important disease of Havana 

 Seed and shade tobaccos in the Connecticut Valley at the present time. The 

 disease is recognized generally as being highly impcrtant on the basis of losses 

 caused by moderate to heavy infections which are easily recognized as black 

 root-rot. Its importance is not so generally recognized when losses are caused by 

 light to moderate infections, largely because of the tendency to accept the low 

 yields as a matter of course instead of attributing them to specific causes, and also 

 because black root-rot is not always easily recognized in cases of light infections, 

 even though they may be sufficient to cause low yields. It is reasonably certain 

 that black root-rot causes light to moderate damage to tobacco in the Connecticut 

 Valley much more generally than is commonly recognized at the present time. 



An effective and convenient method of controlling the disease would mean 

 much to the tobacco growing industry. The disease and the conditions under 

 which it occurs are of such a nature, however, as to make resistance to the disease 

 the most feasible control method after soil conditions favorable to the disease 

 have become established; and the use of resistant strains, even before soil condi- 

 tions favorable to the development of the disease have become established, 

 would permit greater range in fertilizing practices, particularly in the use of lime, 

 than is otherwise advisable, which would often promote the production of better 

 tobacco. Consequently the attempt to develop strains of Havana Seed which 

 are more resistant to black root-rot and more acceptable in type, quality, yield, 

 and certain other characteristics, is being continued. The importance of the 

 disease and the prospects of eventual success seem to justify the continuation of 

 the project. 



The plan as it is being worked at the present time is two-fold. In the first 

 place, selections of Havana 211, which is itself moderately to highly resistant to 

 black root-rot under Connecticut Valley conditions but which is not entirely 

 acceptable in type, quality, and certain habits of growth, have been made to 

 improve the strain in type and date of maturity. In the second place, new strains 

 have been produced by crossing strains of Havana Seed which are resistant to black 

 ro3t-rot but not entirely acceptable in type and quality, with strains of common 

 Havana Seed which are not resistant to black root-rot but are acceptable in type 

 and quality, in the hope of obtaining new strains which embody the desirable 

 features of both parents. 



Tests of the selections of Havana 211 and of the crosses have been made, and 

 are being made, in the greenhouse and in the field, to determine their value. 

 Some of the selections of Havana 211 show improvements over the original 

 strain in certain characferistics, but little if any improvement in resistance to 



