16 MASS. EXPERIMENT STATION BULLETIN 388 



black root-rot or in habits of growth. Earlier maturity, which was greatly de- 

 sired, was not obtained in any of the selections of Havana 21L Some of the 

 selections from the crosses possess sufficient resistance to yield well under black 

 root-rot conditions in the Connecticut Valley, and also show distinct improve- 

 ments in important characteristics of type and habits of growth, including earlier 

 maturity. Some of these selections are as early maturing as the strains of common 

 Havana Seed which were used in making the crosses. They seem, also, to be supe- 

 rior to either parent in some important characteristics such as shape of leaf and 

 size of veins. These particular strains deserve more testing to determine their 

 full resistance to black root-rot and also to determine the permanency of the im- 

 provements in type and habits of growth which have been manifested so far. 

 It seems reasonably certain, however, that definite progress has been made. 



Brown Root-Rot. (C. V. Kightlingcr.) Brown root-rot causes some damage 

 to tobacco in the Connecticut Valley at the present time and probably would 

 cause much more damage if it were not that the circumstances under which the 

 disease ordinarily occurs are now known and are avoided in large measure in 

 present practices of growing tobacco in the Connecticut Valley. The practices 

 of not rotating tobacco with crops known to produce soil conditions favorable to 

 the development of brown root-rot and of growing tobacco continuously after 

 tobacco for as long a time as may be possible are applicable in the control of the 

 disease where the acreage of tobacco is being maintained or reduced somewhat, 

 as has been the case in the Connecticut Valley during the last few years. This 

 method of control, however, is restrictive and is not always convenient to follow 

 even under present circumstances, but the rather dilligent application of the 

 practice has reduced the prevalence and severity of the disease so that it has been 

 of minor importance economically in the Connecticut Valley during the last 

 several years. 



Brown root-rot may become more prevalent and injurious in the Connecticut 

 Valley in case of an increase in acreage of tobacco, because of the necessity of 

 using additional land which, on account of previous cropping, may be in a condi- 

 tion favorable to the development cf the disease. If this occurs, it will contravene 

 the only measure for the control of brown root-rot of tobacco which is generally 

 recognized at the present time as being applicable to field use. Thsrefore, a meas- 

 ure which would control brown root-rot of tobacco satisfactorily under varied 

 circumstances and which would be convenient to use on considerable acreages 

 would mean much to the growing of tobacco in the Connecticut Valley in the 

 event that the acreage is increased. Such a measure would be useful also under 

 present circumstances, especially if it would permit rotation of tobacco with other 

 crops in general. 



With this situation in mind, experiments were begun in 1939 to obtain further 

 information on the relationship of soil fertility conditions to the development 

 and to the control of brown root-rot of tobacco. One purpose in particular is to 

 study the effect of certain soil treatments on the fertility levels of the soil and to 

 study the effect of different degrees of fertility of the soil on the occurrence of 

 brown root-rot of tobacco following the crops used in the experiment. It is 

 desired especially to learn whether brown root-rot will develop in tobacco which 

 is grown continuously after tobacco under low fertility conditions of the soil. 

 And finally, in case brown root-rot of tobacco develops as a result of these ex- 

 periments, another purpose is to study means of hastening recovery. 



The arrangement and procedure of the experiments designed to determine 

 whether low fertility of the soil may promote the development of brown root-rot 

 of tobacco, consists of four sets of six one-twentieth acre plots in which tobacco, 

 corn, millet, rye, clover, and timothy-red top mixture are grown in the same 



