May IS. 1919 Influence of Soil Environment on Roetrot of Tobacco 43 



favorable for normal plant growth, hence preventing maturity of the crop 

 until seasonal conditions develop more favorable for the normal growth 

 of the host, but at the same time unfavorable for the development of the 

 parasite. On the other hand, the parasite has produced through this 

 indirect action heavy losses due to hail or frost injuries, or has reduced 

 the quality of the product as a result of extending the ripening and cur- 

 ing process into unfavorable seasons. No above-ground symptoms of 

 rootrot are more common than the failure of tobacco to grow appi^ciably 

 during the first month or six iX^eeks after transplanting to the field, fol- 

 lowed by a period of relatively rapid growth and development caused by 

 a change of conditions which have up to the present remained more or 

 less obscure. 



No detailed description of the disease on the roots need be given here, 

 as this phase of the subject has been frequently presented and will become 

 more or less evident in the progress of the present discussion. 



REVIEW OF THE LITERATURE 



Peglion (20) was the first to describe T. hasicola as a parasite of tobacco 

 when he reported it from Italy in 1897. There is considerable evidence, 

 however, that this disease had occurred upon tobacco in America many 

 decades prior to that time, although it was not recognized as a disease. 

 When Jones, according to Tatham {24), as early as 1724, wrote with 

 reference to agriculture in Virginia — 



when land is tired of tobacco, it will bear Indian corn or English wheat or any other 

 European grain or feed with wonderful increase — 



he made a statement which is being annually "rediscovered" by hun- 

 dreds of tobacco growers, but which is an established principle with 

 thousands of other growers. It is now quite certain that parasitism 

 explains the majority of the modern tobacco growers' difficulties of the 

 nature referred to above, and no hypothesis yet formulated will explain 

 with equal satisfaction the observations of the early Virginia planters. 



Antedating the first report of the parasitic origin of the rootrot by 13 

 years, Killebrew (77) in 1884 wrote: 



In some years the plants both in the seed bed and after being set out are affected 

 by a disease known as the " black-root. " The plants so affected do not die, but after 

 standing comparatively still for a long time revive later in the season, but do not make 

 a good quality of tobacco. It is not known what the agencies are producing this 

 disease, nor has there been a remedy discovered for it. By some it is believed to be 

 the result of sowing seed continuously in old beds. Seed beds in newly cleared 

 groimd are said to be entirely free from it. 



There can be no doubt that this is the description of the rootrot, or 

 blackrot, of tobacco caused by T. hasicola. This brief description of 

 the disease is given in full, since it is probably not only the first authentic 

 report of the disease but also because it describes the common behavior 

 of infected plants, as follows: 

 after standing comparatively still for a long time revive later in the season. 



