Feb. 24, 1919 



Angular-Leaf Spot of Tobacco 



225 



Table III. — Comparison of Bacterium, angulatum and Bact. tabacum 



Bad. angulatum. 



Bact. tabacum. 



1. Size, 0.5X2-2.5 At 



2. 3 to 6 polar flagella 



3. lyiquifies gelatin rapidly 



4. Forms acid with saccharose and dex 



trose. 



5. No growth in closed arm of fermenta 



tion tubes. 



Size, 1.2X3.3 At. 



I polar flagellum. 



Liquifies gelatin slowly. 



Forms acid with saccharose, dextrose, lac- 

 tose, and glycerin. 



Growth in closed arm of fermentation tubes 

 containing dextrose and saccharose. 



An unsigned note in the Yearbook of the Virginia Department of 

 Agriculture and Immigration (5) contains a report of a field investigation 

 of a spotting of tobacco leaves (evidently angular-leafspot) which was 

 prevalent in Pittsylvania and Mecklenburg counties in 191 7. The 

 spotting is assigned to microorganisms, and it is stated that the disease 

 becomes serious only under certain conditions which affect the resistance 

 of the tobacco plant. The most important of these are considered to be 

 rainfall and excess of nitrogen in the fertilizer or soil. A liberal supply 

 of potash is said to decrease the severity of the disease, but considerable 

 damage was noted even with heavy potash applications. The same 

 disease is said to occur in North Carolina and Maryland. 



Two other leafspots, the causes of which have not been assigned to 

 bacteria, and which appear somewhat similar to angular-leaf spot, are 

 "rust" of tobacco in Connecticut (7, p. 366-^67, pi. 31, b, c) and Pock- 

 enkrankheit (6, p. 56) of tobacco in Europe. Clinton's figures of rust, 

 especially that shown in his Plate 31, c, look much like angular-leafspot. 

 He states that rust is usually found on leaves affected with calico and 

 believes it may be caused by scorching of the sun. Pockenkrankheit is 

 ascribed to excessive transpiration accompanying decreased water supply. 



OCCURRENCE OF THE DISEASE 



It seems quite probable that angular-leafspot is a disease of rather 

 general distribution and one of long standing which has not been suf- 

 ficiently destructive to attract extensive notice, except in seasons un- 

 usually favorable for its development. Our experience indicates that 

 rainfall accompanied by subnormal temperatures favors infection by the 

 leafspot organism and that any combination of conditions which pro- 

 motes a rapid, succulent growth of the host favors the development of 

 the organism within the leaf tissue. It seems quite probable that in- 

 fection may be common in some seasons, but that in the absence of the 

 predisposing growth factors little development ensues, and no damage 

 results. 



