Feb. i8, 1918 Tobacco Wildfire 451 



appeared so quickly, spread so rapidly, and affected the leaves so seri- 

 ously that it was commonly given the appropriate designation "wildfire." 



The foliage alone seems to be subject to attack. The first evidence 

 of disease is the appearance of circular, chlorotic areas varying from 0.5 

 to I cm. in diameter. Within 24 hours after this chlorosis is first noted 

 minute brown areas will have formed at the centers of the spots (PI. 

 15, A). Within another day these spots will have enlarged greatly 

 PI. 15, B), and a border of water-soaked appearance marks the margin 

 of the necrotic tissues. Within a few more days the diseased areas are 

 2 to 3 cm. in diameter and are often strikingly concentric with shades 

 of tan to dark brown, the centers being lightest in color (PI. 16, A). 

 Such spots have a broad translucent border, which is in turn surrounded 

 by a chlorotic halo that pales out into adjacent tissues (PI, 15, B; i6, A). 

 When the spots are numerous, they fuse, causing large, irregular areas 

 of leaf tissue to become dry. These dead areas remain intact in case 

 there is no precipitation. When dewy nights and intermittent showers 

 occur, however, the dead areas rot out so that the leaves present a ragged 

 appearance (PI. 16, C) which is especially manifest when large numbers 

 of infections occur upon a single leaf. 



Not uncommonly the leaves on one side of the plant are more seriously 

 diseased than those on the opposite side and there may even be a uni- 

 lateral destruction of these leaves resulting in distortion, as shown in 

 Plate 16, B. The vascular tissues seem not to be invaded, but the 

 organism confines its attack to parenchymatous tissues. 



Two other leaf spot diseases of tobacco, frogeye and speck, are present 

 within North Carolina, from both of which wildfire is easily distinguish- 

 able. Frogeye appears as circular, brown spots, with a darker border 

 and with grayish centers. Upon this gray center may be seen the 

 fructifications of Cercospora nicotianae E. and E., or other fungi associated 

 with the disease. No chlorosis accompanies these spots. Speck, which 

 results from a deficiency of potash, appears as tan-colored, irregular 

 areas which are first present at a distance from the principal veins. 

 When this disease is accompanied by chlorosis, there is no definite halo 

 around the lesions. In the case of neither of these diseases is the margin 

 of the affected areas water-soaked in appearance, and in neither of them 

 do the affected tissues disintegrate and fall out. 



ISOLATIONS AND INOCULATIONS 



On June 13, fresh material of tobacco wildfire was collected and 

 isolations were made by planting on poured plates of nutrient agar frag- 

 ments of tissue from the margin of affected areas. Contamination was 

 avoided by washing the leaves prior to making the planting in mercuric 

 chlorid and then rinsing them in sterile water. Several types of colonies 

 developed along the margins of these plantings, the most common of 

 which was Bad. tabacum, which appeared as glistening, grayish white 



