2 BULLETIN 1015, U. S. DEPARTMENT OF AGRICULTURE. 



Plate I, figure 2. Not infrequently whole fields of plants wilt in 

 this manner (PL II, fig. 1) and finally succumb to the disease. 



In cross and longitudinal sections of infected stems (PI. Ill) there 

 is a dark-brown discoloration in the woody area between the pith 

 and the bark, but the pith itself is usually normal. The presence 

 and position of this discoloration are important diagnostic char- 

 acters which help to distinguish the wilt from another similar dis- 

 ease known as southern bacterial blight (bacterial wilt). 



Not only the stems and leaves but also the fruits are infected by 

 wilt (PI. II, fig. 2). By means of the discolored tissues infection 

 can be traced through the fruit stems into the fruit and even to 

 the seed. 



Yearly discoveries of wilt where it has never previously been 

 found indicate that it is either continually spreading or is not 

 infrequently present where it has never been reported. Observa- 

 tions and reports show that both of these conditions obtain. 



It is probable that wilt will eventually spread over the greater 

 part of the tomato-canning areas if not prevented by the use of 

 resistant varieties. Although the wilt fungus may not thrive so 

 well in the North as it has in the South, the fact that it is continually 

 spreading in some of the more northern States, such as New Jersey, 

 Indiana, and Ohio, and has even been found in Michigan, New York, 

 and Massachusetts, shows that it is seemingly capable of thriving in 

 the more important tomato-canning regions of the United States. 



Wilt is carried to some extent by the seed, but not so commonly 

 as the high percentage of fruit infections in wilt-infested fields would 

 seem to indicate. The fungus passes through the fibro-vascular 

 bundles of the fruit to the seed and often invades the cells surround- 

 ing the seed coat. Were it not for the removal of these cells through 

 fermentation and washing of the seed in the seed-saving process the 

 infection of plants through the seed would be much more common. 

 The fungus-bearing particles separated from the seed by fermenta- 

 tion frequentl}' adhere to it, however, and thus become a source of 

 infection for the plant and a means of more widespread distribu- 

 tion for the fungus. Infection of plants through the seed would 

 be more common if tomato seed was produced commercially in badly 

 wilt-infested regions. 



The most common method of spreading wilt is through infected 

 seedlings. Tomatoes are very generally grown in seed beds and are 

 transplanted to the field when danger of frost is past. Not infre- 

 quently the fungus occurs in the seed-bed soil in wilt-infested 

 regions. As such soil is usually rich in organic matter the fungus 

 multiplies rapidly and soon invades the roots of the seedlings. 

 Although this causes a discoloration of the rootlets, the grower, who 

 not infrequently is unfamiliar with plant diseases, usually fails to 



