628 MICROBIAL DISEASES OF PLANTS 



Causal Organism. — Erwin F. Smith describes Bacillus tracheiphUus as a rod 

 1.2/4 to 2.5/i by o.Sft to 0.7^1, actively motile when young. 



Growth occurs on the ordinary media. Upon agar, the growth is milk-white and 

 extremely viscid. Upon potato, a gray film is produced, much like that of B. 

 typhosus; the potato is unchanged. Gelatin is liquefied and no change occup in 

 milk. Acid but no gas is produced in saccharose and dextrose broths. The organ- 

 ism is aerobic and possibly facultatively anaerobic. Optimum temperature is 

 between 20° and 30°. No growth at 37°. Thermal death-point, 43°. 



Control. — ^The same precautions and preventative measures are to 

 be recommended for the wilt of cucurbits as are given for tomato 

 blight. 



Wilt of Sweet Corn 

 Pseudomonas stewarii — Smith 



The early varieties of sweet corn grown in the truck gardens of Long 

 Island* are subject to a bacterial disease which manifests itself by a 

 wilting and dr3dng up of the leaves. It also occurs in Iowa, and it 

 has been reported from certain parts of New Jersey. 



The wilting may occur at any stage of growth, but the plants seem 

 to be inore susceptible at the time of flowering. As a rule the leaves 

 succumb onei at a time, although on the younger plants they may all 

 wilt simultaneously. There is no external evidence which would 

 indicate the cause of the trouble, but if a diseased stalk is cut length- 

 wise, the fibro-vascular bundles appear as yellow strands in the white 

 pith. A cross-section of such a stalk will show drops of a yellow viscid 

 substance, composed largely of bacteria, exuding from the cut ends of the 

 bundles. The infection is not confined to the stalks but can be found 

 in the vascular system of the leaves, husks and cobs as well. The 

 vessels are the principal structures invaded, but in time small cavities 

 filled with the bright yellow slime are formed in tlie surrounding 

 parenchyma. 



Method op Infection. — The germ may enter its host through 

 either the roots, stomata or water pores and when once inside the vas- 

 cular system, it multiphes very rapidly and fills the water tubes with a 

 yeUow slime and wilting follows. 



Causal Organism. — The organism was first described by Stewart and later 

 named Pseudomonas stewarti by Erwin Smith. 



* Stewart, F. C, "A Bacterial Disease of Sweet Corj," Bull. 130, N. Y. Agr. Exp. Sta., t897- 



