BASAL GLUMEROT OF WHEAT 



By Lucia McCulloch 



Assistant Pathologist, Laboratory of Plant Pathology, Bureau of Plant Industry, 

 United States Department of Agriculture 



In the course of an examination in this laboratory of various col- 

 lections of wheat of the crop of 1917 made for the study of "black chaff," 

 a bacterial disease unlike "black chaff" or any other reported wheat 

 disease was discovered ; and this same disease was observed again several 

 times in the collections of 191 8. 



This disease affects the leaf, head, and grain of wheat. On the heads 

 the glumes show at the base a dull brownish black area. Sometimes this 

 dark area extends over nearly the whole surface of the glume; but 

 usually only the lower third, or less, is darkened (PI. 62, A, B) ; and often 

 no discoloration is visible on the exterior. Glumes that have a normal 

 color on the outer surface may have the inner surface discolored. In 

 practically all cases, dissection of the spikelet reveals more signs of disease 

 on the inner surfaces than on the outer. Often a narrow dark line at the 

 junction of the spikelet and the rachis is the only outward sign of the 

 disease. 



The grain inclosed by such diseased glumes shows varying degrees of 

 undevelopment. The fact that grains are often well filled out would 

 indicate that the disease sometimes appears late in the course of growth. 

 In diseased grain the base, or germ end, varies in color from a scarcely 

 noticeable brown to charcoal black (PI. 62, C). In severe cases the sur- 

 face texture as well as the color suggests charring. In the discolored areas 

 bacteria are found in great abundance. Pure cultures have been secured 

 from material collected in various States and in Canada. 



This type of disease has been found in collections of wheat from New 

 York, Michigan, Kansas, Missouri, Minnesota, North Dakota, South 

 Dakota, Oklahoma, and Alberta, Canada. 



The bacterium isolated from the infected glumes and grains is a 

 medium-sized rod (i to 2.yn by o.6^^), with rounded ends; in favorable 

 media it forms long chains; it is actively motile by means of one to four 

 polar or bipolar flagella (PI. 63, F) ; and capsules are present in 6-day-old 

 beef agar cultures (Ribbert's capsule stain). 



No spores, zoogloeae, or involution forms have been observed. 



The organism is G ram -negative and is not acid-fast. 



Its staining reactions are rather feeble, but hot carbol fuchsin, 

 anilin gentian violet, and saturated gentian violet gave good results. 

 The stains must be washed out only with weak grades of alcohol (40 to 50 

 per cent), since strong alcohol takes them out too readily. 



Journal of Agricultural Research, Vol. XVIII, No. lo 



WashinKton, D. C. Feb. i6, 1920 



ts Key No. G-i8s 



156105°— 20 4 (543) 



