BROWN CANKER OF ROSES, CAUSED BY DIAPORTHE 



UMBRINA 



By Anna E. Jenkins 



Scientific Assistant, Office of Pathological Collections, Bureau of Plant Industry, United 



States Department of Agriculture 



INTRODUCTION 



In April, 1917, an apparently unreported fungus disease producing 

 a canker on stems of rose {Rosa spp.) was brought to the attention of 

 the Office of Pathological Collections. In the National Rose Test Garden 

 at the Arlington Experimental Farm, Virginia, where over 900 named 

 species and horticultural varieties of roses are grown, nearly all were 

 affected. All the brier roses, the rugosas, the moss roses, some of the 

 ramblers, and most of the named species were unaffected. The canes 

 had been badly injured the previous season by a severe hailstorm, and 

 the disease in some cases had gained entrance through these wounds, 

 although there were many instances of infection where external injury 

 could not be detected. The cankered canes were cut out and burned, 

 and to all appearances the new growth was healthy. When observed 

 in March, 191 8, although there was no evidence of hail injury, the canker 

 was again equally as prevalent as in 191 7, thereby necessitating the 

 severe cutting back of the plants. 



The disease appears to be more or less widely distributed, speci- 

 mens having been received from Georgia, Virginia, West Virginia, and 

 the District of Columbia. The dates of these collections range from 

 1903 to 1918. In June, 1918, Dr. L. M. Massey, Plant Pathologist at 

 Cornell University, who has given special attention to rose diseases, 

 forwarded to this laboratory a culture made from rose material collected 

 in Connecticut. A comparison of this culture with the fungus isolated 

 by the writer showed that the two organisms are identical 



CHARACTER OF THE DISEASE 



This canker may occur on any portion of the cane, diseased areas being 

 raw-umber in color, sometimes surrounded by a purple border (PI. 46, B). 

 The cankered surface is dotted with fruiting bodies, the pycnidial and 

 ascosporic stages of the parasite. In mature specimens the small 

 protruding beaks of the perithecia may be seen. The margin of a canker 

 is generally defined only by the difference in color between the normal 

 and cankered portions, and to this contrast in color is due the conspicu- 

 ous and disfiguring effect of the disease (Pi. D). The canker differs in 

 color and appearance from the common canker caused by Coniothyrium 

 juckelii Sacc. In color the latter canker is a Roman sepia or dirty 



Journal of Agricultural Research, Vol. XV, No. ii 



Washington, D. C. December i6, 1918 



qs Key No. O-168 



(593) 



