A FUNGOUS DISEASE OF HEMP 



By Vera K. Charles, Assislant Mycologist, and Anna E. Jenkins, Scientific Assistant, 

 Office of Pathological Collections and Inspection Work, Bureau of Plant Industry 



In September, 191 3, the attention of the Office of Pathological Col- 

 lections and Inspection Work was called to a fungous disease which had 

 attacked a variety of hemp {Cannabis saliva) grown for experimental 

 purposes by Mr. L. H. Dewey, Botanist in Charge of Fiber-Plant Investi- 

 gations. Although the disease did not make its appearance until the 

 plants were almost full grown, it was very rapid in its action, only about 

 two weeks having elapsed between the time that the disease was first 

 noted and the death of many of the plants. One of the early symptoms 

 of the disease was the wilting and drooping of the leaves. The foliage 

 turned brown and finally died, but remained attached to the plant longer 

 than in the normal condition. In nearly all instances the fungus first 

 attacked the outer ends of some of the upper, though rarely the highest, 

 branches of the plant. In some cases the branches above and below the 

 diseased area remained uninjured for some time. It was observed that 

 the disease spread more above than below, but that the affection of the 

 plant became general in about two weeks. Although the disease ap- 

 peared to attack the outer ends of the branches first, the main stem below 

 the base of the diseased branch became bleached and afterwards dark- 

 ened by the formation of the perithecia of the fungus (PI. XI).' 



The hemp was grown from seed originally introduced from China, 

 having been grown for experimental purposes during a period of 10 years. 

 Its cultivation had been generally successful, and until the season of 1913 

 no difficulty had been experienced from fungus attack. 



All of the plants in the plots in which the disease was most serious were 

 from the seed of one single selected plant, the third best of the crop of 

 191 2. This plant showed no evidence of disease and was remarkable 

 for its purple-colored foliage. Selections had been continuous for 10 

 generations without any admixture of other strains. Three or four 

 plants of this plot which were especially precocious were marked as soon 

 as it was observed that they were pistillate, and each one of these plants 

 was attacked by the disease. So general was the attack that among the 

 135 pistillate plants of this plot 128 were destroyed by the fungus, 

 representing a loss of about 95 per cent of this plot. Later the disease 

 appeared in a larger plot of 320 and in less than four weeks 66^ per cent 

 of the plants had been attacked. 



A microscopic examination of the first diseased material collected on 

 September 12, 1913, revealed the presence of small, black pycnidia, 

 containing minute, hyaline spores on branched conidiophores. These 

 characters, together with the absence of stroma, placed the fungus in the 

 genus Dendrophoma. (Fig. i, E and F.) This appears to be the first 

 occurrence of the fungus in America. A second examination of the dis- 

 eased hemp about three weeks later showed pycnidia containing spores 



' Most of the field observations were made by Mr. L. H. Dewey, who mentions the occurrence of this 

 disease in an article entitled "Hemp" in the Yearbook, U. S. Dept, of Agriculture, for 1913, p. 283-346, fig. 

 17-21, pi. 40-46. 1914. 



Journal of ACTicultural Research, Vol. Ill, No. 1 



Deiit. of Agriculture. Washington, D. C. Oct. 15, 1914 



G-33 



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