MOSAIC OF SUGAR CANE AND OTHER GRASSES. 15 



OTHER HOSTS. 



A number of other grass plants are known to be subject to the 

 mosaic disease, but apparently they are attacked with difficulty 

 and only under conditions favorable to the disease. Among these 

 hosts are corn, sorghum, rice, millet, crab-grass, foxtail, and Panicum. 

 Probably the list of susceptible plants is much larger, but up to the 

 present time opportunity for testing others has not been had. In 

 the case of corn, rice, and millet, we have no experimental proof that 

 the diseases are the same, but must depend upon field observations. 

 If not the same, the disease must be very similar, since the leaf 

 symptoms are identical. The characteristic streaked and spotted 

 appearance of the leaves is present in all attacked plants. 



With regard to sorghum, crab-grass, foxtail, and Panicum our 

 evidence is conclusive and proves that the infectious material or virus 

 is the same for all of these plants. Sorghum seed of the Early 

 Amber, Sugar Drip, and Japanese Eibbon varieties was sown in a 

 bed at the quarantine greenhouse at Washington, where diseased 

 plants of 17 different varieties of sugar cane were growing. When the 

 sorghum plants were about half grown, practically all of them began 

 to produce mottled leaves and continued to do so until they went to 

 seed. 



The seed was saved from these sorghum plants to determine whether 

 the disease is transmitted to the next generation in the true seed. 1 

 The leaf symptoms in these greenhouse plants were, exactly like the 

 symptoms on sugar-cane leaves. Plants arising from the same batch 

 of seed used in the greenhouse experiment cited above but planted 

 elsewhere and not exposed to the disease did not show the phenomenon 

 but produced healthy leaves of uniform color. The crab-grass, fox- 

 tail, and Panicum came up as volunteer plants in the quarantine 

 greenhouse. Scores of stools of these weeds were allowed to mature 

 for observation and identification. Every plant became infected 

 and exhibited the typical leaf symptoms. Some half dozen other 

 species of wild grasses were present in the greenhouse, but they were 

 not attacked. All of the wild grasses were abundant outside of the 

 greenhouse, but in spite of an assiduous search in the vicinity not 

 a single infected plant could be found. The conclusion to be drawn 

 from these observations is obvious. We are not dealing with similar 

 mosaic diseases of these various graminicolous hosts, the viruses of 

 which are specific for each host, but with one and the same disease. 



The existence of other host plants, especially the common wild 

 grasses, would appear to be one of the most alarming of the recent 

 developments in the problem. It is needless to say that the control 



i This seed was planted in flats. At the present time, three weeks after germination, no sign of the mosaic 

 has appeared. 



