Oct. 8,1921 Soybean Mosaic 113 



On January 26, twenty-five plants were inoculated by pricking with a 

 needle at the nodes and rubbing the wounded areas with cotton soaked 

 in the juice from crushed mosaic leaves. Eight plants used as controls 

 were similarly treated, except that sterile water was substituted for 

 the mosaic virus. Because of the unfavorable greenhouse conditions 

 the plants made slow growth during the winter, so that the mosaic 

 symptoms were very slow in developing. On March 5 two plants 

 showed mosaic mottling on the young leaves. On March 25 two more 

 showed mosaic, and on April 7 seven out of the 25 plants had developed 

 the disease. The controls developed no mosaic. 



A number of inoculations were made March 2. In one series crushed 

 mosaic tissue was inserted into slits made with a scalpel near the grow- 

 ing points and on the petioles. On March 15 two of the seven plants 

 thus inoculated showed mosaic symptoms on the young leaves, and on 

 April 7 five had developed mosaic. 



In a second series of inoculations made the same date by cutting off 

 one leaf at each node and smearing these wounded surfaces with crushed 

 mosaic tissue, three out of eight plants showed mosaic symptoms on 

 the new leaves March 15, or 13 days after inoculation, and on April 7 

 six plants had developed mosaic. 



In a third series five plants were inoculated by a combination of the 

 two methods above described. Thirteen days later three showed mosaic 

 mottling, and by April 7, or 37 days after inoculation, four had developed 

 the disease. 



In a fourth series, five plants w^e inoculated by rubbing the under 

 surfaces of the leaves with slightly crushed mosaic leaves forcibly enough 

 to cause slight abrasions. On March 15, four of these plants showed 

 the disease, and on April 7 all showed typical mosaic. 



None of the five control plants inoculated by one or the other of these 

 methods without the application of mosaic tissue developed mosaic. 

 At no time was there any spread of the disease in the greenhouse. 



In these inoculations the symptoms became evident only on the 

 young leaflets. These in some cases developed distinct mottling, and 

 in other cases they exhibited a slight degree of etiolation and the char- 

 acteristic downward, longitudinal rolling. The incubation period 

 under the conditions of this test was 13 days. 



Preliminary cross inoculations to garden beans and cowpeas have 

 given negative results. Further tests are being made. 



Soybeans, therefore, are subject to a destructive mosaic disease which 

 greatly reduces the yield of affected plants. The disease is transmis- 

 sible from plant to plant and also is seed-borne. 



