324 Journal of Agricultural Research voi. xix.no. 7 



INOCULATIONS FROM ONE VARIETY TO ANOTHER IN THE OPEN 



Early Repeated Application of Juice 



In order to determine whether the juice of a mosaic plant of one 

 variety could induce the disease when introduced into a plant of a 

 different variety of potato, intervarietal inoculations were made under 

 open field conditions. The procedure of inoculation practiced in this 

 connection was similar to that followed with the inoculations indicated 

 in Table TV. In this experiment the control plants always were treated 

 before mosaic juice was used, and a separate set of unstruments was em- 

 ployed for each distinct variety and for juice from each source. Green 

 Mountain, Bliss Triumph, and Irish Cobbler varieties were used. 

 These were subjected to four successive treatments at weekly intervals, 

 as indicated in Table V. 



The results given in Table V show that mosaic juice from one variety 

 of potato may produce the disease when introduced into the plants of 

 another variety. In these inoculations the effect upon the treated plants 

 was fully as severe as that obtained when juice was introduced into 

 plants of the same variety, as explained in connection with Table IV. 

 In fact, in many cases the inoculated plants behaved like those in the 

 late or bad stage of the disease. (Pi. 53-55.) 



From Table V it is apparent that a large percentage of the plants had 

 become infected in 191 8. In view of the fact that such tuber units did 

 not show the mosaic mottling at the time of the first inoculation, when 

 the plants varied in height from 2 to 8 inches, it was impossible to restrict 

 inoculation to healthy units. However, in this connection it is inter- 

 esting to note that the hills infected in 191 8 and inoculated in this ex- 

 periment showed the disease like the plants in the bad' stage whenever 

 the uninoculated control hills in the same tuber units showed but slight 

 or medium infection, so that apparently inoculation with juice increased 

 the severity of the infection which had resulted from transmission in 

 the field the previous season. 



Since a considerable number of the plants in this experiment appar- 

 ently had become infected in 191 8, the evident objection might be offered 

 that, in the course of the inoculation, infectious juice was carried from 

 diseased to healthy plants of the same variety and thus caused infection. 

 This objection can be eliminated. Inoculations always were commenced 

 at the same end of the plot and row, and hence the respective tuber units 

 were operated upon in the same consecutive order. In all cases, with 

 the exception of Bliss Triumph inoculations with mosaic Irish Cobbler 

 juices, the inoculated hills of the tuber unit treated first in each of the 

 different varieties became diseased while the uninoculated hills of this 

 unit remained healthy during the course of the experiment. Further- 

 more, a number of mosaic tuber units, apparently infected in 191 8, were 

 among the controls, or the units treated with juice from healthy plants. 



