TRANSMISSION OF THE MOSAIC DISEASE OF IRISH 



POTATOES* 



By E. S. ScHULTz, Pathologist, Office of Cotton, Truck, and Forage Crop Disease Investi- 

 gations, Bureau of Plant Industry, United States Department' of Agriculture, and 

 Donald Folsom, Assistant Plant Pathologist, Maine Agricultural Experiment 

 Station 



INTRODUCTION 



In a previous publication ^ evidence was presented that mosaic of the 

 Irish potato is a transmissible disease. In view of the fact that a large 

 number of the experiments establishing the transmissibility of this 

 disease were conducted in the greenhouse, it was considered advisable to 

 confirm those results under field conditions. Furthermore, in connection 

 with these experiments in the field additional contributions to our 

 knowledge of mosaic of potatoes were secured. It will be the purpose 

 of the following pages to present these results, which, unless otherwise 

 indicated, have been obtained in northern Maine. 



TUBER TRANSMISSION 

 MODIFICATION OP SEVERITY FROM YEAR TO YEAR 



It is well known ^ that mosaic of Irish potatoes (Solanum tuberosum 

 L) is transmitted from one generation of plants to another through the 

 tubers. It has been shown ^ that there may be great variation in the 

 severity of the symptoms shown by the progeny of a given stock, strain, 

 hill, or tuber. 



Progeny of hills which appeared healthy during 191 8 while growing 

 in plots w^hich contained some mosaic hills and which were situated near 

 all-mosaic plots were grown and observed during the season of 191 9. 

 Most were of the Green Mountain, some of the Bliss Triumph, and a few 

 of the Irish Cobbler variety. Each of the various lots contained some 

 mosaic hills, the percentage varying from 12 to 76. Altogether there 

 were over 4,000 hills, of which 1,200, or 30 per cent, were mosaic. In 

 view both of results reported previously ^ and of the abundance of 

 aphids in 191 8, it seems that these mosaic hills represent cases of tuber 

 transmission following aphid transmission occurring so late in the season 

 of 1 91 8 that no symptoms were apparent. The severity of the symptoms 



' Conducted as one of the cooperative projects between the OflBce of Cotton, Truck, and Forage Crop 

 Disease Investigations of the Bureau of Plant Industry, United States Department of Agriculture, and the 

 Department of Plant Pathology of the Maine Agricultural Experiment Station. 



2 ScHXJLTz, E. S., Folsom, Donald, Hildebrjvndt, F. JI., and Hawkins, Lon A. investigations on 

 THE MOSAIC DISEASE OF THE IRISH POTATO. In Jour. Agr. Research, v. 17, no. 6, p. 247-273, pi. A-B, 25-30. 

 1919. Literature cited, p. 272-273. 



Journal of Agricultural Research, Vol. XIX, No. 7 



Washington, D. C. July i, 1920 



un Key No. G-197 



(315) 



