248 Journal of Agricultural Research voi. xvii, No. « 



GEOGRAPHICAL DISTRIBUTION OF POTATO MOSAIC 



Orton (9, p. 42)^ in 191 1 first observed potato mosaic in a field at 

 Giessen, Germany, where it was very common on some varieties. The fol- 

 lowing year it was found to be prevalent in the potato fields in northern 

 Maine but was not found in Wisconsin, Minnesota, Colorado, and other 

 western states during an extended survey made in 1912 and 1913. In 1913 

 Melchers (<5, p. 15s) observed symptoms of this disease in the greenhouse 

 on potato plants from tubers from New York. More recently Worfley 

 {12) reported it as very prevalent on the Bliss Triumph variety in 

 Bermuda and on Long Island, and Murphy (8) said that the disease 

 occurred to a considerable extent in New Brunswick and to a less extent 

 in western Canada. In 1917 and 1918, collaborators for the Plant 

 Disease Surv^ey reported it from the following states: Alabama, Arkansas, 

 Connecticut, Delaware, Florida, Georgia, Kentucky, Louisiana, Maine, 

 Massachusetts, Michigan, Minnesota, New Hampshire, New York, 

 North Dakota, Ohio, Oregon, Texas, Vermont, Virginia, and Wisconsin. 

 From these reports it is apparent that potato mosaic occurs rather 

 generally throughout the United States. 



Although potato mosaic, named as such, has been reported for the 

 first time within the last decade, the following statement made by 

 Johnson (4) before the middle of the nineteenth century is of interest. 

 In a description of a potato disease which seems to have somewhat 

 resembled mosaic he says : 



The stem is tinbranched, brownish green or mottled, and here and there sprinkled 

 with rusty spots, which penetrate to the pith, so that it is not white but rust colored 

 or sometimes black. The upper surface of the leaves is not as smooth as is usual in 

 the case with potato leaves but rough, ivrinkled, or curled. The leaves are far more 

 sessile than usual, and are not of a uniform brownish or dark green color, but spotted? 



Johnson further says that this trouble can be produced by repeated 

 removal of the sprouts before planting. 



EFFECTS UPON YIELD 



The yield from affected plants is less than that from healthy vines of 

 the same variety. Orton {9, p. 42) as the result of an experiment with 

 Green Mountain potatoes in northern Maine reports a difiference in yield 

 of 22 per cent between 80 healthy and 80 diseased hills. Wortley {12) 

 states that 200 healthy Bliss Triumph hills yielded more than twice as 

 much as 200 diseased hills of the same variety and that mosaic of potatoes 

 in Bermuda frequently causes a reduction in yield of from 10 to 75 per 

 cent. Murphy {8) compared 682 diseased Green Mountain hills, scat- 

 tered over II plots, with the same number of healthy hills growing 

 adjacent to the diseased hills. He found the yield of the former to be 



' Reference is made by ntunber (italic) to " Literature cited," p. 272-273. 

 ^ Italics in this quotation are supplied by the writers. 



