184 Proceedings of Indiana Academy of Science 



prevalent as in previous seasons. However, it was found causing a 50 

 per cent loss in one field in Kosciusko County and Gregory noted one 

 field in Carroll County on August 29 in which there was 10 per cent wilt 

 infection. In a field in Laporte County planted with seed tubers selected 

 for freedom from wilt-infection, about two per cent was found on 

 August 3. Gregory noted the disease in Floyd, Harrison, Hancock, 

 White and Cass counties, and Gaylord noted it in Porter County. A 

 very little wilt was noted in Elkhart County. Gaylord found vascular 

 discoloration very prevalent in the Irish Cobblers grown in Harrison 

 County this season. Kendrick has found that only about 40 per cent of 

 the tubers showing vascular discoloration yield an organism in cultural 

 tests. In the.se isolations, a type of Fusarium predominated and in its 

 temperature relations this form resembled F. oxysporum. Good growth 

 occurred at 16' and 20°, but was best from 24° to 35°, with a rather 

 distinct optimum at 27° to 30° C. 



Gregory reported leaf-roll serious in fields observed in Floyd, Har- 

 rison, and Jasper counties and the disease was also noted in Fulton, 

 Kosciusko, and Elkhart counties. Mosaic may be detected with more 

 certainty than leaf-roll under field conditions and striking cases were 

 observed in Early Ohios in Marion County on May 20, and in Lake 

 County in Early Ohios and Rurals as well. Gregory noted mosaic in 

 Floyd and Dekalb counties. 



During the winter and early spring, Kendrick tested in the green- 

 house, single-eye seed pieces from samples of seed stock sent in from 

 several potato-growing sections in the state in order to ascertain to 

 what extent mosaic and leaf-roll might be present in home-grown seed. 

 Blodgett (5) at Cornell found that these two diseases showed up con- 

 spicuously under greenhouse conditions and this method of analysis is 

 particularly useful in Indiana because the symptoms of these diseases 

 may not be at all clear cut under field conditions. Out of 20 lots of 

 seed tubers from twelve counties, nine lots, representing Hancock, Fulton, 

 Whitley, Floyd, Clark, St. Joseph, Laporte and Lake counties, showed 

 leaf-roll and four of these, both mosaic and leaf-roll. The latter four 

 were from Hancock, Whitley, Clark and Lake counties, and the per- 

 centages of mosaic were low. In addition one lot of Early Ohio seed 

 from Tippecanoe County showed 95 per cent mosaic. The highest per- 

 centages of leaf-roll were in Bull Moose potatoes from Floyd and Clark 

 counties, Carmens from Laporte County, Early Ohios from Tippecanoe 

 County and Rurals from Lake County. These results show that leaf- 

 roll was rather prevalent in the 1920 crop in Indiana and the occur- 

 rence of 81 per cent and 98 per cent leaf-roll in two large lots of Rurals 

 from Lake County and 12 per cent mosaic in one of these lots indicates 

 that leaf-roll and, to a less extent, mosaic are responsible in part for the 

 decline in potato yields in Lake County mentioned in last year's report 

 (17). While leaf-roll may be readily detected under field conditions in 

 the cooler northern states, field row tests at Lafayette and Hammond 

 in 1921 with healthy and leaf-roll seed tubers of the Rural variety 

 showed that it v,-as practically impossible to detect leaf-roll under the 

 field conditions existing in those localities. However, the disease reduced 



