522 Journal of Agricultural Research vol. xx, No. 7 



as described. After the conclusion was reached that the tobacco-wilt 

 Fusarium is related morphologically to Fusarium oxysporum but is not 

 identical with it, several methods of study were undertaken with the 

 hope of furnishing further evidence. These consisted of (1) infection 

 experiments with the tobacco-wilt Fusarium on the potato and certain 

 other plants, (2) comparative cultural studies with Fusarium oxysporum 

 strains secured from other sources, and (3) infection experiments with 

 strains of Fusarium oxysporum from potato upon tobacco. 



Several attempts at producing infection with the Maryland strain 

 of the tobacco-wilt Fusarium on the potato vine failed. Potatoes were 

 grown in artificially infested soil, and in several instances the stems were 

 wounded immediately below the surface of the soil. This, however, is not 

 regarded as conclusive evidence that infection is unobtainable. 



Authentic cultures of Fusarium oxysporum were sought from various 

 recent workers on this species. Cultures of Dr. Wollenweber's strain 

 (No. 207) were received through Dr. W. A. Orton, and also a strain 

 (No. 208) isolated by Dr. H. A. Edson from potatoes. From Minnesota, 

 Bisby's culture No. 3315 and a reisolation from inoculation on potato 

 were secured (j). From the stock cultures in the Department of Plant 

 Pathology at the University of Wisconsin two strains were received, 

 numbered 226 and 227, both apparently originally from Dr. Wollenweber 

 to Link at Nebraska and thence to Goss at Michigan, who brought them 

 to Wisconsin. Finally a culture of MacMillan's strain (8) from potatoes 

 in Colorado, which was sent by MacMillan to the Department of Plant 

 Pathology at Wisconsin, was obtained. None of these cultures was 

 apparently in a good normal growing condition when transferred to my 

 media, as compared with more recently isolated forms on the same 

 media. The growth may be best expressed as "slimy" in nature, as if 

 bacterial contamination had occurred — that is, aerial growth was sparse 

 or absent and a rather thin mycelial growth was formed on the surface 

 of the media only. Many microconidia and some macroconidia were 

 produced. Repeated trials on various media failed to bring about the 

 sporodochial fruiting stage, without which a satisfactory comparison 

 with the septate conidia of the tobacco-wilt Fusarium could not be made. 

 Therefore, the cultures were at first used largely for comparison of cul- 

 tural characteristics on different media, especially on Melilotus stems, 

 cooked rice, oatmeal agar, potato plugs, and potato agar. The various 

 strains of Fusarium oxysporum from the various sources did not behave 

 in a similar manner on the same media, and consequently it was felt that 

 the significance of the cultural comparisons obtained was much reduced. 

 Whether this condition was due to differences in age or condition of the 

 strains or to actual physiological differences inherent in the strains can 

 not be said. 



The following notes were taken on the growth of the tobacco-wilt 

 Fusarium on various media in an early trial. Not much emphasis can be 



