Jan. 3,1921 Fusarium-Wilt of Tobacco 525 



which is very dissimilar to ordinary tobacco. N. glauca has, in fact, 

 been the most susceptible plant to tobacco-wilt with which we have 

 worked. Infection has also been secured upon N. rustica. 



On the basis of this study of the tobacco- wilt Fusarium, it is believed 

 that although Fusarium oxysporum from potato is to be regarded as 

 being able to cause a wilt of tobacco, it is not to be regarded as identi- 

 cal with the tobacco- wilt Fusarium as regards pathogenicity. That 

 certain cultural differences exist has also been indicated. The final 

 justification for placing the tobacco-wilt Fusarium as a variety of F. 

 oxysporum lies in the small but nevertheless significant morphological 

 differences which have been found to exist. These morphological 

 differences are to be found in the somewhat larger conidia but more 

 particularly in the higher percentages of 4- and 5-septate conidia. 



One Fusarium has already been described on tobacco — Fusarium 

 tabacivorum, Delac. — and although this species can not be regarded as 

 authentic, it is thought best not to confuse the nomenclature by deriving 

 the variety name from the specific name of tobacco. Furthermore the 

 tobacco-wilt Fusarium is not limited to Nicotiana tabacum alone but 

 attacks other members of this genus. It is therefore proposed to derive 

 the third member of the trinomial from the generic name of tobacco. 

 Accordingly the name Fusarium oxysporum (Schlecht.) Wr. var. nicotianae, 

 n. var. is proposed. The following description is presented. 



Fusarium oxysporum (Schlecht.) Wr. var. nicotianae, n. var. 



Fusarium nicotianae isolated from wilting tobacco plants {Nicotiana tabacum L.) 

 from Maryland and Ohio agrees quite closely morphologically with Wollenweber's 

 diagnosis of F. oxysporum (Schlecht.) Wr. except in certain details not readily de- 

 termined. Mycelium on most media pure white to a light pinkish tinge, of a rather 

 "powdery" appearance, due to presence of numerous microconidia. Blue and light 

 ochraceous salmon-colored sclerotia formed early on steamed potatoes. No true 

 pionnotes observed. Reduced pionnotes or " pseudopionnotes " obtained. Sporo- 

 dochia produced in abundance on Melilotus stems and on oatmeal agar. These are 

 salmon-colored and when "normal" contain almost entirely 3- to 5-septate conidia, 

 slightly larger than those of F. oxysporum. Three-septate conidia up to 100 per cent 

 34.9 by 4.2 microns (25.0 by 3.7 microns to 45.4 by 4.6 microns). Four-septate up to 

 40 per cent, '39.3 by 4.0 microns (29.6 by 3.7 microns to 46.3 by 4.6 microns). Five- 

 septate up to 18 per cent 44.3 by 4.0 microns (38.9 by 3.7 microns to 51.1 by 4.1 mi- 

 crons). Six-septate very rare. Non-septate conidia in old sporodochia rare (7.1 by 

 2.4 microns). One-septate equally rare (10. 1 by 2.7 microns). Two-septate up to 

 4 per cent (18.5 by 3.7 microns). Non-septate spores from mycelium 8.1 by 3.4 mi- 

 crons (10.2 by 3.7 microns to 3.7 by 2.7 microns). Chlamydospores terminal, inter- 

 calary and conidial, smooth, round, frequently in masses 8.2 microns (6 to 10.2 

 microns). 



Pigment production not so deep as in most descriptions of Fusarium oxysporum. 



Habitat. — Parasitic in fibro-vascular bundles of Nicotiana tabacum in Maryland 

 and Ohio, causing a decided wilting of plants followed by death. Also produces a 

 similar disease of N. glauca and N. rustica by artificial inoculation. 



