2o6 Journal of Agricultural Research voi. v, no. s 



Habitat. — On partly decayed tubers and roots of plants. Cause of potato dry-rot 

 and jelly-end rot. Identified from the following: Ipomoea batatas (collected by 

 Mr. L. L. Harter); Ahisa sapienium (collected by Mr. S. F. Ashby, Jamaica, Porto 

 Rico); Cucumis sativus (collected by Mr. F. V. Rand, West Haven, Conn.); soil 

 (collected by Mr. F. C. Werkenthin, Austin, Tex.). 



B. SECTION ELEGANS 



[Species in this section are F. oxysporum Schlecht., F. hyperoxysporum WoUenw., F. vasin/edum Atk., 

 F. trackeiphilum Sm., F. nheum Sna., F. lycopersici Sacc, F. conglutinans Wollenw., F. redolens Wol- 

 lenw.. F. OTthoceras App. and Wollenw., F. orthoceras, var. triseptalum WoUenw., F. balatatis Wollenw.) 



1. Fusarium oxysponun Schlecht. (20, p. 28). 



2. Fusarium hyperoxysporum Wollenw. (21, p. 268). 



F. oxysporum (PI. XIV, fig. i) is not sharply differentiated morphologically from 

 several species of this section — ^namely, F. hyperoxysporum, F. vasinfectum, F. trackei- 

 philum, F. lycopersici, and F. niveum. F. hyperoxysporum. forms a perfect pionnotes 

 in contrast to the reduced pionnotes in F. oxysporum (PI. A, fig. 1-5). According to 

 Harter and Field (4, p. 296), it is different biologically in that it causes a stem-rot of 

 Ipomoea batatas and is not infectious on young plants of Solatium tuberosum, while 

 F. oxysporum causes a wilt of the latter host but does not attack the former (2 1 , p. 26S). 

 Both develop a lilac odor on starchy media. However, this character is of doubtful 

 specific value since non-odor-forming strains of F. oxysporum, F. hyperoxysporum, and 

 F. -vasinfectum have been isolated, and some of the odor-forming strains temporarily 

 lose this property in cultiu-e. 



F. iracheiphilum, the cause of a w-ilt of species of Vigna, is without pionnotes and 

 odor. F. vasinfectum, the cause of a wilt of cotton, develops a perfect pionnotes of an 

 ocherous-salmon color; on potato cylinders in subdued light this color becomes slightly 

 purple. Typically a strong lilac odor is present on starchy media. A non-odor- 

 forming strain was designated F. vasinfectum, var. inodoratum, by WoUenweber (20, 

 p. 29). F. lycopersici, the cause of a u'ilt of Solanum lycopersicum, differs from F. 

 oxysporum in having conidia of a little larger average size and produces colorless 

 sclerotial plectenchymatic masses in contrast to the bluish masses of this sort in 

 F. oxysporum, etc. No odor is developed. F. niveum, to which the wilt of species of 

 Citrullus is attributed, differs from F. lycopersici in forming blue sclerotial bodies on 

 potato cylinders; from F. oxysporum in having, larger conidia and no odor. 



It is possible to determine the six above-mentioned species by morphological 

 characters alone. Although a knowledge of the host of the particular species to be 

 determined is not necessary, such information greatly facilitates the work. In spite 

 of the fact that each of these forms seems to cause a wilt on one particular host, it 

 should be pointed out that too much dependence on the value of the host in descrip- 

 tions of species has led to the present confusion in the nomenclature of the form genus 

 Fusarium. 



A species of Fusarium causing a field soft-rot of Irish potatoes in Mississippi (PI. 

 XV, fig. I, 2) was morphologically identical with F. oxysporum (PI. XIV, fig. i), but 

 developed a perfect pionnotes on potato cylinders (PI. A, fig. 4); thus, it must be 

 identical with F. hyperoxysporum, the cause of stem-rot of the sweet potato. Inocu- 

 lation with F. hyperoxysporum isolated by Harter and Field from the latter host re- 

 sulted in complete destruction of the tubers (see No. 3399 and reisolation of same, No. 

 3489, p. 192), indicating the truth of the hypothesis. 



Further cross-inoculation work carefully controlled by morphological 

 studies should demonstrate whether all of the above-mentioned species 

 of this section are biologically distinct; whether, for example, F. hyper- 

 oxysporum differs sufficiently from F. oxysporum, on the one hand, and 

 F. vasinfectum, on the other, to be entitled to the rank of species. 



