Potato Tuber-Rots Caused by Fusarium Spp. 



205 



Table VII. — Percentages of •variously septate normal conidia, average sizes, and limits 

 of size as found in a lo-day-old pionnotes on Melilotus alba and in a 15-day-old 

 cotton pionnotes of Fusarium eumartii. 



lO-DAY-OLD PIONNOTES ON MELILOTUS ALBA 



15-DAY-OLD PIONNOTES ON COTTON 



3 

 4 



5 

 6 



S 



62.9 by 6.1 

 73.2 by 6.6 

 79.9 by 6.6 

 85 by 6.8. . 



56 to 76.5 by 5 to 6.8. 

 51 to 81.6 by 5.9 to 7.2. 

 74.8 to 85 by 6.3 to 6.8. 



The formation of pigment in F. eumartii (PI. A, fig. 6-8) and F. radicicola is much 

 the same as that in F. solani, only more gorgeous. The conidial color fluctuates 

 between brownish white and bright brown; by infiltration of the greenish blue 

 plectenchymatic pigment the conidial mass becomes gray, blue-green, to brown and 

 a dark mixed color. The plectenchymatic stroma is weakly developed or lacking, 

 and therefore the pionnotes lies naked on the substratum. The chlamydospores, 7 to 

 lOM in diameter, agree with those in other species of this section. 



F. eumartii causes a rot of potatoes in experiments, while F. martii is said to be a 

 saprophyte (20, p. 30). This statement was confirmed with F. martii 186 collected 

 in Germany. The new species agrees more closely with Fusisporium solani Martius 

 (8) in the size of conidia than does F. martii. 



F. radicicola and F. eumartii are very closely related to F. martii with respect to 

 average size and septation of normal conidia and occupy the same relative positions 

 on either side of the last-mentioned species as a type. In average measurements 

 the conidia of F. radicicola are approximately 30 per cent shorter and 20 per cent 

 narrower than those of F. martii {sensu strict.), while F. eumartii is larger in about the 

 same proportion. F. radicicola is typically triseptate, F. martii 3- to 4-septate, and 

 the new species 5- to 6-septate. Similar constant varieties of certain other species 

 are known — e. g., of Fusarium solani. 



Habitat. — On decaying tubers of Solanum tuberostim from Pennsylvania and New 

 York. Cause of potato dry-rot and wet-rot. 



4. Fusarium radicicola WoUenw. (21, p. 257-258). 



The conidia of this species are normally triseptate, averaging 30 to 45 by 3.75 to 5^; 

 narrower than in F. solani, sensu strict. (PI. XIV, fig. 3), and shorter and fewer 

 septate than in F. martii and F. eumartii (PI. XIV, fig. 4). The plectenchymatic 

 mycelium, as in the two latter species, is olive colored on potato cylinders, shading to 

 green and brown. Pionnotes on potato cylinders, cotton, and stems of Melilotus alba 

 brownish white to blue and verdigris (PI. A, fig. 6-8). Pigment formation the same 

 as in F. martii and F. eumartii. Chlamydospores as in other species of the section. 



