oct.8.r«>4i Blackleg Potato Tuher-Rot under Irrigation 91 



tuber is cut open it reveals a colorless buttery or mushy decay with 

 black streaks, usually on the border line of the diseased and healthy 

 tissues. If exposed to drying the decayed areas may become spongy 

 and very much resemble the texture which is usually observed in Fusa- 

 rium rots (PI. 16, D). In many instances, however, if the decayed region 

 is sufficiently deep to prevent complete drying, sections through such 

 tubers may show an inner layer of active bacterial decay. As is the case 

 with the other forms of blackleg-rot this form, too, may become further 

 invaded with various rot-producing or saprophytic fungi. The writers 

 had under their observation a tuber of this type with a copious growth 

 of Rhizoctonia on the outside all over the diseased area, while soft 

 bacterial decay was still progressing within the tuber even in the dry 

 laboratory atmosphere (PI. 16, C). 



SUMMARY 



(i) An organism isolated from western stem-end rotting potatoes is 

 identical with Bacillus phytophthorus Appel in all the essential charac- 

 ters commonly considered in the determination of bacterial species. 



(2) It is pathogenic to the potato, and inoculations of healthy stems 

 or tubers with pure cultures produce, respectively, a rapid, soft decay 

 of stems or a tuber-rot. 



(3) Blackleg tuber-rot under the field conditions in certain irrigated 

 sections of the West, particularly in pointed-end Netted Gems, takes on 

 a form atypical of the familiar manifestation of this disease in the East. 



(4) The external appearance becomes especially confusing when the 

 affected areas dry up and shrivel in storage, but usually the trouble 

 may be identified by cultural work or by planting diseased tubers under 

 control conditions. 



LITERATURE CITED 

 (i) Appel, Otto. 



1903. UNTERSUCHUNGEN USER DIE SCHWARZBEINIGKEIT UNO DIE DURCH 

 BAKTERIEN HERVORGERUFENE KNOLLENFAULE DER KARTOFFEt. In 

 Arb. K. Biol. Anst. Land. u. Forstw., Bd. 3, Heft 4, p. 364-432, 15 fig., 

 pL 8 (coL). 



(2) Carpenter, C. W. 



1915. some potato tuber-rots caused by species op fusarium. in jout. 

 Agr. Research, v. 5, no. 5, p. 183-210, pL A-B (col.), 14-19. Litera- 

 ture cited, p. 208-209. 



(3) JENNISON, Harry Milliken. 



192 1. BACILLUS ATROSEPTICUS VAN HALL, THE CAUSE OF THE BLACKLEG DIS- 

 EASE OF IRISH POTATOES. (Abstract.) In Phytopathology, v. 11, 

 no. 2, p. 104. 



(4) Morse, W. J. 



1910. CERTAIN DISEASES OF MAINE POTATOES AND THEIR RELATION TO THE 



SEED TRADE. Maine Agr. Exp. Sta. [Misc. Publ.] 375, 12 p. 



