PRODUCTION OF CONIDIA IN GIBBERELLA 

 SAUBINETIP 



By James G. Dickson, Pathologist, Office of Cereal Investigations, Bureau oj Plant 

 Industry, United States Department of Agriculture, and Assistant Professor of Plant 

 Pathology, University of Wisconsin, and HELEN Johann, Assistant Pathologist, Office 

 of Cereal Investigations, Bureau of Plant Industry, United States Department of 

 Agriculture. 



The scab fungus Gihherella saubinetii (Mont.) Sacc, which attacks wheat, 

 com, rye, barley, and oats, has been considered as having a vegetative 

 stage and two spore stages. The conidial and perithecial development 

 terminates the active vegetative period. Strains producing abundant 

 perithecia have been described as developing only a few conidia in 

 scattered, sporodochia-like masses. 



Cultural studies with a large number of strains of G. saubinetii show 

 that in nature, as well as in artificial culture, this species produces conidia 

 at two different periods during its development. Wollenweber ^ suggests 

 this when he states that — 



on steamed potato tuber the conidia form a short-lived pionnotes. The conidia of 

 this pionnotes rapidly swell, separate into cells, germinate, and produce new conidia, 

 which anastomose and form a stroma, while in the other species mentioned the conidia 

 remain perfect, dry out, and are long-lived. 



The first period of conidial production is in connection with the early 

 mycelial growth of the culture, while the second occurs at the termina- 

 tion of ttie vigorous vegetative development. These later conidia are 

 produced in definite sporodochia and are the only conidia generally 

 described for this species. The production of perithecia is the final 

 stage in the development of the culture. 



During the summer of 191 9, single-spore cultures were made by the 

 authors from sporodochial conidia and ascospores taken from stock 

 cultures and from wheat heads, wheat culms, and cornstalks collected 

 in the field. These specimens were obtained from a number of widely 

 separated points in the central and eastern States. Spores from all 

 sources were placed in hanging drops of distilled water and sterile tap 

 water, on poured plates of potato-dextrose agar and soil decoction agar, 

 and on sterile soil. The subsequent development of the fungus was then 

 studied at frequent intervals. 



1 The investigations upon which this paper is based were conducted as a cooperative project between the 

 Office of Cereal Investigations of the Bureau of Plant Industry and the Wisconsin Agricultural Experi- 

 ment Station. 



' Wollenweber, H. W. identification ok species of fosarium occurring on the sweet pot.ito, 

 IPOMOEA batatas. In Jour. Agr. Research, v. 2, no. 4, p. 278. 1914. 



Journal of Agricultural Research, Vol. XIX, No. s 



Washington, D. C. June i, 1920 



U) Key No. G-194 



175343° 20—4 (235) 



