A THIRD BIOLOGIC FORM OF PUCCINIA GRAMINIS ON 



WHEAT ^ 



[PRELIMINARY PAPER 



By M. N. LevinE, Field Assistant, Office of Cereal Investigations, Bureau of Plant 

 Industry, United States Department of Agriculture, and E. C. Stakman, Head of 

 the Section of Plant Pathology, Department of Agriculture, University of Minnesota 



COOPERATIVE INVESTIGATIONS BETWEEN THE AGRICULTURAL EXPERIMENT 

 STATION OF THE UNIVERSITY OF MINNESOTA AND THE BUREAU OF PLANT 

 INDUSTRY OF THE UNITED STATES DEPARTMENT OF AGRICULTURE = 



Two biologic forms of stemrust have been known to occur on wheat. 

 PiACcinia graminis tritici Erikss. and Henn. was the only one recognized 

 until recently, when P. graminis tritici-compacti Stak. and Piem. was 

 discovered.^ 



Stemrust collected on clumps of volunteer wheat at Stillwater, Okla., 

 October i8, 191 7, was found to be different parasitically from both P. 

 graminis tritici and P. graminis tritici-compacti. Immediately after 

 collection it was sent to University Fann, St. Paul, Minn., where inocu- 

 lations were begun to determine its identity. It was cultured for several 

 generations on Brown Gloria club wheat, Haynes bluestem (Minn. 169), 

 and Manchuria barley (Minn. 105), during which time its identity was 

 in doubt. Spore measurements made during the same time appeared to 

 indicate that the rust was neither P. graminis tritici nor P. graminis 

 tritici-compacti. 



The discovery of P. graminis tritici-compacti and subsequent work 

 with it showed clearly the value of using differential hosts to distinguish 

 between different biologic forms. It has been shown previously ^ that 

 two or more biologic forms could infect many grasses and some cereals 

 equally well but that their action on at least one of the common cereals — 

 wheat, barley, oats, and rye — was sufficiently different to make their 

 determination simple. For instance, P. graminis tritici and P. graminis 

 secalis attack many grasses and barley equally well; oats are almost 

 immune from both ; but the tritici foim attacks rye only weakly and attacks 

 common wheats heavily, while the secalis form attacks rye heavily and 



• The writers are under obligation to Dr. Charles Drechsler, Field Assistant, Office of Cereal Investiga- 

 tions, Bureau of Plant Industry, U. S. Department of Agriculture, for participating in the collection of the 

 original material: to Mr. G. R. Hoerner, Assistant in Plant Pathology, Minnesota Agricultural Experiment 

 Station, for the preliminary inoculations: and to Mr. J. G. Leach, Shevlin FeUow, University of Minnesota, 

 for valuable suggestions and for many of the data on the differential hosts for P. graminis tritici and P. 

 graminis irilici-compadi . 



' PubUshed, with the approval of the Director, as Paper 121 of the Journal series of the Minnesota 

 Agricultural Experiment Station. 



5 Stakman, E. C, and Piemeisel, F. J. a new strain of puconia graminis. In Phytopathology, 

 V. 7, no. I, p. 73. 191 7. 



•* Stakman, E. C, and Piemeisei,, F. J. biologic forms of puconia graminis on cereals and 

 GRASSES. In Jour. Agr. Research, v. 10, no. 9, p. 429-496, pi. 53-59. i9i7- Literature cited, p. 493-495- 



Journal of Agricultural Research, Vol. XIH, No. 12 



Washington, D. C. June 17, 1918 



oj (651) Key No. Mirm.-30 



66114°— 18 4 



