UNITED STATES DEPARTMENT OF AGRICULTURE 



DEPARTMENT BULLETIN No. 1417 



Washington, D. C. 



August, 1926 



OZONIUM ROOT ROT 



GEORGE L PELTIER, formerly Plant Pathologist, C. J. KING, Associate Agronomist 

 Office of Cotton, Rubber, and Other Tropical Plants, Bureau of Plant Industry, and 

 RAYBURN W. SAMSON, Student Assistant, Department of Plant Pathology 

 Nebraska Agricultural Experiment Station 



CONTENTS 



P*ge 

 PART I.— Studies of Ozonium Root Rot in 



Arizona and Texas 1 



Introduction 1 



Distribution of Ozonium omnivorum ... 2 



Symptoms of tbe Disease 3 



Time of First Appearance 3 



Age of Plant Attacked 4 



Development of the Disease 4 



Spread of Root Rot 9 



Pure-Culture Isolation of Ozonium omni- 

 vorum ............... II 



The Fungus 12 



Inoculation Experiments 14 



Data Collected in Previous Years 15 



Page 



PART I.— Studies, etc.— Continued 



Observations during the Summer of 1924 . 17 



Summary of Part I 19 



PART II —The Pathological Anatomy of Ozon- 

 ium Root Rot 20 



Introduction 20 



Material and Methods of Study 20 



The Strand Hyphae 20 



Modes of Entrance 21 



Mechanics of Entrance 21 



Development of the Hyphae in the Tissues 22 



Discussion 23 



Summary of Part II 24 



Literature Cited 27 



WASHINGTON 



GOVERNMENT PRINTING OFFICE 



1926 



