UNITED STATES DEPARTMENT OF AGRICULTURE 



DEPARTMENT BULLETIN No. 1417 



Washington, D. C. 



August, 1926 



OZONIUM ROOT ROT 



By Geokge L. Peltier, formerly Plant Pathologist, 1 C. J. King, Associate Agron- 

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

 Industry, and Rayburx W. Samson, Student Assistant, Department of Plant 

 Pathology, Nebraska Agricultural Experiment Station 2 



CONTENTS 



Page 



Part I. — Studies of Ozoniuni root rot 



in Arizona and Texas 1 



Introduction 1 



Distribution of Ozonium omniv- 



orum 2 



Symptoms of the disease 



Time of firsts appearance '■'< 



Age of plant attacked 4 



Development of the disease 4 



Spread of root rot 9 



Pure-culture isolation of Ozo- 

 nium ornniyorum, 11 



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 Ozonium root rot 20 



Introduction 20 



Material and methods of studv_ 20 



The strand hyphse 20 



Modes of entrance 21 



Mechanics of entrance 21 



Development of the hyphas in 



the tissues 22 



Discussion 23 



Summary of Part II 24 



Literature cited 27 



Pakt I.— STUDIES OF OZONIUM ROOT ROT IN ARIZONA 



AND TEXAS 



By George L. Peltier and C. J. King 



INTRODUCTION 



Root rot caused by the fungus Ozonium ornnivorum Shear is a 

 disease occurring in certain sections of the Southwest. It attacks 

 a great variety of plants, but primarily affects cotton, alfalfa, and 

 fruit and ornamental trees. In spite of the fact that root rot has 



1 PIa Ptk Pathologist. Nebraska Agricultural Experiment Station ; Plant Pathologist. Bu- 

 reau of Plant Industry, from June 14 to Sept. 13. 1924. 



2 The senior writer wishes to acknowledge the assistance of George T. Ratliffe associate 

 agronomist. Office of Western Irrigation Agriculture, Bureau of Plant Industry, who 

 placed at his disposal all the facilities of the United States San Antonio Field Station, 

 San Antonio, Tex., including all the data and photographs collected since 1916 on 

 Ozenium root rot. 



The writers also wish to thank H. F. Loomis, junior agronomist, Office of Cotton, 

 Rubber, and Other Tropical Plants, Bureau of Plant Industry, for some of the photo- 

 graphs reproduced in this bulletin. 



92792—26 1 -,, 



