I certify that I have read this study and that in ray opinion it 

 conforms to acceptible standards of scholarly presentation and is fully 

 adequate, in scope and quality, as a dissertation for the degree of 

 Doctor of Philosophy. . , — - ; ; -, 



David J. Mitchell " " " — 



Chairman 



Associate Professor of Plant 



Pathology 



I certify that I have read this study and that in my opinion it 



conforms to acceptible standards of scholarly presentation and is fully 



adequate, in scope and quality, as a dissertation for the degree of 



Doctor of Philosophy. . 



ft* 



jxL % : JcJ?,yrr^' 



Lee F. Jackson 



Assistant Professor of Plant 



Pathology 



I certify that I have read this study and that in my opinion it 

 conforms to acceptible standards of scholarly presentation and is fully 

 adequate, in scope and quality, as a dissertation for the degree of 

 Doctor of Philosophy. , r 



Ronald M. Sonoda 



Associate Professor of Plant 



Pathology 



I certify that I have read this study and that in my opinion it 

 conforms to acceptible standards of scholarly presentation and is fully 

 adequate, in scope and quality, as a dissertation for /the- degree of 

 Doctor of Philosophy. /(/ - /; /]L ' -'1/ 



David H. lubbell 

 Professor of Soil Science 



This dissertation was submitted to the Graduate Faculty of the College 

 of Agriculture and to the Graduate Council and was accepted as partial 

 fulfillment of the requirements for the degree of Doctor of Philosophy, 



-\ 



June, 1980 



y>4 ^ cJTv, 



^o 



Deahi College of Agriculture 



Dean, Graduate School 



