A LITERATURE REVIEW OF INOCULATION TECHNIQUES USED 

 IN STUDIES OF FUSIFORM RUST 



Robert A. Schmidt 

 School of Forestry 3 University of Florida 

 Gainesville, Florida, U.S.A. 



ABSTRACT 



Inoculation techniques used in studies of fusiform rust 

 (Cronartium fusi forme) are summarized, covering both mass 

 inoculations and individual tree inoculations. Purposes, 

 results, advantages, and disadvantages of each technique are 

 listed. Infection processes and conditioning factors which 

 affect successful inoculations are discussed, as are inherent 

 advantages and disadvantages of natural and artificial inocu- 

 lations. A scheme utilizing both types for screening pine for 

 fusiform rust resistance is outlined. Some consideration is 

 given to the evaluation of rust resistance and also to areas 

 in need of further investigation. 



INTRODUCTION 



Although the inoculation of pine with sporidia of Cronartium fusiforme 

 Hedge, and Hunt ex Cumm. is only one of the many interactions in the 

 fusiform rust disease of southern pine, it is, perhaps, the most important 

 to researchers interested in the identification of rust resistant trees. 

 In order to identify resistant plants, one must create an epidemic and 

 this necessitates a successful inoculation technique. It does not suffice 

 to use only a technique which consistently produces diseased plants. It 

 is necessary to perfect a technique which approximates inoculation under 

 natural conditions. A technique which negates useful field resistance in 

 the test population may have limited application. For example, a method 

 which injects sporidia into the stem bypasses all foliar resistance 

 mechanisms, as well as mechanisms for resistance to penetration of the 

 stem. However, these unnatural inoculation techniques may have utility 

 in studies of the mode of resistance or other disease phenomena. 



Inoculation is most often defined as the arrival of the inoculum at 

 the infection court. In the case of airborne fungus spores, e.g., sporidia 

 of C. fusiforme , inoculation is in effect the process of deposition. 

 Although subsequent germination and penetration are implied in successful 

 inoculations, they are separate processes. Likewise, colonization and 

 symptom development are separate entities; conventionally the latter 

 signals the end of the incubation period. For the most part, the success 

 of inoculation techniques in fusiform rust resistance research is judged 

 by the presence of foliar lesions or stem galls. This involves (1) germi- 

 nation of telia (production of sporidia) , (2) deposition of sporidia onto 



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