TREE RUST INOCULATION PROBLEMS AND TECHNIQUES : 

 SECTION MODERATOR'S SUMMARY 



Robert F. Patton 

 Department of Plant Pathology, University of Wisconsin, 

 Madison, Wisconsin, U.S.A. 



Inoculations are important in programs of breeding for disease resis- 

 tance because of the need to test materials. We test to see what we have, 

 or to see if we have what we think we have! Here it is as important to 

 provide a broad base of exposure to the pathogen as it is to provide a 

 broad base for initial selections of the suscept. We don't do this as 

 much in artificial inoculations as we should, perhaps. But natural infec- 

 tion plots situated in various areas help in encompassing a wide range of 

 virulence in strains of the pathogen. Our objective in developing screen- 

 ing methods should be to identify the best selections, the best crosses 

 among these, and the best individuals within these progenies. 



Both natural and artificial inoculation methods may be used in 

 screening. With natural inoculations we may have little or no control 

 over the inoculum amount, the environmental conditions, or the time the 

 test may take. Although we should expect natural inoculations to take 

 a long time, to be costly, and often to be unreliable, they nevertheless 

 may have value in aiding interpretation of geographical interactions with 

 climatic or pathogen variation, or of the effects of cultural treatments. 

 Artificial inoculations, on the other hand, can be more efficient and 

 reliable, as was pointed out by Dinus in his comparison between natural 

 and artificial inoculation of slash pine for resistance to fusiform rust. 



The source, amount, and availability of inoculum are major considera- 

 tions in inoculation tests. Collection from wild sources has been 

 depended upon in most tests with Cronartiwn ribicola, C. fusi forme , 

 Melampsora sp., and Peridermiwn pini. The uncertainty inherent in 

 dependence upon wild sources prompted Heimburger to develop a rust garden 

 as a dependable inoculum source. Artificial inoculation also emphasizes 

 the necessity of being certain about identification of the test organism. 

 For example, Klingstrom had to inoculate peony with aeciospores to screen 

 out unwanted host -alternating strains of Peridermiwn pini. Difficulty 

 in identification of Melampsora species complicates the problem of inocu- 

 lation for resistance to M. pinitorqua, and the inability to separate C. 

 fusi forme and C. quercuum in the telial stage necessitates production of 

 inoculum from a known source. 



Inoculum viability is sometimes assumed when it really should be 

 checked. Telia- formation temperature has a pronounced effect on the 

 fertility of telia of C. ribicola. Klingstrom noted that although telia 

 of M. pinitorqua overwinter on aspen leaves, maturation does not occur 

 until spring and premature collection of inoculum must be avoided. Good 

 storage techniques for inoculum of known viability would be a help in 



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