PATHOLOGY AND GENETICS OF TREE RUST RESISTANCE 

 MODERATOR'S SUMMARY 



P. Schutt 

 Forstzot^.isz^.is Institut 3 MGnehen , Z-ermany 



We have just terminated the Friday morning panel, covering the 

 pathology and genetics of tree rust resistance. During the past few hours 

 several authorities presented excellent summarizing reports about differ- 

 ent sections of our basic knowledge in this field. 



Now, during the last 10 minutes I am expected to give some kind of a 

 final summarizing outlook. This is a hard and almost impracticable task, 

 for nobody wants to have a summary of several summaries. Consequently I 

 would prefer to go a different way. 



Having completed an inventory of the known information, we know just 

 where we stand. Moreover we can state that much progress has occurred, 

 especially during the last 5 years. But in spite of all that, we have 

 good reason to face the unsolved problems of our field, for many of the 

 most important and difficult questions remain unanswered. Let me tell 

 you more concretely what I mean: 



1. Infection biology, including mechanisms of resistance . --In 

 several rust diseases of forest trees like Zro'^arzi-jr. ribi3cZa 3 -y.sZarzscra 



toraua 3 :r 'Ferider nn rl-t/T r . ipir.i, up to now the process of infection is at 

 least only partly known. As long as pathologists do not know how the 

 fungus finds its way into the host and how it grows within the host tissues, 

 it is difficult to understand much about resistance mechanisms. And if 

 we ignore the existence of different mechanisms of resistance, we sooner 

 or later are led to something like an "everything or nothing" standpoint. 

 Perhaps we already have taken some steps in this direction, for those 

 forms of resistance like tolerance or recovery ability, which in my 

 opinion may be of special importance for rusts on forest trees , were 

 seldom mentioned here. So I would like to stress that increased activi- 

 ties and more investigations concerning the basic questions of infection 

 and resistance biology are very much needed. 



2. Problems of pathogen identification and differentiation . --We now 

 have good evidence that racial differentiation exists within the rust 

 fungi Zronaptiim qusreuum^ Cronartium ribioola and Peridsimiian p :'•:.'. 

 There is no doubt that these findings increase the tree-breeders' risk. 

 So, further investigations about the size of race spectra and their geo- 

 graphical distribution are evident. Although it appears different the 

 situation in poplar rusts in general is similar to that in pine rusts. 



In both cases pathologists have difficulties in identifying the pathogen, 

 here the species, there the race. Again, however, in order to control the 

 rust we first must know practically every detail about its biology and 

 pathogenicity. Otherwise drawbacks cannot be avoided. Consequently 

 - Authorities for Latin binomials are given in the subject index. 



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