A BRIEF CONSPECTUS OF PATHOLOGY AND GENETICS OF 

 CRONARTIUM RIBICOLA AS RELATED TO RESISTANCE 1 



Robert F. Patton 

 Department of Plant Pathology > University of Wisconsin 

 Madison, Wisconsin^ U.S.A. 



ABSTRACT 



Infection of the pine needle by Cronartium ribicola results from 

 the formation of infection structures in the substomatal chamber. 

 The infection capability of a spore may be the result of an 

 interaction of inherited tendency toward a specific type of 

 germination with microclimatic influences on the host substrate. 

 Although germination of basidiospores may occur within a rela- 

 tively wide range of environmental conditions, the formation of 

 infection structures and consequent infection of the pine are 

 apparently subject to additional subtle factors such as fluc- 

 tuating temperatures and a contact or chemical stimuli, or both, 

 in the stoma of the pine needle. 



Evaluation of clonal or progeny inoculation tests must include 

 consideration of factors affecting host susceptibility, including 

 age of stock, its genetic resistance or susceptibility, vigor of 

 the trees, and maturation of tissues at the infection court. 



Resistance in the pine host is expressed against initial infection 

 in the needle, and against invasion and establishment of the 

 fungus in bark tissues. Bark resistance is expressed by wound 

 periderm formation or a hypersensitivity reaction. In the 

 needle, stomatal influences play a role in the incidence of 

 infection. Wax plugs appear to reduce the number of chances 

 for infection to occur, especially in secondary needles, and 

 may be one influence of age of stock, but probably this is not 

 a major mechanism of inherent resistance. Inhibition of 

 vesicle formation is another aspect of stomatal influence and 

 is one way in which resistance to needle infection is expressed. 



Inheritance of resistance seems to be largely through poly- 

 genes with additive effects. Information is just beginning to 

 accrue on the numbers and kinds of genes associated with 

 specific resistance reactions. 



It is not yet known with certainty whether the fungus is homo- 

 thallic or heterothallic, and if pathogenic races for pine 

 exist . 



* Published with the approval of the Director, Wisconsin Agricultural 

 Experiment Station. Supported in part by U.S. Forest Service Grant No. 1 

 (4000) and National Science Foundation Grant GB-3297. 



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