502 a. G. KAIS AND G. A. SNOW 



DISCUSSION 



From their different effects on the 5 species of pine, we believe 

 that these three geographic sources of C. querouum are distinct pathogenic 

 races. The Wisconsin source was pathogenic to slash and jack pine; the 

 North Carolina source was pathogenic to loblolly and sand pine; and the 

 Mississippi source was pathogenic to slash, loblolly, shortleaf, and, to 

 a lesser extent, jack pine. It is probable that further studies would 

 reveal other pathogenic races of C. qierouum. Recently, pathogenic 

 variability has also been observed in C. fusi forme (Snow, Powers, and 

 Kais, 1969). 



This study has generally confirmed the belief that plants infected 

 with C. fusi forme tend to form fusiform galls and plants infected with 

 C. querouum tend to form globose galls. It is difficult to account 

 for the formation of both types of galls on loblolly and sand pine 

 inoculated with the one North Carolina isolate of C. querouum. The 

 plant response may be attributable to variability of the isolate or to 

 variability within the two species of pine. Variability within the 

 isolate may be the better explanation, since galls resulting from all 

 other isolate-pine inoculations were uniform in shape. 



Besides gall shape, host plant susceptibility definitely varies 

 between C. fusi forme and C. querouum. While shortleaf, jack, and sand 

 pine were all very resistant to C. fusi forme , they were susceptible in 

 some degree to one or more of the isolates of C. querouum. When data 

 for all our C. querouum isolates are combined, they agree with past 

 reports (Hedgcock and Siggers , 1949) in showing that C. querouum can 

 infect slash, loblolly, shortleaf, jack, and sand pine. But when the 

 geographic isolates are evaluated individually, it becomes apparent that 

 they cause different reactions on the hosts. 



Two types of recovery from infection were observed: formation of 

 primary symptoms (purple spots) without subsequent gall development, and 

 the disappearance of definite galls on infected plants. All of the 

 inoculated plants developed primary symptoms, an indication that the 

 inoculation technique was very efficient. The recovery of plants from 

 fusiform rust infection has been previously reported (Snow, Jewell, and 

 Eleuterius, 1963) . 



The findings of this study suggest two courses of action. First, 

 criteria should be established for differentiating races of these rusts. 

 Second, tree breeders and geneticists should be prepared to cope with 

 the problems arising from pathogenic variability in Cronartium species. 



LITERATURE CITED 



Arthur, J. C. 1962. Manual of the rusts in the United States and Canada. 

 Hafner Publishing Co., New York. 438 p. 



Gooding, G. V., Jr., and H. R. Powers, Jr. 1965. Serological comparison 

 of Cronartium fusi forme s C. quercuum 3 and C. ribioola by immuno- 

 diffusion tests. Phytopathology 55: 670-674. 



Hedgcock, C. G., and P. V. Siggers. 1949. A comparison of the pine-oak 

 rusts. U. S. Dep. Agr. Tech. Bull. 978. 30 p. 



Jewell, F. F., and N. M. Walker. 1965. Normal and abnormal mycelial 



characteristics of Cronartium querouum in shortleaf pine. Phytopathology 

 55: 1325-1327. 



