TESTING FOR PATHOGENIC VARIABILITY WITHIN 

 CRONARTIUM FUSIFORME AND C. QUERCUUM 



H. R. Powers, Jr. 

 Southeastern Forest Experiment Station, Forest Service, 

 U. S. Department of Agriculture 3 Athens, Georgia, U.S. A, 



.ABSTRACT 



The pathogenic variability of Cronartium fusiforme and C. 

 querouum was investigated using aeciospore collections from 

 different pine hosts and different geographic locations. Each 

 collection was used to inoculate northern red oaks. Telia 

 formed on these oak leaves were used to inoculate 4- to 6-week- 

 old seedlings of 16 species of hard pines. Between 300 and 

 400 seedlings of each pine species were inoculated with each 

 rust collection. After growing for 7 to 9 months in a green- 

 house, these seedlings were examined for stem galls. 



Four collections of C. fusiforme produced relatively uniform 

 infection response on the 16 pine species. Infection averaged 

 almost 80 percent on very susceptible species, such as Jefferey, 

 Monterey, South Florida slash, and ponderosa pine. Loblolly, 

 slash, and Austrian pine had intermediate infection percentages, 

 ranging from 35 to 50 percent. A large number of species were 

 highly resistant, including such southern species as pond, sand, 

 and spruce pine. 



The two collections of C. querouum, one from jack and one from 

 Virginia pine, produced contrasting infection results on several 

 of the pine species tested. The Virginia pine collection pro- 

 duced galls on 43 percent of the Virginia pine seedlings and 

 none on the jack pine, and the jack pine collection produced 

 70 percent infection on jack pine but none on Virginia pine. 

 This demonstrated the existence of distinct physiologic races 

 of this organism. 



Breeding for rust resistance requires an understanding of the patho- 

 genic capabilities of the causal fungi. In the South, the most important 

 pathogen of planted slash [Finus elliottii var. elliottii Engelm.) and 

 loblolly (Finus taeda L.) pine is the fusiform rust fungus Cronartium 

 fusiforme Hedge, and Hunt ex Cumm. This fungus, which produces spindle- 

 shaped galls on branches and stems, causes extensive damage to nursery 

 seedlings, young plantations, and seed orchards (Verrall, 1958; Campbell, 

 Darby, and Barber, 1962). Another pine-oak rust fungus, the eastern gall 

 rust [C. querouum (Berk.) Miyabe ex Shirai) , also occurs in this same 

 geographic area because the range of one of its primary hosts, shortleaf 

 pine [Finus eohinata Mill.), extends southward almost to the Gulf of 



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