HOST RESPONSE OF PINES TO VARIOUS ISOLATES OF 

 CRONARTIUM QUERCUUM AND CRONARTIUM FUSIFORME 



A. G. Kais and G. A. Snow 



Southern Forest Experiment Station, U. S. Department 



of Agriculture, Forest Service 



Gulfport, Mississippi, U.S.A. 



ABSTRACT 



When pines of five species were uniformly inoculated with 

 isolates of Cronartium quereuum and C. fusi forme , differences 

 in susceptibility of the trees to three geographic sources of 

 C. quereuum were observed during the first year. Pinus elliottii 

 and P. banksiana were susceptible to Wisconsin isolates; P. 

 taeda and P. elausa to North Carolina isolates; and P. elliottii, 

 P. taeda, P. eehinata, and P. banksiana to Mississippi isolates. 

 In the C. fusiforme inoculations, the hosts responded similarly 

 to four isolates from various Mississippi sources. Gall shape 

 and recovery from symptoms also varied among geographic sources 

 of C. quereuum. C. quereuum could be distinguished from C. 

 fusiforme by gall shape and by host range. These results 

 establish that races of C. quereuum exist. They also confirm 

 previous research indicating that response of the pine host 

 can be used to distinguish the two species of Cronartium. 



The geographic range of Cronartium fusiforme Hedge. $ Hunt ex Cumm. 

 is overlapped almost completely by the range of Cronartium quereuum 

 (Berk.) Miyabe ex Shirai. The former of these two pine-oak rust fungi 

 is the most serious pest of southern pines, while the latter is relatively 

 minor in the South. Morphologically the two species are considered to be 

 identical. Although both serological (Gooding and Power, 1965) and 

 histological (Jewell and Walker, 1965) differences have been observed, 

 the best distinction is still considered to be gall shape (Peterson, 

 1967). Following Hedgcock and Siggers (1949), galls of C. quereuum are 

 regarded as primarily spheroid, while C. fusiforme galls are always 

 elongated and usually fusiform. The only other distinguishing feature 

 is the species of pine attacked. Some southern pines are susceptible to 

 both fungi, some to only one, and some to neither (Arthur, 1962). 



In the research reported here, the validity of these methods of 

 differentiation was reassessed on the hypothesis that geographic variation 

 exists within the species of Cronartium. 



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